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Allow some dotdot lookups in capability mode.

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If dotdot lookup does not escape from the file descriptor passed as
the lookup root, we can allow the component traversal.  Track the
directories traversed, and check the result of dotdot lookup against
the recorded list of the directory vnodes.

Dotdot lookups are enabled by sysctl vfs.lookup_cap_dotdot, currently
disabled by default until more verification of the approach is done.

Disallow non-local filesystems for dotdot, since remote server might
conspire with the local process to allow it to escape the namespace.
This might be too cautious, provide the knob
vfs.lookup_cap_dotdot_nonlocal to override as well.

Idea by:	rwatson
Discussed with:	emaste, jonathan, rwatson
Reviewed by:	mjg (previous version)
Tested by:	pho (previous version)
Sponsored by:	The FreeBSD Foundation
MFC after:	2 week
Differential revision:	https://reviews.freebsd.org/D8110
This commit is contained in:
Konstantin Belousov 2016-11-02 12:43:15 +00:00
parent 1bf6a0900d
commit 7359fdcf5f
4 changed files with 145 additions and 16 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
sys/fs/nfsserver/nfs_nfsdport.c
View File

@ -350,7 +350,7 @@ nfsvno_namei(struct nfsrv_descript *nd, struct nameidata *ndp,
*retdirp = NULL;
cnp->cn_nameptr = cnp->cn_pnbuf;
ndp->ni_strictrelative = 0;
ndp->ni_lcf = 0;
/*
* Extract and set starting directory.
*/

143
sys/kern/vfs_lookup.c
View File

@ -79,12 +79,22 @@ uma_zone_t namei_zone;
/* Placeholder vnode for mp traversal. */
static struct vnode *vp_crossmp;
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, sizeof(void *), 0);
getnewvnode("crossmp", NULL, &dead_vnodeops, &vp_crossmp);
vn_lock(vp_crossmp, LK_EXCLUSIVE);
VN_LOCK_ASHARE(vp_crossmp);
@ -96,6 +106,76 @@ static int lookup_shared = 1;
SYSCTL_INT(_vfs, OID_AUTO, lookup_shared, CTLFLAG_RWTUN, &lookup_shared, 0,
"enables shared locks for path name translation");
/*
* Intent is that lookup_cap_dotdot becomes unconditionally enabled,
* but it defaults to the disabled state until verification efforts
* are complete.
*/
static int lookup_cap_dotdot = 0;
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 = 0;
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;
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)
{
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);
}
}
/*
* 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);
}
return (ENOTCAPABLE);
}
static void
namei_cleanup_cnp(struct componentname *cnp)
{
@ -113,7 +193,7 @@ namei_handle_root(struct nameidata *ndp, struct vnode **dpp)
struct componentname *cnp;
cnp = &ndp->ni_cnd;
if (ndp->ni_strictrelative != 0) {
if ((ndp->ni_lcf & NI_LCF_STRICTRELATIVE) != 0) {
#ifdef KTRACE
if (KTRPOINT(curthread, KTR_CAPFAIL))
ktrcapfail(CAPFAIL_LOOKUP, NULL, NULL);
@ -177,6 +257,8 @@ namei(struct nameidata *ndp)
if (!lookup_shared)
cnp->cn_flags &= ~LOCKSHARED;
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;
@ -202,13 +284,21 @@ namei(struct nameidata *ndp)
#ifdef CAPABILITY_MODE
/*
* In capability mode, lookups must be "strictly relative" (i.e.
* not an absolute path, and not containing '..' components) to
* a real file descriptor, not the pseudo-descriptor AT_FDCWD.
* 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_strictrelative = 1;
ndp->ni_lcf |= NI_LCF_STRICTRELATIVE;
if (ndp->ni_dirfd == AT_FDCWD) {
#ifdef KTRACE
if (KTRPOINT(td, KTR_CAPFAIL))
@ -282,7 +372,7 @@ namei(struct nameidata *ndp)
&rights) ||
ndp->ni_filecaps.fc_fcntls != CAP_FCNTL_ALL ||
ndp->ni_filecaps.fc_nioctls != -1) {
ndp->ni_strictrelative = 1;
ndp->ni_lcf |= NI_LCF_STRICTRELATIVE;
}
#endif
}
@ -297,6 +387,9 @@ namei(struct nameidata *ndp)
vrele(dp);
goto out;
}
if ((ndp->ni_lcf & NI_LCF_STRICTRELATIVE) != 0 &&
lookup_cap_dotdot != 0)
ndp->ni_lcf |= NI_LCF_CAP_DOTDOT;
SDT_PROBE3(vfs, namei, lookup, entry, dp, cnp->cn_pnbuf,
cnp->cn_flags);
for (;;) {
@ -313,7 +406,7 @@ namei(struct nameidata *ndp)
namei_cleanup_cnp(cnp);
} else
cnp->cn_flags |= HASBUF;
nameicap_cleanup(ndp);
SDT_PROBE2(vfs, namei, lookup, return, 0, ndp->ni_vp);
return (0);
}
@ -387,6 +480,7 @@ namei(struct nameidata *ndp)
out:
vrele(ndp->ni_rootdir);
namei_cleanup_cnp(cnp);
nameicap_cleanup(ndp);
SDT_PROBE2(vfs, namei, lookup, return, error, NULL);
return (error);
}
@ -583,6 +677,8 @@ lookup(struct nameidata *ndp)
goto bad;
}
nameicap_tracker_add(ndp, dp);
/*
* Check for degenerate name (e.g. / or "")
* which is a way of talking about a directory,
@ -618,9 +714,8 @@ lookup(struct nameidata *ndp)
/*
* Handle "..": five special cases.
* 0. If doing a capability lookup, return ENOTCAPABLE (this is a
* fairly conservative design choice, but it's the only one that we
* are satisfied guarantees the property we're looking for).
* 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)
@ -632,9 +727,15 @@ lookup(struct nameidata *ndp)
* .. 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_strictrelative != 0) {
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);
@ -676,6 +777,14 @@ lookup(struct nameidata *ndp)
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;
}
}
}
@ -735,6 +844,7 @@ lookup(struct nameidata *ndp)
vn_lock(dp,
compute_cn_lkflags(dp->v_mount, cnp->cn_lkflags |
LK_RETRY, cnp->cn_flags));
nameicap_tracker_add(ndp, dp);
goto unionlookup;
}
@ -855,6 +965,16 @@ lookup(struct nameidata *ndp)
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 == '/') {
@ -1081,7 +1201,6 @@ NDINIT_ALL(struct nameidata *ndp, u_long op, u_long flags, enum uio_seg segflg,
ndp->ni_dirp = namep;
ndp->ni_dirfd = dirfd;
ndp->ni_startdir = startdir;
ndp->ni_strictrelative = 0;
if (rightsp != NULL)
ndp->ni_rightsneeded = *rightsp;
else

4
sys/kern/vfs_syscalls.c
View File

@ -1030,7 +1030,7 @@ kern_openat(struct thread *td, int fd, char *path, enum uio_seg pathseg,
* understand exactly what would happen, and we don't think
* that it ever should.
*/
if (nd.ni_strictrelative == 0 &&
if ((nd.ni_lcf & NI_LCF_STRICTRELATIVE) == 0 &&
(error == ENODEV || error == ENXIO) &&
td->td_dupfd >= 0) {
error = dupfdopen(td, fdp, td->td_dupfd, flags, error,
@ -1076,7 +1076,7 @@ kern_openat(struct thread *td, int fd, char *path, enum uio_seg pathseg,
struct filecaps *fcaps;
#ifdef CAPABILITIES
if (nd.ni_strictrelative == 1)
if ((nd.ni_lcf & NI_LCF_STRICTRELATIVE) != 0)
fcaps = &nd.ni_filecaps;
else
#endif

12
sys/sys/namei.h
View File

@ -55,6 +55,9 @@ struct componentname {
long cn_namelen; /* length of looked up component */
};
struct nameicap_tracker;
TAILQ_HEAD(nameicap_tracker_head, nameicap_tracker);
/*
* Encapsulation of namei parameters.
*/
@ -72,7 +75,7 @@ struct nameidata {
struct vnode *ni_rootdir; /* logical root directory */
struct vnode *ni_topdir; /* logical top directory */
int ni_dirfd; /* starting directory for *at functions */
int ni_strictrelative; /* relative lookup only; no '..' */
int ni_lcf; /* local call flags */
/*
* Results: returned from namei
*/
@ -94,6 +97,7 @@ struct nameidata {
* through the VOP interface.
*/
struct componentname ni_cnd;
struct nameicap_tracker_head ni_cap_tracker;
};
#ifdef _KERNEL
@ -151,6 +155,12 @@ struct nameidata {
#define NOCAPCHECK 0x20000000 /* do not perform capability checks */
#define PARAMASK 0x3ffffe00 /* mask of parameter descriptors */
/*
* Flags in ni_lcf, valid for the duration of the namei call.
*/
#define NI_LCF_STRICTRELATIVE 0x0001 /* relative lookup only */
#define NI_LCF_CAP_DOTDOT 0x0002 /* ".." in strictrelative case */
/*
* Initialization of a nameidata structure.
*/