From 4bbbd5875d32f3cbe76235d90243f713eff9b9d0 Mon Sep 17 00:00:00 2001 From: Rick Macklem Date: Thu, 2 Mar 2023 13:09:01 -0800 Subject: [PATCH] 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 --- sys/kern/vfs_mount.c | 107 +++++++++++++++++++++++++++++++++++++------ 1 file changed, 93 insertions(+), 14 deletions(-) diff --git a/sys/kern/vfs_mount.c b/sys/kern/vfs_mount.c index a3990b9203dd..6233d4c3741a 100644 --- a/sys/kern/vfs_mount.c +++ b/sys/kern/vfs_mount.c @@ -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);