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freebsd-dev/sys/kern/vfs_lookup.c
Konstantin Belousov 7d2b0bd7d7 If BENEATH is specified, always latch the topping directory vnode. 
It is possible that we started with a relative path but during the
lookup, found an absolute symlink.  In this case, BENEATH handling
code needs the latch, but it is too late to calculate it.

While there, somewhat improve the assertions.  Clear the NI_LCF_LATCH
flag when the latch vnode is released, so that asserts know the state.
Assert that there is a latch if we entered beneath+abs path mode,
after the starting point is processed.

Reported by:	wulf
With more input from:	pho
Sponsored by:	The FreeBSD Foundation
2018-11-29 19:13:10 +00:00

1479 lines
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/*-
* SPDX-License-Identifier: BSD-3-Clause
*
* Copyright (c) 1982, 1986, 1989, 1993
* The Regents of the University of California. All rights reserved.
* (c) UNIX System Laboratories, Inc.
* All or some portions of this file are derived from material licensed
* to the University of California by American Telephone and Telegraph
* Co. or Unix System Laboratories, Inc. and are reproduced herein with
* the permission of UNIX System Laboratories, Inc.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. Neither the name of the University nor the names of its contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*
* @(#)vfs_lookup.c 8.4 (Berkeley) 2/16/94
*/
#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");
#include "opt_capsicum.h"
#include "opt_ktrace.h"
#include <sys/param.h>
#include <sys/systm.h>
#include <sys/kernel.h>
#include <sys/capsicum.h>
#include <sys/fcntl.h>
#include <sys/jail.h>
#include <sys/lock.h>
#include <sys/mutex.h>
#include <sys/namei.h>
#include <sys/vnode.h>
#include <sys/mount.h>
#include <sys/filedesc.h>
#include <sys/proc.h>
#include <sys/sdt.h>
#include <sys/syscallsubr.h>
#include <sys/sysctl.h>
#ifdef KTRACE
#include <sys/ktrace.h>
#endif
#include <security/audit/audit.h>
#include <security/mac/mac_framework.h>
#include <vm/uma.h>
#define NAMEI_DIAGNOSTIC 1
#undef NAMEI_DIAGNOSTIC
SDT_PROVIDER_DECLARE(vfs);
SDT_PROBE_DEFINE3(vfs, namei, lookup, entry, "struct vnode *", "char *",
"unsigned long");
SDT_PROBE_DEFINE2(vfs, namei, lookup, return, "int", "struct vnode *");
/* Allocation zone for namei. */
uma_zone_t namei_zone;
/* Placeholder vnode for mp traversal. */
static struct vnode *vp_crossmp;
static int
crossmp_vop_islocked(struct vop_islocked_args *ap)
{
return (LK_SHARED);
}
static int
crossmp_vop_lock1(struct vop_lock1_args *ap)
{
struct vnode *vp;
struct lock *lk __unused;
const char *file __unused;
int flags, line __unused;
vp = ap->a_vp;
lk = vp->v_vnlock;
flags = ap->a_flags;
file = ap->a_file;
line = ap->a_line;
if ((flags & LK_SHARED) == 0)
panic("invalid lock request for crossmp");
WITNESS_CHECKORDER(&lk->lock_object, LOP_NEWORDER, file, line,
flags & LK_INTERLOCK ? &VI_MTX(vp)->lock_object : NULL);
WITNESS_LOCK(&lk->lock_object, 0, file, line);
if ((flags & LK_INTERLOCK) != 0)
VI_UNLOCK(vp);
LOCK_LOG_LOCK("SLOCK", &lk->lock_object, 0, 0, ap->a_file, line);
return (0);
}
static int
crossmp_vop_unlock(struct vop_unlock_args *ap)
{
struct vnode *vp;
struct lock *lk __unused;
int flags;
vp = ap->a_vp;
lk = vp->v_vnlock;
flags = ap->a_flags;
if ((flags & LK_INTERLOCK) != 0)
VI_UNLOCK(vp);
WITNESS_UNLOCK(&lk->lock_object, 0, LOCK_FILE, LOCK_LINE);
LOCK_LOG_LOCK("SUNLOCK", &lk->lock_object, 0, 0, LOCK_FILE,
LOCK_LINE);
return (0);
}
static struct vop_vector crossmp_vnodeops = {
.vop_default = &default_vnodeops,
.vop_islocked = crossmp_vop_islocked,
.vop_lock1 = crossmp_vop_lock1,
.vop_unlock = crossmp_vop_unlock,
};
struct nameicap_tracker {
struct vnode *dp;
TAILQ_ENTRY(nameicap_tracker) nm_link;
};
/* Zone for cap mode tracker elements used for dotdot capability checks. */
static uma_zone_t nt_zone;
static void
nameiinit(void *dummy __unused)
{
namei_zone = uma_zcreate("NAMEI", MAXPATHLEN, NULL, NULL, NULL, NULL,
UMA_ALIGN_PTR, 0);
nt_zone = uma_zcreate("rentr", sizeof(struct nameicap_tracker),
NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0);
getnewvnode("crossmp", NULL, &crossmp_vnodeops, &vp_crossmp);
}
SYSINIT(vfs, SI_SUB_VFS, SI_ORDER_SECOND, nameiinit, NULL);
static int lookup_cap_dotdot = 1;
SYSCTL_INT(_vfs, OID_AUTO, lookup_cap_dotdot, CTLFLAG_RWTUN,
&lookup_cap_dotdot, 0,
"enables \"..\" components in path lookup in capability mode");
static int lookup_cap_dotdot_nonlocal = 1;
SYSCTL_INT(_vfs, OID_AUTO, lookup_cap_dotdot_nonlocal, CTLFLAG_RWTUN,
&lookup_cap_dotdot_nonlocal, 0,
"enables \"..\" components in path lookup in capability mode "
"on non-local mount");
static void
nameicap_tracker_add(struct nameidata *ndp, struct vnode *dp)
{
struct nameicap_tracker *nt;
if ((ndp->ni_lcf & NI_LCF_CAP_DOTDOT) == 0 || dp->v_type != VDIR)
return;
if ((ndp->ni_lcf & (NI_LCF_BENEATH_ABS | NI_LCF_BENEATH_LATCHED)) ==
NI_LCF_BENEATH_ABS) {
MPASS((ndp->ni_lcf & NI_LCF_LATCH) != 0);
if (dp != ndp->ni_beneath_latch)
return;
ndp->ni_lcf |= NI_LCF_BENEATH_LATCHED;
}
nt = uma_zalloc(nt_zone, M_WAITOK);
vhold(dp);
nt->dp = dp;
TAILQ_INSERT_TAIL(&ndp->ni_cap_tracker, nt, nm_link);
}
static void
nameicap_cleanup(struct nameidata *ndp, bool clean_latch)
{
struct nameicap_tracker *nt, *nt1;
KASSERT(TAILQ_EMPTY(&ndp->ni_cap_tracker) ||
(ndp->ni_lcf & NI_LCF_CAP_DOTDOT) != 0, ("not strictrelative"));
TAILQ_FOREACH_SAFE(nt, &ndp->ni_cap_tracker, nm_link, nt1) {
TAILQ_REMOVE(&ndp->ni_cap_tracker, nt, nm_link);
vdrop(nt->dp);
uma_zfree(nt_zone, nt);
}
if (clean_latch && (ndp->ni_lcf & NI_LCF_LATCH) != 0) {
ndp->ni_lcf &= ~NI_LCF_LATCH;
vrele(ndp->ni_beneath_latch);
}
}
/*
* For dotdot lookups in capability mode, only allow the component
* lookup to succeed if the resulting directory was already traversed
* during the operation. Also fail dotdot lookups for non-local
* filesystems, where external agents might assist local lookups to
* escape the compartment.
*/
static int
nameicap_check_dotdot(struct nameidata *ndp, struct vnode *dp)
{
struct nameicap_tracker *nt;
struct mount *mp;
if ((ndp->ni_lcf & NI_LCF_CAP_DOTDOT) == 0 || dp == NULL ||
dp->v_type != VDIR)
return (0);
mp = dp->v_mount;
if (lookup_cap_dotdot_nonlocal == 0 && mp != NULL &&
(mp->mnt_flag & MNT_LOCAL) == 0)
return (ENOTCAPABLE);
TAILQ_FOREACH_REVERSE(nt, &ndp->ni_cap_tracker, nameicap_tracker_head,
nm_link) {
if (dp == nt->dp)
return (0);
}
if ((ndp->ni_lcf & NI_LCF_BENEATH_ABS) != 0) {
ndp->ni_lcf &= ~NI_LCF_BENEATH_LATCHED;
nameicap_cleanup(ndp, false);
return (0);
}
return (ENOTCAPABLE);
}
static void
namei_cleanup_cnp(struct componentname *cnp)
{
uma_zfree(namei_zone, cnp->cn_pnbuf);
#ifdef DIAGNOSTIC
cnp->cn_pnbuf = NULL;
cnp->cn_nameptr = NULL;
#endif
}
static int
namei_handle_root(struct nameidata *ndp, struct vnode **dpp)
{
struct componentname *cnp;
cnp = &ndp->ni_cnd;
if ((ndp->ni_lcf & NI_LCF_STRICTRELATIVE) != 0) {
#ifdef KTRACE
if (KTRPOINT(curthread, KTR_CAPFAIL))
ktrcapfail(CAPFAIL_LOOKUP, NULL, NULL);
#endif
return (ENOTCAPABLE);
}
if ((cnp->cn_flags & BENEATH) != 0) {
ndp->ni_lcf |= NI_LCF_BENEATH_ABS;
ndp->ni_lcf &= ~NI_LCF_BENEATH_LATCHED;
nameicap_cleanup(ndp, false);
}
while (*(cnp->cn_nameptr) == '/') {
cnp->cn_nameptr++;
ndp->ni_pathlen--;
}
*dpp = ndp->ni_rootdir;
vrefact(*dpp);
return (0);
}
/*
* Convert a pathname into a pointer to a locked vnode.
*
* The FOLLOW flag is set when symbolic links are to be followed
* when they occur at the end of the name translation process.
* Symbolic links are always followed for all other pathname
* components other than the last.
*
* The segflg defines whether the name is to be copied from user
* space or kernel space.
*
* Overall outline of namei:
*
* copy in name
* get starting directory
* while (!done && !error) {
* call lookup to search path.
* if symbolic link, massage name in buffer and continue
* }
*/
int
namei(struct nameidata *ndp)
{
struct filedesc *fdp; /* pointer to file descriptor state */
char *cp; /* pointer into pathname argument */
struct vnode *dp; /* the directory we are searching */
struct iovec aiov; /* uio for reading symbolic links */
struct componentname *cnp;
struct thread *td;
struct proc *p;
cap_rights_t rights;
struct filecaps dirfd_caps;
struct uio auio;
int error, linklen, startdir_used;
cnp = &ndp->ni_cnd;
td = cnp->cn_thread;
p = td->td_proc;
ndp->ni_cnd.cn_cred = ndp->ni_cnd.cn_thread->td_ucred;
KASSERT(cnp->cn_cred && p, ("namei: bad cred/proc"));
KASSERT((cnp->cn_nameiop & (~OPMASK)) == 0,
("namei: nameiop contaminated with flags"));
KASSERT((cnp->cn_flags & OPMASK) == 0,
("namei: flags contaminated with nameiops"));
MPASS(ndp->ni_startdir == NULL || ndp->ni_startdir->v_type == VDIR ||
ndp->ni_startdir->v_type == VBAD);
fdp = p->p_fd;
TAILQ_INIT(&ndp->ni_cap_tracker);
ndp->ni_lcf = 0;
/* We will set this ourselves if we need it. */
cnp->cn_flags &= ~TRAILINGSLASH;
/*
* Get a buffer for the name to be translated, and copy the
* name into the buffer.
*/
if ((cnp->cn_flags & HASBUF) == 0)
cnp->cn_pnbuf = uma_zalloc(namei_zone, M_WAITOK);
if (ndp->ni_segflg == UIO_SYSSPACE)
error = copystr(ndp->ni_dirp, cnp->cn_pnbuf, MAXPATHLEN,
&ndp->ni_pathlen);
else
error = copyinstr(ndp->ni_dirp, cnp->cn_pnbuf, MAXPATHLEN,
&ndp->ni_pathlen);
/*
* Don't allow empty pathnames.
*/
if (error == 0 && *cnp->cn_pnbuf == '\0')
error = ENOENT;
#ifdef CAPABILITY_MODE
/*
* In capability mode, lookups must be restricted to happen in
* the subtree with the root specified by the file descriptor:
* - The root must be real file descriptor, not the pseudo-descriptor
* AT_FDCWD.
* - The passed path must be relative and not absolute.
* - If lookup_cap_dotdot is disabled, path must not contain the
* '..' components.
* - If lookup_cap_dotdot is enabled, we verify that all '..'
* components lookups result in the directories which were
* previously walked by us, which prevents an escape from
* the relative root.
*/
if (error == 0 && IN_CAPABILITY_MODE(td) &&
(cnp->cn_flags & NOCAPCHECK) == 0) {
ndp->ni_lcf |= NI_LCF_STRICTRELATIVE;
if (ndp->ni_dirfd == AT_FDCWD) {
#ifdef KTRACE
if (KTRPOINT(td, KTR_CAPFAIL))
ktrcapfail(CAPFAIL_LOOKUP, NULL, NULL);
#endif
error = ECAPMODE;
}
}
#endif
if (error != 0) {
namei_cleanup_cnp(cnp);
ndp->ni_vp = NULL;
return (error);
}
ndp->ni_loopcnt = 0;
#ifdef KTRACE
if (KTRPOINT(td, KTR_NAMEI)) {
KASSERT(cnp->cn_thread == curthread,
("namei not using curthread"));
ktrnamei(cnp->cn_pnbuf);
}
#endif
/*
* Get starting point for the translation.
*/
FILEDESC_SLOCK(fdp);
ndp->ni_rootdir = fdp->fd_rdir;
vrefact(ndp->ni_rootdir);
ndp->ni_topdir = fdp->fd_jdir;
/*
* If we are auditing the kernel pathname, save the user pathname.
*/
if (cnp->cn_flags & AUDITVNODE1)
AUDIT_ARG_UPATH1(td, ndp->ni_dirfd, cnp->cn_pnbuf);
if (cnp->cn_flags & AUDITVNODE2)
AUDIT_ARG_UPATH2(td, ndp->ni_dirfd, cnp->cn_pnbuf);
startdir_used = 0;
dp = NULL;
cnp->cn_nameptr = cnp->cn_pnbuf;
if (cnp->cn_pnbuf[0] == '/') {
error = namei_handle_root(ndp, &dp);
} else {
if (ndp->ni_startdir != NULL) {
dp = ndp->ni_startdir;
startdir_used = 1;
} else if (ndp->ni_dirfd == AT_FDCWD) {
dp = fdp->fd_cdir;
vrefact(dp);
} else {
rights = ndp->ni_rightsneeded;
cap_rights_set(&rights, CAP_LOOKUP);
if (cnp->cn_flags & AUDITVNODE1)
AUDIT_ARG_ATFD1(ndp->ni_dirfd);
if (cnp->cn_flags & AUDITVNODE2)
AUDIT_ARG_ATFD2(ndp->ni_dirfd);
error = fgetvp_rights(td, ndp->ni_dirfd,
&rights, &ndp->ni_filecaps, &dp);
if (error == EINVAL)
error = ENOTDIR;
#ifdef CAPABILITIES
/*
* If file descriptor doesn't have all rights,
* all lookups relative to it must also be
* strictly relative.
*/
CAP_ALL(&rights);
if (!cap_rights_contains(&ndp->ni_filecaps.fc_rights,
&rights) ||
ndp->ni_filecaps.fc_fcntls != CAP_FCNTL_ALL ||
ndp->ni_filecaps.fc_nioctls != -1) {
ndp->ni_lcf |= NI_LCF_STRICTRELATIVE;
}
#endif
}
if (error == 0 && dp->v_type != VDIR)
error = ENOTDIR;
}
if (error == 0 && (cnp->cn_flags & BENEATH) != 0) {
if (ndp->ni_dirfd == AT_FDCWD) {
ndp->ni_beneath_latch = fdp->fd_cdir;
vrefact(ndp->ni_beneath_latch);
} else {
rights = ndp->ni_rightsneeded;
cap_rights_set(&rights, CAP_LOOKUP);
error = fgetvp_rights(td, ndp->ni_dirfd, &rights,
&dirfd_caps, &ndp->ni_beneath_latch);
if (error == 0 && dp->v_type != VDIR) {
vrele(ndp->ni_beneath_latch);
error = ENOTDIR;
}
}
if (error == 0)
ndp->ni_lcf |= NI_LCF_LATCH;
}
FILEDESC_SUNLOCK(fdp);
if (ndp->ni_startdir != NULL && !startdir_used)
vrele(ndp->ni_startdir);
if (error != 0) {
if (dp != NULL)
vrele(dp);
goto out;
}
MPASS((ndp->ni_lcf & (NI_LCF_BENEATH_ABS | NI_LCF_LATCH)) !=
NI_LCF_BENEATH_ABS);
if (((ndp->ni_lcf & NI_LCF_STRICTRELATIVE) != 0 &&
lookup_cap_dotdot != 0) ||
((ndp->ni_lcf & NI_LCF_STRICTRELATIVE) == 0 &&
(cnp->cn_flags & BENEATH) != 0))
ndp->ni_lcf |= NI_LCF_CAP_DOTDOT;
SDT_PROBE3(vfs, namei, lookup, entry, dp, cnp->cn_pnbuf,
cnp->cn_flags);
for (;;) {
ndp->ni_startdir = dp;
error = lookup(ndp);
if (error != 0)
goto out;
/*
* If not a symbolic link, we're done.
*/
if ((cnp->cn_flags & ISSYMLINK) == 0) {
vrele(ndp->ni_rootdir);
if ((cnp->cn_flags & (SAVENAME | SAVESTART)) == 0) {
namei_cleanup_cnp(cnp);
} else
cnp->cn_flags |= HASBUF;
if ((ndp->ni_lcf & (NI_LCF_BENEATH_ABS |
NI_LCF_BENEATH_LATCHED)) == NI_LCF_BENEATH_ABS) {
NDFREE(ndp, 0);
error = ENOTCAPABLE;
}
nameicap_cleanup(ndp, true);
SDT_PROBE2(vfs, namei, lookup, return, error,
(error == 0 ? ndp->ni_vp : NULL));
return (error);
}
if (ndp->ni_loopcnt++ >= MAXSYMLINKS) {
error = ELOOP;
break;
}
#ifdef MAC
if ((cnp->cn_flags & NOMACCHECK) == 0) {
error = mac_vnode_check_readlink(td->td_ucred,
ndp->ni_vp);
if (error != 0)
break;
}
#endif
if (ndp->ni_pathlen > 1)
cp = uma_zalloc(namei_zone, M_WAITOK);
else
cp = cnp->cn_pnbuf;
aiov.iov_base = cp;
aiov.iov_len = MAXPATHLEN;
auio.uio_iov = &aiov;
auio.uio_iovcnt = 1;
auio.uio_offset = 0;
auio.uio_rw = UIO_READ;
auio.uio_segflg = UIO_SYSSPACE;
auio.uio_td = td;
auio.uio_resid = MAXPATHLEN;
error = VOP_READLINK(ndp->ni_vp, &auio, cnp->cn_cred);
if (error != 0) {
if (ndp->ni_pathlen > 1)
uma_zfree(namei_zone, cp);
break;
}
linklen = MAXPATHLEN - auio.uio_resid;
if (linklen == 0) {
if (ndp->ni_pathlen > 1)
uma_zfree(namei_zone, cp);
error = ENOENT;
break;
}
if (linklen + ndp->ni_pathlen > MAXPATHLEN) {
if (ndp->ni_pathlen > 1)
uma_zfree(namei_zone, cp);
error = ENAMETOOLONG;
break;
}
if (ndp->ni_pathlen > 1) {
bcopy(ndp->ni_next, cp + linklen, ndp->ni_pathlen);
uma_zfree(namei_zone, cnp->cn_pnbuf);
cnp->cn_pnbuf = cp;
} else
cnp->cn_pnbuf[linklen] = '\0';
ndp->ni_pathlen += linklen;
vput(ndp->ni_vp);
dp = ndp->ni_dvp;
/*
* Check if root directory should replace current directory.
*/
cnp->cn_nameptr = cnp->cn_pnbuf;
if (*(cnp->cn_nameptr) == '/') {
vrele(dp);
error = namei_handle_root(ndp, &dp);
if (error != 0)
goto out;
}
}
vput(ndp->ni_vp);
ndp->ni_vp = NULL;
vrele(ndp->ni_dvp);
out:
vrele(ndp->ni_rootdir);
MPASS(error != 0);
namei_cleanup_cnp(cnp);
nameicap_cleanup(ndp, true);
SDT_PROBE2(vfs, namei, lookup, return, error, NULL);
return (error);
}
static int
compute_cn_lkflags(struct mount *mp, int lkflags, int cnflags)
{
if (mp == NULL || ((lkflags & LK_SHARED) &&
(!(mp->mnt_kern_flag & MNTK_LOOKUP_SHARED) ||
((cnflags & ISDOTDOT) &&
(mp->mnt_kern_flag & MNTK_LOOKUP_EXCL_DOTDOT))))) {
lkflags &= ~LK_SHARED;
lkflags |= LK_EXCLUSIVE;
}
lkflags |= LK_NODDLKTREAT;
return (lkflags);
}
static __inline int
needs_exclusive_leaf(struct mount *mp, int flags)
{
/*
* Intermediate nodes can use shared locks, we only need to
* force an exclusive lock for leaf nodes.
*/
if ((flags & (ISLASTCN | LOCKLEAF)) != (ISLASTCN | LOCKLEAF))
return (0);
/* Always use exclusive locks if LOCKSHARED isn't set. */
if (!(flags & LOCKSHARED))
return (1);
/*
* For lookups during open(), if the mount point supports
* extended shared operations, then use a shared lock for the
* leaf node, otherwise use an exclusive lock.
*/
if ((flags & ISOPEN) != 0)
return (!MNT_EXTENDED_SHARED(mp));
/*
* Lookup requests outside of open() that specify LOCKSHARED
* only need a shared lock on the leaf vnode.
*/
return (0);
}
/*
* Search a pathname.
* This is a very central and rather complicated routine.
*
* The pathname is pointed to by ni_ptr and is of length ni_pathlen.
* The starting directory is taken from ni_startdir. The pathname is
* descended until done, or a symbolic link is encountered. The variable
* ni_more is clear if the path is completed; it is set to one if a
* symbolic link needing interpretation is encountered.
*
* The flag argument is LOOKUP, CREATE, RENAME, or DELETE depending on
* whether the name is to be looked up, created, renamed, or deleted.
* When CREATE, RENAME, or DELETE is specified, information usable in
* creating, renaming, or deleting a directory entry may be calculated.
* If flag has LOCKPARENT or'ed into it, the parent directory is returned
* locked. If flag has WANTPARENT or'ed into it, the parent directory is
* returned unlocked. Otherwise the parent directory is not returned. If
* the target of the pathname exists and LOCKLEAF is or'ed into the flag
* the target is returned locked, otherwise it is returned unlocked.
* When creating or renaming and LOCKPARENT is specified, the target may not
* be ".". When deleting and LOCKPARENT is specified, the target may be ".".
*
* Overall outline of lookup:
*
* dirloop:
* identify next component of name at ndp->ni_ptr
* handle degenerate case where name is null string
* if .. and crossing mount points and on mounted filesys, find parent
* call VOP_LOOKUP routine for next component name
* directory vnode returned in ni_dvp, unlocked unless LOCKPARENT set
* component vnode returned in ni_vp (if it exists), locked.
* if result vnode is mounted on and crossing mount points,
* find mounted on vnode
* if more components of name, do next level at dirloop
* return the answer in ni_vp, locked if LOCKLEAF set
* if LOCKPARENT set, return locked parent in ni_dvp
* if WANTPARENT set, return unlocked parent in ni_dvp
*/
int
lookup(struct nameidata *ndp)
{
char *cp; /* pointer into pathname argument */
char *prev_ni_next; /* saved ndp->ni_next */
struct vnode *dp = NULL; /* the directory we are searching */
struct vnode *tdp; /* saved dp */
struct mount *mp; /* mount table entry */
struct prison *pr;
size_t prev_ni_pathlen; /* saved ndp->ni_pathlen */
int docache; /* == 0 do not cache last component */
int wantparent; /* 1 => wantparent or lockparent flag */
int rdonly; /* lookup read-only flag bit */
int error = 0;
int dpunlocked = 0; /* dp has already been unlocked */
int relookup = 0; /* do not consume the path component */
struct componentname *cnp = &ndp->ni_cnd;
int lkflags_save;
int ni_dvp_unlocked;
/*
* Setup: break out flag bits into variables.
*/
ni_dvp_unlocked = 0;
wantparent = cnp->cn_flags & (LOCKPARENT | WANTPARENT);
KASSERT(cnp->cn_nameiop == LOOKUP || wantparent,
("CREATE, DELETE, RENAME require LOCKPARENT or WANTPARENT."));
docache = (cnp->cn_flags & NOCACHE) ^ NOCACHE;
if (cnp->cn_nameiop == DELETE ||
(wantparent && cnp->cn_nameiop != CREATE &&
cnp->cn_nameiop != LOOKUP))
docache = 0;
rdonly = cnp->cn_flags & RDONLY;
cnp->cn_flags &= ~ISSYMLINK;
ndp->ni_dvp = NULL;
/*
* We use shared locks until we hit the parent of the last cn then
* we adjust based on the requesting flags.
*/
cnp->cn_lkflags = LK_SHARED;
dp = ndp->ni_startdir;
ndp->ni_startdir = NULLVP;
vn_lock(dp,
compute_cn_lkflags(dp->v_mount, cnp->cn_lkflags | LK_RETRY,
cnp->cn_flags));
dirloop:
/*
* Search a new directory.
*
* The last component of the filename is left accessible via
* cnp->cn_nameptr for callers that need the name. Callers needing
* the name set the SAVENAME flag. When done, they assume
* responsibility for freeing the pathname buffer.
*/
for (cp = cnp->cn_nameptr; *cp != 0 && *cp != '/'; cp++)
continue;
cnp->cn_namelen = cp - cnp->cn_nameptr;
if (cnp->cn_namelen > NAME_MAX) {
error = ENAMETOOLONG;
goto bad;
}
#ifdef NAMEI_DIAGNOSTIC
{ char c = *cp;
*cp = '\0';
printf("{%s}: ", cnp->cn_nameptr);
*cp = c; }
#endif
prev_ni_pathlen = ndp->ni_pathlen;
ndp->ni_pathlen -= cnp->cn_namelen;
KASSERT(ndp->ni_pathlen <= PATH_MAX,
("%s: ni_pathlen underflow to %zd\n", __func__, ndp->ni_pathlen));
prev_ni_next = ndp->ni_next;
ndp->ni_next = cp;
/*
* Replace multiple slashes by a single slash and trailing slashes
* by a null. This must be done before VOP_LOOKUP() because some
* fs's don't know about trailing slashes. Remember if there were
* trailing slashes to handle symlinks, existing non-directories
* and non-existing files that won't be directories specially later.
*/
while (*cp == '/' && (cp[1] == '/' || cp[1] == '\0')) {
cp++;
ndp->ni_pathlen--;
if (*cp == '\0') {
*ndp->ni_next = '\0';
cnp->cn_flags |= TRAILINGSLASH;
}
}
ndp->ni_next = cp;
cnp->cn_flags |= MAKEENTRY;
if (*cp == '\0' && docache == 0)
cnp->cn_flags &= ~MAKEENTRY;
if (cnp->cn_namelen == 2 &&
cnp->cn_nameptr[1] == '.' && cnp->cn_nameptr[0] == '.')
cnp->cn_flags |= ISDOTDOT;
else
cnp->cn_flags &= ~ISDOTDOT;
if (*ndp->ni_next == 0)
cnp->cn_flags |= ISLASTCN;
else
cnp->cn_flags &= ~ISLASTCN;
if ((cnp->cn_flags & ISLASTCN) != 0 &&
cnp->cn_namelen == 1 && cnp->cn_nameptr[0] == '.' &&
(cnp->cn_nameiop == DELETE || cnp->cn_nameiop == RENAME)) {
error = EINVAL;
goto bad;
}
nameicap_tracker_add(ndp, dp);
/*
* Check for degenerate name (e.g. / or "")
* which is a way of talking about a directory,
* e.g. like "/." or ".".
*/
if (cnp->cn_nameptr[0] == '\0') {
if (dp->v_type != VDIR) {
error = ENOTDIR;
goto bad;
}
if (cnp->cn_nameiop != LOOKUP) {
error = EISDIR;
goto bad;
}
if (wantparent) {
ndp->ni_dvp = dp;
VREF(dp);
}
ndp->ni_vp = dp;
if (cnp->cn_flags & AUDITVNODE1)
AUDIT_ARG_VNODE1(dp);
else if (cnp->cn_flags & AUDITVNODE2)
AUDIT_ARG_VNODE2(dp);
if (!(cnp->cn_flags & (LOCKPARENT | LOCKLEAF)))
VOP_UNLOCK(dp, 0);
/* XXX This should probably move to the top of function. */
if (cnp->cn_flags & SAVESTART)
panic("lookup: SAVESTART");
goto success;
}
/*
* Handle "..": five special cases.
* 0. If doing a capability lookup and lookup_cap_dotdot is
* disabled, return ENOTCAPABLE.
* 1. Return an error if this is the last component of
* the name and the operation is DELETE or RENAME.
* 2. If at root directory (e.g. after chroot)
* or at absolute root directory
* then ignore it so can't get out.
* 3. If this vnode is the root of a mounted
* filesystem, then replace it with the
* vnode which was mounted on so we take the
* .. in the other filesystem.
* 4. If the vnode is the top directory of
* the jail or chroot, don't let them out.
* 5. If doing a capability lookup and lookup_cap_dotdot is
* enabled, return ENOTCAPABLE if the lookup would escape
* from the initial file descriptor directory. Checks are
* done by ensuring that namei() already traversed the
* result of dotdot lookup.
*/
if (cnp->cn_flags & ISDOTDOT) {
if ((ndp->ni_lcf & (NI_LCF_STRICTRELATIVE | NI_LCF_CAP_DOTDOT))
== NI_LCF_STRICTRELATIVE) {
#ifdef KTRACE
if (KTRPOINT(curthread, KTR_CAPFAIL))
ktrcapfail(CAPFAIL_LOOKUP, NULL, NULL);
#endif
error = ENOTCAPABLE;
goto bad;
}
if ((cnp->cn_flags & ISLASTCN) != 0 &&
(cnp->cn_nameiop == DELETE || cnp->cn_nameiop == RENAME)) {
error = EINVAL;
goto bad;
}
for (;;) {
for (pr = cnp->cn_cred->cr_prison; pr != NULL;
pr = pr->pr_parent)
if (dp == pr->pr_root)
break;
if (dp == ndp->ni_rootdir ||
dp == ndp->ni_topdir ||
dp == rootvnode ||
pr != NULL ||
((dp->v_vflag & VV_ROOT) != 0 &&
(cnp->cn_flags & NOCROSSMOUNT) != 0)) {
ndp->ni_dvp = dp;
ndp->ni_vp = dp;
VREF(dp);
goto nextname;
}
if ((dp->v_vflag & VV_ROOT) == 0)
break;
if (dp->v_iflag & VI_DOOMED) { /* forced unmount */
error = ENOENT;
goto bad;
}
tdp = dp;
dp = dp->v_mount->mnt_vnodecovered;
VREF(dp);
vput(tdp);
vn_lock(dp,
compute_cn_lkflags(dp->v_mount, cnp->cn_lkflags |
LK_RETRY, ISDOTDOT));
error = nameicap_check_dotdot(ndp, dp);
if (error != 0) {
#ifdef KTRACE
if (KTRPOINT(curthread, KTR_CAPFAIL))
ktrcapfail(CAPFAIL_LOOKUP, NULL, NULL);
#endif
goto bad;
}
}
}
/*
* We now have a segment name to search for, and a directory to search.
*/
unionlookup:
#ifdef MAC
if ((cnp->cn_flags & NOMACCHECK) == 0) {
error = mac_vnode_check_lookup(cnp->cn_thread->td_ucred, dp,
cnp);
if (error)
goto bad;
}
#endif
ndp->ni_dvp = dp;
ndp->ni_vp = NULL;
ASSERT_VOP_LOCKED(dp, "lookup");
/*
* If we have a shared lock we may need to upgrade the lock for the
* last operation.
*/
if ((cnp->cn_flags & LOCKPARENT) && (cnp->cn_flags & ISLASTCN) &&
dp != vp_crossmp && VOP_ISLOCKED(dp) == LK_SHARED)
vn_lock(dp, LK_UPGRADE|LK_RETRY);
if ((dp->v_iflag & VI_DOOMED) != 0) {
error = ENOENT;
goto bad;
}
/*
* If we're looking up the last component and we need an exclusive
* lock, adjust our lkflags.
*/
if (needs_exclusive_leaf(dp->v_mount, cnp->cn_flags))
cnp->cn_lkflags = LK_EXCLUSIVE;
#ifdef NAMEI_DIAGNOSTIC
vn_printf(dp, "lookup in ");
#endif
lkflags_save = cnp->cn_lkflags;
cnp->cn_lkflags = compute_cn_lkflags(dp->v_mount, cnp->cn_lkflags,
cnp->cn_flags);
error = VOP_LOOKUP(dp, &ndp->ni_vp, cnp);
cnp->cn_lkflags = lkflags_save;
if (error != 0) {
KASSERT(ndp->ni_vp == NULL, ("leaf should be empty"));
#ifdef NAMEI_DIAGNOSTIC
printf("not found\n");
#endif
if ((error == ENOENT) &&
(dp->v_vflag & VV_ROOT) && (dp->v_mount != NULL) &&
(dp->v_mount->mnt_flag & MNT_UNION)) {
tdp = dp;
dp = dp->v_mount->mnt_vnodecovered;
VREF(dp);
vput(tdp);
vn_lock(dp,
compute_cn_lkflags(dp->v_mount, cnp->cn_lkflags |
LK_RETRY, cnp->cn_flags));
nameicap_tracker_add(ndp, dp);
goto unionlookup;
}
if (error == ERELOOKUP) {
vref(dp);
ndp->ni_vp = dp;
error = 0;
relookup = 1;
goto good;
}
if (error != EJUSTRETURN)
goto bad;
/*
* At this point, we know we're at the end of the
* pathname. If creating / renaming, we can consider
* allowing the file or directory to be created / renamed,
* provided we're not on a read-only filesystem.
*/
if (rdonly) {
error = EROFS;
goto bad;
}
/* trailing slash only allowed for directories */
if ((cnp->cn_flags & TRAILINGSLASH) &&
!(cnp->cn_flags & WILLBEDIR)) {
error = ENOENT;
goto bad;
}
if ((cnp->cn_flags & LOCKPARENT) == 0)
VOP_UNLOCK(dp, 0);
/*
* We return with ni_vp NULL to indicate that the entry
* doesn't currently exist, leaving a pointer to the
* (possibly locked) directory vnode in ndp->ni_dvp.
*/
if (cnp->cn_flags & SAVESTART) {
ndp->ni_startdir = ndp->ni_dvp;
VREF(ndp->ni_startdir);
}
goto success;
}
good:
#ifdef NAMEI_DIAGNOSTIC
printf("found\n");
#endif
dp = ndp->ni_vp;
/*
* Check to see if the vnode has been mounted on;
* if so find the root of the mounted filesystem.
*/
while (dp->v_type == VDIR && (mp = dp->v_mountedhere) &&
(cnp->cn_flags & NOCROSSMOUNT) == 0) {
if (vfs_busy(mp, 0))
continue;
vput(dp);
if (dp != ndp->ni_dvp)
vput(ndp->ni_dvp);
else
vrele(ndp->ni_dvp);
vrefact(vp_crossmp);
ndp->ni_dvp = vp_crossmp;
error = VFS_ROOT(mp, compute_cn_lkflags(mp, cnp->cn_lkflags,
cnp->cn_flags), &tdp);
vfs_unbusy(mp);
if (vn_lock(vp_crossmp, LK_SHARED | LK_NOWAIT))
panic("vp_crossmp exclusively locked or reclaimed");
if (error) {
dpunlocked = 1;
goto bad2;
}
ndp->ni_vp = dp = tdp;
}
/*
* Check for symbolic link
*/
if ((dp->v_type == VLNK) &&
((cnp->cn_flags & FOLLOW) || (cnp->cn_flags & TRAILINGSLASH) ||
*ndp->ni_next == '/')) {
cnp->cn_flags |= ISSYMLINK;
if (dp->v_iflag & VI_DOOMED) {
/*
* We can't know whether the directory was mounted with
* NOSYMFOLLOW, so we can't follow safely.
*/
error = ENOENT;
goto bad2;
}
if (dp->v_mount->mnt_flag & MNT_NOSYMFOLLOW) {
error = EACCES;
goto bad2;
}
/*
* Symlink code always expects an unlocked dvp.
*/
if (ndp->ni_dvp != ndp->ni_vp) {
VOP_UNLOCK(ndp->ni_dvp, 0);
ni_dvp_unlocked = 1;
}
goto success;
}
nextname:
/*
* Not a symbolic link that we will follow. Continue with the
* next component if there is any; otherwise, we're done.
*/
KASSERT((cnp->cn_flags & ISLASTCN) || *ndp->ni_next == '/',
("lookup: invalid path state."));
if (relookup) {
relookup = 0;
ndp->ni_pathlen = prev_ni_pathlen;
ndp->ni_next = prev_ni_next;
if (ndp->ni_dvp != dp)
vput(ndp->ni_dvp);
else
vrele(ndp->ni_dvp);
goto dirloop;
}
if (cnp->cn_flags & ISDOTDOT) {
error = nameicap_check_dotdot(ndp, ndp->ni_vp);
if (error != 0) {
#ifdef KTRACE
if (KTRPOINT(curthread, KTR_CAPFAIL))
ktrcapfail(CAPFAIL_LOOKUP, NULL, NULL);
#endif
goto bad2;
}
}
if (*ndp->ni_next == '/') {
cnp->cn_nameptr = ndp->ni_next;
while (*cnp->cn_nameptr == '/') {
cnp->cn_nameptr++;
ndp->ni_pathlen--;
}
if (ndp->ni_dvp != dp)
vput(ndp->ni_dvp);
else
vrele(ndp->ni_dvp);
goto dirloop;
}
/*
* If we're processing a path with a trailing slash,
* check that the end result is a directory.
*/
if ((cnp->cn_flags & TRAILINGSLASH) && dp->v_type != VDIR) {
error = ENOTDIR;
goto bad2;
}
/*
* Disallow directory write attempts on read-only filesystems.
*/
if (rdonly &&
(cnp->cn_nameiop == DELETE || cnp->cn_nameiop == RENAME)) {
error = EROFS;
goto bad2;
}
if (cnp->cn_flags & SAVESTART) {
ndp->ni_startdir = ndp->ni_dvp;
VREF(ndp->ni_startdir);
}
if (!wantparent) {
ni_dvp_unlocked = 2;
if (ndp->ni_dvp != dp)
vput(ndp->ni_dvp);
else
vrele(ndp->ni_dvp);
} else if ((cnp->cn_flags & LOCKPARENT) == 0 && ndp->ni_dvp != dp) {
VOP_UNLOCK(ndp->ni_dvp, 0);
ni_dvp_unlocked = 1;
}
if (cnp->cn_flags & AUDITVNODE1)
AUDIT_ARG_VNODE1(dp);
else if (cnp->cn_flags & AUDITVNODE2)
AUDIT_ARG_VNODE2(dp);
if ((cnp->cn_flags & LOCKLEAF) == 0)
VOP_UNLOCK(dp, 0);
success:
/*
* Because of shared lookup we may have the vnode shared locked, but
* the caller may want it to be exclusively locked.
*/
if (needs_exclusive_leaf(dp->v_mount, cnp->cn_flags) &&
VOP_ISLOCKED(dp) != LK_EXCLUSIVE) {
vn_lock(dp, LK_UPGRADE | LK_RETRY);
if (dp->v_iflag & VI_DOOMED) {
error = ENOENT;
goto bad2;
}
}
return (0);
bad2:
if (ni_dvp_unlocked != 2) {
if (dp != ndp->ni_dvp && !ni_dvp_unlocked)
vput(ndp->ni_dvp);
else
vrele(ndp->ni_dvp);
}
bad:
if (!dpunlocked)
vput(dp);
ndp->ni_vp = NULL;
return (error);
}
/*
* relookup - lookup a path name component
* Used by lookup to re-acquire things.
*/
int
relookup(struct vnode *dvp, struct vnode **vpp, struct componentname *cnp)
{
struct vnode *dp = NULL; /* the directory we are searching */
int wantparent; /* 1 => wantparent or lockparent flag */
int rdonly; /* lookup read-only flag bit */
int error = 0;
KASSERT(cnp->cn_flags & ISLASTCN,
("relookup: Not given last component."));
/*
* Setup: break out flag bits into variables.
*/
wantparent = cnp->cn_flags & (LOCKPARENT|WANTPARENT);
KASSERT(wantparent, ("relookup: parent not wanted."));
rdonly = cnp->cn_flags & RDONLY;
cnp->cn_flags &= ~ISSYMLINK;
dp = dvp;
cnp->cn_lkflags = LK_EXCLUSIVE;
vn_lock(dp, LK_EXCLUSIVE | LK_RETRY);
/*
* Search a new directory.
*
* The last component of the filename is left accessible via
* cnp->cn_nameptr for callers that need the name. Callers needing
* the name set the SAVENAME flag. When done, they assume
* responsibility for freeing the pathname buffer.
*/
#ifdef NAMEI_DIAGNOSTIC
printf("{%s}: ", cnp->cn_nameptr);
#endif
/*
* Check for "" which represents the root directory after slash
* removal.
*/
if (cnp->cn_nameptr[0] == '\0') {
/*
* Support only LOOKUP for "/" because lookup()
* can't succeed for CREATE, DELETE and RENAME.
*/
KASSERT(cnp->cn_nameiop == LOOKUP, ("nameiop must be LOOKUP"));
KASSERT(dp->v_type == VDIR, ("dp is not a directory"));
if (!(cnp->cn_flags & LOCKLEAF))
VOP_UNLOCK(dp, 0);
*vpp = dp;
/* XXX This should probably move to the top of function. */
if (cnp->cn_flags & SAVESTART)
panic("lookup: SAVESTART");
return (0);
}
if (cnp->cn_flags & ISDOTDOT)
panic ("relookup: lookup on dot-dot");
/*
* We now have a segment name to search for, and a directory to search.
*/
#ifdef NAMEI_DIAGNOSTIC
vn_printf(dp, "search in ");
#endif
if ((error = VOP_LOOKUP(dp, vpp, cnp)) != 0) {
KASSERT(*vpp == NULL, ("leaf should be empty"));
if (error != EJUSTRETURN)
goto bad;
/*
* If creating and at end of pathname, then can consider
* allowing file to be created.
*/
if (rdonly) {
error = EROFS;
goto bad;
}
/* ASSERT(dvp == ndp->ni_startdir) */
if (cnp->cn_flags & SAVESTART)
VREF(dvp);
if ((cnp->cn_flags & LOCKPARENT) == 0)
VOP_UNLOCK(dp, 0);
/*
* We return with ni_vp NULL to indicate that the entry
* doesn't currently exist, leaving a pointer to the
* (possibly locked) directory vnode in ndp->ni_dvp.
*/
return (0);
}
dp = *vpp;
/*
* Disallow directory write attempts on read-only filesystems.
*/
if (rdonly &&
(cnp->cn_nameiop == DELETE || cnp->cn_nameiop == RENAME)) {
if (dvp == dp)
vrele(dvp);
else
vput(dvp);
error = EROFS;
goto bad;
}
/*
* Set the parent lock/ref state to the requested state.
*/
if ((cnp->cn_flags & LOCKPARENT) == 0 && dvp != dp) {
if (wantparent)
VOP_UNLOCK(dvp, 0);
else
vput(dvp);
} else if (!wantparent)
vrele(dvp);
/*
* Check for symbolic link
*/
KASSERT(dp->v_type != VLNK || !(cnp->cn_flags & FOLLOW),
("relookup: symlink found.\n"));
/* ASSERT(dvp == ndp->ni_startdir) */
if (cnp->cn_flags & SAVESTART)
VREF(dvp);
if ((cnp->cn_flags & LOCKLEAF) == 0)
VOP_UNLOCK(dp, 0);
return (0);
bad:
vput(dp);
*vpp = NULL;
return (error);
}
void
NDINIT_ALL(struct nameidata *ndp, u_long op, u_long flags, enum uio_seg segflg,
const char *namep, int dirfd, struct vnode *startdir, cap_rights_t *rightsp,
struct thread *td)
{
ndp->ni_cnd.cn_nameiop = op;
ndp->ni_cnd.cn_flags = flags;
ndp->ni_segflg = segflg;
ndp->ni_dirp = namep;
ndp->ni_dirfd = dirfd;
ndp->ni_startdir = startdir;
if (rightsp != NULL)
ndp->ni_rightsneeded = *rightsp;
else
cap_rights_init(&ndp->ni_rightsneeded);
filecaps_init(&ndp->ni_filecaps);
ndp->ni_cnd.cn_thread = td;
}
/*
* Free data allocated by namei(); see namei(9) for details.
*/
void
NDFREE(struct nameidata *ndp, const u_int flags)
{
int unlock_dvp;
int unlock_vp;
unlock_dvp = 0;
unlock_vp = 0;
if (!(flags & NDF_NO_FREE_PNBUF) &&
(ndp->ni_cnd.cn_flags & HASBUF)) {
uma_zfree(namei_zone, ndp->ni_cnd.cn_pnbuf);
ndp->ni_cnd.cn_flags &= ~HASBUF;
}
if (!(flags & NDF_NO_VP_UNLOCK) &&
(ndp->ni_cnd.cn_flags & LOCKLEAF) && ndp->ni_vp)
unlock_vp = 1;
if (!(flags & NDF_NO_VP_RELE) && ndp->ni_vp) {
if (unlock_vp) {
vput(ndp->ni_vp);
unlock_vp = 0;
} else
vrele(ndp->ni_vp);
ndp->ni_vp = NULL;
}
if (unlock_vp)
VOP_UNLOCK(ndp->ni_vp, 0);
if (!(flags & NDF_NO_DVP_UNLOCK) &&
(ndp->ni_cnd.cn_flags & LOCKPARENT) &&
ndp->ni_dvp != ndp->ni_vp)
unlock_dvp = 1;
if (!(flags & NDF_NO_DVP_RELE) &&
(ndp->ni_cnd.cn_flags & (LOCKPARENT|WANTPARENT))) {
if (unlock_dvp) {
vput(ndp->ni_dvp);
unlock_dvp = 0;
} else
vrele(ndp->ni_dvp);
ndp->ni_dvp = NULL;
}
if (unlock_dvp)
VOP_UNLOCK(ndp->ni_dvp, 0);
if (!(flags & NDF_NO_STARTDIR_RELE) &&
(ndp->ni_cnd.cn_flags & SAVESTART)) {
vrele(ndp->ni_startdir);
ndp->ni_startdir = NULL;
}
}
/*
* Determine if there is a suitable alternate filename under the specified
* prefix for the specified path. If the create flag is set, then the
* alternate prefix will be used so long as the parent directory exists.
* This is used by the various compatibility ABIs so that Linux binaries prefer
* files under /compat/linux for example. The chosen path (whether under
* the prefix or under /) is returned in a kernel malloc'd buffer pointed
* to by pathbuf. The caller is responsible for free'ing the buffer from
* the M_TEMP bucket if one is returned.
*/
int
kern_alternate_path(struct thread *td, const char *prefix, const char *path,
enum uio_seg pathseg, char **pathbuf, int create, int dirfd)
{
struct nameidata nd, ndroot;
char *ptr, *buf, *cp;
size_t len, sz;
int error;
buf = (char *) malloc(MAXPATHLEN, M_TEMP, M_WAITOK);
*pathbuf = buf;
/* Copy the prefix into the new pathname as a starting point. */
len = strlcpy(buf, prefix, MAXPATHLEN);
if (len >= MAXPATHLEN) {
*pathbuf = NULL;
free(buf, M_TEMP);
return (EINVAL);
}
sz = MAXPATHLEN - len;
ptr = buf + len;
/* Append the filename to the prefix. */
if (pathseg == UIO_SYSSPACE)
error = copystr(path, ptr, sz, &len);
else
error = copyinstr(path, ptr, sz, &len);
if (error) {
*pathbuf = NULL;
free(buf, M_TEMP);
return (error);
}
/* Only use a prefix with absolute pathnames. */
if (*ptr != '/') {
error = EINVAL;
goto keeporig;
}
if (dirfd != AT_FDCWD) {
/*
* We want the original because the "prefix" is
* included in the already opened dirfd.
*/
bcopy(ptr, buf, len);
return (0);
}
/*
* We know that there is a / somewhere in this pathname.
* Search backwards for it, to find the file's parent dir
* to see if it exists in the alternate tree. If it does,
* and we want to create a file (cflag is set). We don't
* need to worry about the root comparison in this case.
*/
if (create) {
for (cp = &ptr[len] - 1; *cp != '/'; cp--);
*cp = '\0';
NDINIT(&nd, LOOKUP, NOFOLLOW, UIO_SYSSPACE, buf, td);
error = namei(&nd);
*cp = '/';
if (error != 0)
goto keeporig;
} else {
NDINIT(&nd, LOOKUP, NOFOLLOW, UIO_SYSSPACE, buf, td);
error = namei(&nd);
if (error != 0)
goto keeporig;
/*
* We now compare the vnode of the prefix to the one
* vnode asked. If they resolve to be the same, then we
* ignore the match so that the real root gets used.
* This avoids the problem of traversing "../.." to find the
* root directory and never finding it, because "/" resolves
* to the emulation root directory. This is expensive :-(
*/
NDINIT(&ndroot, LOOKUP, FOLLOW, UIO_SYSSPACE, prefix,
td);
/* We shouldn't ever get an error from this namei(). */
error = namei(&ndroot);
if (error == 0) {
if (nd.ni_vp == ndroot.ni_vp)
error = ENOENT;
NDFREE(&ndroot, NDF_ONLY_PNBUF);
vrele(ndroot.ni_vp);
}
}
NDFREE(&nd, NDF_ONLY_PNBUF);
vrele(nd.ni_vp);
keeporig:
/* If there was an error, use the original path name. */
if (error)
bcopy(ptr, buf, len);
return (error);
}
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