vfs_mount.c: Allow mountd(8) to do exports in a vnet prison
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
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@ -78,7 +78,8 @@ __FBSDID("$FreeBSD$");
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#define VFS_MOUNTARG_SIZE_MAX (1024 * 64)
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static int vfs_domount(struct thread *td, const char *fstype, char *fspath,
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uint64_t fsflags, struct vfsoptlist **optlist);
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uint64_t fsflags, bool jail_export,
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struct vfsoptlist **optlist);
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static void free_mntarg(struct mntarg *ma);
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static int usermount = 0;
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@ -806,7 +807,7 @@ vfs_donmount(struct thread *td, uint64_t fsflags, struct uio *fsoptions)
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struct vfsopt *opt, *tmp_opt;
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char *fstype, *fspath, *errmsg;
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int error, fstypelen, fspathlen, errmsg_len, errmsg_pos;
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bool autoro;
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bool autoro, has_nonexport, jail_export;
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errmsg = fspath = NULL;
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errmsg_len = fspathlen = 0;
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@ -842,15 +843,37 @@ vfs_donmount(struct thread *td, uint64_t fsflags, struct uio *fsoptions)
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goto bail;
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}
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/*
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* Check to see that "export" is only used with the "update", "fstype",
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* "fspath", "from" and "errmsg" options when in a vnet jail.
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* These are the ones used to set/update exports by mountd(8).
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* If only the above options are set in a jail that can run mountd(8),
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* then the jail_export argument of vfs_domount() will be true.
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* When jail_export is true, the vfs_suser() check does not cause
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* failure, but limits the update to exports only.
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* This allows mountd(8) running within the vnet jail
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* to export file systems visible within the jail, but
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* mounted outside of the jail.
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*/
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/*
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* We need to see if we have the "update" option
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* before we call vfs_domount(), since vfs_domount() has special
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* logic based on MNT_UPDATE. This is very important
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* when we want to update the root filesystem.
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*/
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has_nonexport = false;
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jail_export = false;
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TAILQ_FOREACH_SAFE(opt, optlist, link, tmp_opt) {
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int do_freeopt = 0;
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if (jailed(td->td_ucred) &&
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strcmp(opt->name, "export") != 0 &&
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strcmp(opt->name, "update") != 0 &&
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strcmp(opt->name, "fstype") != 0 &&
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strcmp(opt->name, "fspath") != 0 &&
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strcmp(opt->name, "from") != 0 &&
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strcmp(opt->name, "errmsg") != 0)
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has_nonexport = true;
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if (strcmp(opt->name, "update") == 0) {
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fsflags |= MNT_UPDATE;
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do_freeopt = 1;
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@ -933,9 +956,10 @@ vfs_donmount(struct thread *td, uint64_t fsflags, struct uio *fsoptions)
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fsflags |= MNT_SYNCHRONOUS;
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else if (strcmp(opt->name, "union") == 0)
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fsflags |= MNT_UNION;
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else if (strcmp(opt->name, "export") == 0)
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else if (strcmp(opt->name, "export") == 0) {
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fsflags |= MNT_EXPORTED;
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else if (strcmp(opt->name, "automounted") == 0) {
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jail_export = true;
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} else if (strcmp(opt->name, "automounted") == 0) {
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fsflags |= MNT_AUTOMOUNTED;
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do_freeopt = 1;
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} else if (strcmp(opt->name, "nocover") == 0) {
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@ -965,7 +989,15 @@ vfs_donmount(struct thread *td, uint64_t fsflags, struct uio *fsoptions)
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goto bail;
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}
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error = vfs_domount(td, fstype, fspath, fsflags, &optlist);
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/*
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* If has_nonexport is true or the caller is not running within a
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* vnet prison that can run mountd(8), set jail_export false.
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*/
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if (has_nonexport || !jailed(td->td_ucred) ||
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!prison_check_nfsd(td->td_ucred))
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jail_export = false;
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error = vfs_domount(td, fstype, fspath, fsflags, jail_export, &optlist);
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if (error == ENOENT) {
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error = EINVAL;
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if (errmsg != NULL)
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@ -983,7 +1015,8 @@ vfs_donmount(struct thread *td, uint64_t fsflags, struct uio *fsoptions)
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printf("%s: R/W mount failed, possibly R/O media,"
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" trying R/O mount\n", __func__);
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fsflags |= MNT_RDONLY;
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error = vfs_domount(td, fstype, fspath, fsflags, &optlist);
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error = vfs_domount(td, fstype, fspath, fsflags, jail_export,
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&optlist);
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}
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bail:
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/* copyout the errmsg */
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@ -1273,6 +1306,7 @@ vfs_domount_update(
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struct thread *td, /* Calling thread. */
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struct vnode *vp, /* Mount point vnode. */
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uint64_t fsflags, /* Flags common to all filesystems. */
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bool jail_export, /* Got export option in vnet prison. */
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struct vfsoptlist **optlist /* Options local to the filesystem. */
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)
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{
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@ -1284,6 +1318,7 @@ vfs_domount_update(
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int error, export_error, i, len;
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uint64_t flag;
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gid_t *grps;
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bool vfs_suser_failed;
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ASSERT_VOP_ELOCKED(vp, __func__);
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KASSERT((fsflags & MNT_UPDATE) != 0, ("MNT_UPDATE should be here"));
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@ -1312,7 +1347,20 @@ vfs_domount_update(
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* Only privileged root, or (if MNT_USER is set) the user that
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* did the original mount is permitted to update it.
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*/
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/*
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* For the case of mountd(8) doing exports in a jail, the vfs_suser()
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* call does not cause failure. vfs_domount() has already checked
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* that "root" is doing this and vfs_suser() will fail when
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* the file system has been mounted outside the jail.
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* jail_export set true indicates that "export" is not mixed
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* with other options that change mount behaviour.
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*/
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vfs_suser_failed = false;
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error = vfs_suser(mp, td);
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if (jail_export && error != 0) {
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error = 0;
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vfs_suser_failed = true;
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}
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if (error != 0) {
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vput(vp);
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return (error);
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@ -1342,11 +1390,26 @@ vfs_domount_update(
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error = EBUSY;
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goto end;
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}
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if (vfs_suser_failed) {
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KASSERT((fsflags & (MNT_EXPORTED | MNT_UPDATE)) ==
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(MNT_EXPORTED | MNT_UPDATE),
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("%s: jailed export did not set expected fsflags",
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__func__));
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/*
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* For this case, only MNT_UPDATE and
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* MNT_EXPORTED have been set in fsflags
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* by the options. Only set MNT_UPDATE,
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* since that is the one that would be set
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* when set in fsflags, below.
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*/
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mp->mnt_flag |= MNT_UPDATE;
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} else {
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mp->mnt_flag &= ~MNT_UPDATEMASK;
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mp->mnt_flag |= fsflags & (MNT_RELOAD | MNT_FORCE | MNT_UPDATE |
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MNT_SNAPSHOT | MNT_ROOTFS | MNT_UPDATEMASK | MNT_RDONLY);
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if ((mp->mnt_flag & MNT_ASYNC) == 0)
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mp->mnt_kern_flag &= ~MNTK_ASYNC;
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}
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rootvp = vfs_cache_root_clear(mp);
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MNT_IUNLOCK(mp);
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mp->mnt_optnew = *optlist;
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@ -1357,6 +1420,16 @@ vfs_domount_update(
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* XXX The final recipients of VFS_MOUNT just overwrite the ndp they
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* get. No freeing of cn_pnbuf.
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*/
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/*
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* For the case of mountd(8) doing exports from within a vnet jail,
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* "from" is typically not set correctly such that VFS_MOUNT() will
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* return ENOENT. It is not obvious that VFS_MOUNT() ever needs to be
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* called when mountd is doing exports, but this check only applies to
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* the specific case where it is running inside a vnet jail, to
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* avoid any POLA violation.
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*/
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error = 0;
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if (!jail_export)
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error = VFS_MOUNT(mp);
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export_error = 0;
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@ -1495,6 +1568,7 @@ vfs_domount(
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const char *fstype, /* Filesystem type. */
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char *fspath, /* Mount path. */
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uint64_t fsflags, /* Flags common to all filesystems. */
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bool jail_export, /* Got export option in vnet prison. */
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struct vfsoptlist **optlist /* Options local to the filesystem. */
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)
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{
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@ -1512,7 +1586,11 @@ vfs_domount(
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if (strlen(fstype) >= MFSNAMELEN || strlen(fspath) >= MNAMELEN)
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return (ENAMETOOLONG);
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if (jailed(td->td_ucred) || usermount == 0) {
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if (jail_export) {
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error = priv_check(td, PRIV_NFS_DAEMON);
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if (error)
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return (error);
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} else if (jailed(td->td_ucred) || usermount == 0) {
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if ((error = priv_check(td, PRIV_VFS_MOUNT)) != 0)
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return (error);
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}
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@ -1593,7 +1671,8 @@ vfs_domount(
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}
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free(pathbuf, M_TEMP);
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} else
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error = vfs_domount_update(td, vp, fsflags, optlist);
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error = vfs_domount_update(td, vp, fsflags, jail_export,
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optlist);
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out:
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NDFREE_PNBUF(&nd);
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