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vfs_mount.c: Allow mountd(8) to do exports in a vnet prison

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To run mountd in a vnet prison, three checks in vfs_domount()
and vfs_domount_update() related to doing exports needed
to be changed, so that a file system visible within the
prison but mounted outside the prison can be exported.

I did all three in a minimal way, only changing the checks for
the specific case of a process (typically mountd) doing exports
within a vnet prison and not updating the mount point in other
ways.  The changes are:
- Ignore the error return from vfs_suser(), since the file
  system being mounted outside the prison will cause it to fail.
- Use the priv_check(PRIV_NFS_DAEMON) for this specific case
  within a prison.
- Skip the call to VFS_MOUNT(), since it will return an error,
  due to the "from" argument not being set correctly.  VFS_MOUNT()
  does not appear to do anything for the case of doing exports only.

Reviewed by:	markj
MFC after:	3 months
Differential Revision:	https://reviews.freebsd.org/D37741
This commit is contained in:
Rick Macklem 2023-03-02 13:09:01 -08:00
parent c7a8502bdf
commit 4bbbd5875d
1 changed files with 93 additions and 14 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

107
sys/kern/vfs_mount.c
View File

@ -78,7 +78,8 @@ __FBSDID("$FreeBSD$");
#define VFS_MOUNTARG_SIZE_MAX (1024 * 64)
static int vfs_domount(struct thread *td, const char *fstype, char *fspath,
uint64_t fsflags, struct vfsoptlist **optlist);
uint64_t fsflags, bool jail_export,
struct vfsoptlist **optlist);
static void free_mntarg(struct mntarg *ma);
static int usermount = 0;
@ -806,7 +807,7 @@ vfs_donmount(struct thread *td, uint64_t fsflags, struct uio *fsoptions)
struct vfsopt *opt, *tmp_opt;
char *fstype, *fspath, *errmsg;
int error, fstypelen, fspathlen, errmsg_len, errmsg_pos;
bool autoro;
bool autoro, has_nonexport, jail_export;
errmsg = fspath = NULL;
errmsg_len = fspathlen = 0;
@ -842,15 +843,37 @@ vfs_donmount(struct thread *td, uint64_t fsflags, struct uio *fsoptions)
goto bail;
}
/*
* Check to see that "export" is only used with the "update", "fstype",
* "fspath", "from" and "errmsg" options when in a vnet jail.
* These are the ones used to set/update exports by mountd(8).
* If only the above options are set in a jail that can run mountd(8),
* then the jail_export argument of vfs_domount() will be true.
* When jail_export is true, the vfs_suser() check does not cause
* failure, but limits the update to exports only.
* This allows mountd(8) running within the vnet jail
* to export file systems visible within the jail, but
* mounted outside of the jail.
*/
/*
* We need to see if we have the "update" option
* before we call vfs_domount(), since vfs_domount() has special
* logic based on MNT_UPDATE. This is very important
* when we want to update the root filesystem.
*/
has_nonexport = false;
jail_export = false;
TAILQ_FOREACH_SAFE(opt, optlist, link, tmp_opt) {
int do_freeopt = 0;
if (jailed(td->td_ucred) &&
strcmp(opt->name, "export") != 0 &&
strcmp(opt->name, "update") != 0 &&
strcmp(opt->name, "fstype") != 0 &&
strcmp(opt->name, "fspath") != 0 &&
strcmp(opt->name, "from") != 0 &&
strcmp(opt->name, "errmsg") != 0)
has_nonexport = true;
if (strcmp(opt->name, "update") == 0) {
fsflags |= MNT_UPDATE;
do_freeopt = 1;
@ -933,9 +956,10 @@ vfs_donmount(struct thread *td, uint64_t fsflags, struct uio *fsoptions)
fsflags |= MNT_SYNCHRONOUS;
else if (strcmp(opt->name, "union") == 0)
fsflags |= MNT_UNION;
else if (strcmp(opt->name, "export") == 0)
else if (strcmp(opt->name, "export") == 0) {
fsflags |= MNT_EXPORTED;
else if (strcmp(opt->name, "automounted") == 0) {
jail_export = true;
} else if (strcmp(opt->name, "automounted") == 0) {
fsflags |= MNT_AUTOMOUNTED;
do_freeopt = 1;
} else if (strcmp(opt->name, "nocover") == 0) {
@ -965,7 +989,15 @@ vfs_donmount(struct thread *td, uint64_t fsflags, struct uio *fsoptions)
goto bail;
}
error = vfs_domount(td, fstype, fspath, fsflags, &optlist);
/*
* If has_nonexport is true or the caller is not running within a
* vnet prison that can run mountd(8), set jail_export false.
*/
if (has_nonexport || !jailed(td->td_ucred) ||
!prison_check_nfsd(td->td_ucred))
jail_export = false;
error = vfs_domount(td, fstype, fspath, fsflags, jail_export, &optlist);
if (error == ENOENT) {
error = EINVAL;
if (errmsg != NULL)
@ -983,7 +1015,8 @@ vfs_donmount(struct thread *td, uint64_t fsflags, struct uio *fsoptions)
printf("%s: R/W mount failed, possibly R/O media,"
" trying R/O mount\n", __func__);
fsflags |= MNT_RDONLY;
error = vfs_domount(td, fstype, fspath, fsflags, &optlist);
error = vfs_domount(td, fstype, fspath, fsflags, jail_export,
&optlist);
}
bail:
/* copyout the errmsg */
@ -1273,6 +1306,7 @@ vfs_domount_update(
struct thread *td, /* Calling thread. */
struct vnode *vp, /* Mount point vnode. */
uint64_t fsflags, /* Flags common to all filesystems. */
bool jail_export, /* Got export option in vnet prison. */
struct vfsoptlist **optlist /* Options local to the filesystem. */
)
{
@ -1284,6 +1318,7 @@ vfs_domount_update(
int error, export_error, i, len;
uint64_t flag;
gid_t *grps;
bool vfs_suser_failed;
ASSERT_VOP_ELOCKED(vp, __func__);
KASSERT((fsflags & MNT_UPDATE) != 0, ("MNT_UPDATE should be here"));
@ -1312,7 +1347,20 @@ vfs_domount_update(
* Only privileged root, or (if MNT_USER is set) the user that
* did the original mount is permitted to update it.
*/
/*
* For the case of mountd(8) doing exports in a jail, the vfs_suser()
* call does not cause failure. vfs_domount() has already checked
* that "root" is doing this and vfs_suser() will fail when
* the file system has been mounted outside the jail.
* jail_export set true indicates that "export" is not mixed
* with other options that change mount behaviour.
*/
vfs_suser_failed = false;
error = vfs_suser(mp, td);
if (jail_export && error != 0) {
error = 0;
vfs_suser_failed = true;
}
if (error != 0) {
vput(vp);
return (error);
@ -1342,11 +1390,26 @@ vfs_domount_update(
error = EBUSY;
goto end;
}
mp->mnt_flag &= ~MNT_UPDATEMASK;
mp->mnt_flag |= fsflags & (MNT_RELOAD | MNT_FORCE | MNT_UPDATE |
MNT_SNAPSHOT | MNT_ROOTFS | MNT_UPDATEMASK | MNT_RDONLY);
if ((mp->mnt_flag & MNT_ASYNC) == 0)
mp->mnt_kern_flag &= ~MNTK_ASYNC;
if (vfs_suser_failed) {
KASSERT((fsflags & (MNT_EXPORTED | MNT_UPDATE)) ==
(MNT_EXPORTED | MNT_UPDATE),
("%s: jailed export did not set expected fsflags",
__func__));
/*
* For this case, only MNT_UPDATE and
* MNT_EXPORTED have been set in fsflags
* by the options. Only set MNT_UPDATE,
* since that is the one that would be set
* when set in fsflags, below.
*/
mp->mnt_flag |= MNT_UPDATE;
} else {
mp->mnt_flag &= ~MNT_UPDATEMASK;
mp->mnt_flag |= fsflags & (MNT_RELOAD | MNT_FORCE | MNT_UPDATE |
MNT_SNAPSHOT | MNT_ROOTFS | MNT_UPDATEMASK | MNT_RDONLY);
if ((mp->mnt_flag & MNT_ASYNC) == 0)
mp->mnt_kern_flag &= ~MNTK_ASYNC;
}
rootvp = vfs_cache_root_clear(mp);
MNT_IUNLOCK(mp);
mp->mnt_optnew = *optlist;
@ -1357,7 +1420,17 @@ vfs_domount_update(
* XXX The final recipients of VFS_MOUNT just overwrite the ndp they
* get. No freeing of cn_pnbuf.
*/
error = VFS_MOUNT(mp);
/*
* For the case of mountd(8) doing exports from within a vnet jail,
* "from" is typically not set correctly such that VFS_MOUNT() will
* return ENOENT. It is not obvious that VFS_MOUNT() ever needs to be
* called when mountd is doing exports, but this check only applies to
* the specific case where it is running inside a vnet jail, to
* avoid any POLA violation.
*/
error = 0;
if (!jail_export)
error = VFS_MOUNT(mp);
export_error = 0;
/* Process the export option. */
@ -1495,6 +1568,7 @@ vfs_domount(
const char *fstype, /* Filesystem type. */
char *fspath, /* Mount path. */
uint64_t fsflags, /* Flags common to all filesystems. */
bool jail_export, /* Got export option in vnet prison. */
struct vfsoptlist **optlist /* Options local to the filesystem. */
)
{
@ -1512,7 +1586,11 @@ vfs_domount(
if (strlen(fstype) >= MFSNAMELEN || strlen(fspath) >= MNAMELEN)
return (ENAMETOOLONG);
if (jailed(td->td_ucred) || usermount == 0) {
if (jail_export) {
error = priv_check(td, PRIV_NFS_DAEMON);
if (error)
return (error);
} else if (jailed(td->td_ucred) || usermount == 0) {
if ((error = priv_check(td, PRIV_VFS_MOUNT)) != 0)
return (error);
}
@ -1593,7 +1671,8 @@ vfs_domount(
}
free(pathbuf, M_TEMP);
} else
error = vfs_domount_update(td, vp, fsflags, optlist);
error = vfs_domount_update(td, vp, fsflags, jail_export,
optlist);
out:
NDFREE_PNBUF(&nd);