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Jeff Layton 094f7b69ea selinux: make security_sb_clone_mnt_opts return an error on context mismatch 
I had the following problem reported a while back. If you mount the
same filesystem twice using NFSv4 with different contexts, then the
second context= option is ignored. For instance:

    # mount server:/export /mnt/test1
    # mount server:/export /mnt/test2 -o context=system_u:object_r:tmp_t:s0
    # ls -dZ /mnt/test1
    drwxrwxrwt. root root system_u:object_r:nfs_t:s0       /mnt/test1
    # ls -dZ /mnt/test2
    drwxrwxrwt. root root system_u:object_r:nfs_t:s0       /mnt/test2

When we call into SELinux to set the context of a "cloned" superblock,
it will currently just bail out when it notices that we're reusing an
existing superblock. Since the existing superblock is already set up and
presumably in use, we can't go overwriting its context with the one from
the "original" sb. Because of this, the second context= option in this
case cannot take effect.

This patch fixes this by turning security_sb_clone_mnt_opts into an int
return operation. When it finds that the "new" superblock that it has
been handed is already set up, it checks to see whether the contexts on
the old superblock match it. If it does, then it will just return
success, otherwise it'll return -EBUSY and emit a printk to tell the
admin why the second mount failed.

Note that this patch may cause casualties. The NFSv4 code relies on
being able to walk down to an export from the pseudoroot. If you mount
filesystems that are nested within one another with different contexts,
then this patch will make those mounts fail in new and "exciting" ways.

For instance, suppose that /export is a separate filesystem on the
server:

    # mount server:/ /mnt/test1
    # mount salusa:/export /mnt/test2 -o context=system_u:object_r:tmp_t:s0
    mount.nfs: an incorrect mount option was specified

...with the printk in the ring buffer. Because we *might* eventually
walk down to /mnt/test1/export, the mount is denied due to this patch.
The second mount needs the pseudoroot superblock, but that's already
present with the wrong context.

OTOH, if we mount these in the reverse order, then both mounts work,
because the pseudoroot superblock created when mounting /export is
discarded once that mount is done. If we then however try to walk into
that directory, the automount fails for the similar reasons:

    # cd /mnt/test1/scratch/
    -bash: cd: /mnt/test1/scratch: Device or resource busy

The story I've gotten from the SELinux folks that I've talked to is that
this is desirable behavior. In SELinux-land, mounting the same data
under different contexts is wrong -- there can be only one.

Cc: Steve Dickson <steved@redhat.com>
Cc: Stephen Smalley <sds@tycho.nsa.gov>
Signed-off-by: Jeff Layton <jlayton@redhat.com>
Acked-by: Eric Paris <eparis@redhat.com>
Signed-off-by: James Morris <james.l.morris@oracle.com>
 		2013-04-02 11:30:13 +11:00
..
9p fs: Limit sys_mount to only request filesystem modules. 2013-03-03 19:36:31 -08:00
adfs fs: Limit sys_mount to only request filesystem modules. 2013-03-03 19:36:31 -08:00
affs fs: Limit sys_mount to only request filesystem modules. 2013-03-03 19:36:31 -08:00
afs fs: Limit sys_mount to only request filesystem modules. 2013-03-03 19:36:31 -08:00
autofs4 fs: Limit sys_mount to only request filesystem modules. 2013-03-03 19:36:31 -08:00
befs fs: Limit sys_mount to only request filesystem modules. 2013-03-03 19:36:31 -08:00
bfs fs: Limit sys_mount to only request filesystem modules. 2013-03-03 19:36:31 -08:00
btrfs Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace 2013-03-09 16:51:13 -08:00
cachefiles FS-Cache: Mark cancellation of in-progress operation 2012-12-20 22:34:00 +00:00
ceph fs: Limit sys_mount to only request filesystem modules. 2013-03-03 19:36:31 -08:00
cifs CIFS: Fix missing of oplock_read value in smb30_values structure 2013-03-06 19:37:01 -06:00
coda fs: Limit sys_mount to only request filesystem modules. 2013-03-03 19:36:31 -08:00
configfs fs: Limit sys_mount to only request filesystem modules. 2013-03-03 19:36:31 -08:00
cramfs fs: Limit sys_mount to only request filesystem modules. 2013-03-03 19:36:31 -08:00
debugfs fs: Limit sys_mount to only request filesystem modules. 2013-03-03 19:36:31 -08:00
devpts fs: Limit sys_mount to only request filesystem modules (Part 2). 2013-03-07 01:08:55 -08:00
dlm hlist: drop the node parameter from iterators 2013-02-27 19:10:24 -08:00
ecryptfs Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace 2013-03-09 16:51:13 -08:00
efs fs: Limit sys_mount to only request filesystem modules. 2013-03-03 19:36:31 -08:00
exofs fs: Limit sys_mount to only request filesystem modules. 2013-03-03 19:36:31 -08:00
exportfs hlist: drop the node parameter from iterators 2013-02-27 19:10:24 -08:00
ext2 fs: Limit sys_mount to only request filesystem modules. 2013-03-03 19:36:31 -08:00
ext3 fs: Limit sys_mount to only request filesystem modules. 2013-03-03 19:36:31 -08:00
ext4 fs: Limit sys_mount to only request filesystem modules. 2013-03-03 19:36:31 -08:00
f2fs fs: Limit sys_mount to only request filesystem modules. 2013-03-03 19:36:31 -08:00
fat fs: Limit sys_mount to only request filesystem modules. 2013-03-03 19:36:31 -08:00
freevxfs fs: Limit sys_mount to only request filesystem modules. 2013-03-03 19:36:31 -08:00
fscache hlist: drop the node parameter from iterators 2013-02-27 19:10:24 -08:00
fuse fs: Limit sys_mount to only request filesystem modules. 2013-03-03 19:36:31 -08:00
gfs2 fs: Limit sys_mount to only request filesystem modules. 2013-03-03 19:36:31 -08:00
hfs fs: Limit sys_mount to only request filesystem modules. 2013-03-03 19:36:31 -08:00
hfsplus fs: Limit sys_mount to only request filesystem modules. 2013-03-03 19:36:31 -08:00
hostfs hostfs: directory methods have no business in non-directory inode_operations 2013-02-22 23:31:37 -05:00
hpfs Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2013-02-26 20:16:07 -08:00
hppfs fs: Limit sys_mount to only request filesystem modules. 2013-03-03 19:36:31 -08:00
hugetlbfs fs: Limit sys_mount to only request filesystem modules. 2013-03-03 19:36:31 -08:00
isofs fs: Limit sys_mount to only request filesystem modules. 2013-03-03 19:36:31 -08:00
jbd jbd: don't wake kjournald unnecessarily 2013-01-14 22:50:45 +01:00
jbd2 jbd2: fix ERR_PTR dereference in jbd2__journal_start 2013-03-02 17:08:46 -05:00
jffs2 fs: Limit sys_mount to only request filesystem modules. 2013-03-03 19:36:31 -08:00
jfs fs: Limit sys_mount to only request filesystem modules. 2013-03-03 19:36:31 -08:00
lockd Merge branch 'for-3.9' of git://linux-nfs.org/~bfields/linux 2013-02-28 18:02:55 -08:00
logfs fs: Limit sys_mount to only request filesystem modules. 2013-03-03 19:36:31 -08:00
minix fs: Limit sys_mount to only request filesystem modules. 2013-03-03 19:36:31 -08:00
ncpfs fs: Limit sys_mount to only request filesystem modules. 2013-03-03 19:36:31 -08:00
nfs selinux: make security_sb_clone_mnt_opts return an error on context mismatch 2013-04-02 11:30:13 +11:00
nfs_common nfs_common: Update the translation between nfsv3 acls linux posix acls 2013-02-13 06:15:14 -08:00
nfsd fs: Limit sys_mount to only request filesystem modules. 2013-03-03 19:36:31 -08:00
nilfs2 fs: Limit sys_mount to only request filesystem modules. 2013-03-03 19:36:31 -08:00
nls
…
notify hlist: drop the node parameter from iterators 2013-02-27 19:10:24 -08:00
ntfs fs: Limit sys_mount to only request filesystem modules. 2013-03-03 19:36:31 -08:00
ocfs2 fs: Limit sys_mount to only request filesystem modules (Part 2). 2013-03-07 01:08:55 -08:00
omfs fs: Limit sys_mount to only request filesystem modules. 2013-03-03 19:36:31 -08:00
openpromfs fs: Limit sys_mount to only request filesystem modules. 2013-03-03 19:36:31 -08:00
proc proc: Use nd_jump_link in proc_ns_follow_link 2013-03-09 00:14:45 -08:00
pstore A few fixes to reduce places where pstore might hang 2013-02-21 09:38:18 -08:00
qnx4 fs: Limit sys_mount to only request filesystem modules. 2013-03-03 19:36:31 -08:00
qnx6 fs: Limit sys_mount to only request filesystem modules. 2013-03-03 19:36:31 -08:00
quota quota: Use the pre-processor to compile out quotactl_cmd_write when !CONFIG_BLOCK 2012-12-13 16:33:24 +01:00
ramfs Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2013-02-26 20:16:07 -08:00
reiserfs fs: Limit sys_mount to only request filesystem modules. 2013-03-03 19:36:31 -08:00
romfs fs: Limit sys_mount to only request filesystem modules. 2013-03-03 19:36:31 -08:00
squashfs new helper: file_inode(file) 2013-02-22 23:31:31 -05:00
sysfs hlist: drop the node parameter from iterators 2013-02-27 19:10:24 -08:00
sysv fs: Limit sys_mount to only request filesystem modules. 2013-03-03 19:36:31 -08:00
ubifs fs: Limit sys_mount to only request filesystem modules. 2013-03-03 19:36:31 -08:00
udf Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2013-02-26 20:16:07 -08:00
ufs fs: Limit sys_mount to only request filesystem modules. 2013-03-03 19:36:31 -08:00
xfs fs: Limit sys_mount to only request filesystem modules. 2013-03-03 19:36:31 -08:00
Kconfig fuse: Move CUSE Kconfig entry from fs/Kconfig into fs/fuse/Kconfig 2013-01-17 13:08:45 +01:00
Kconfig.binfmt coredump: make core dump functionality optional 2012-10-06 03:05:15 +09:00
Makefile f2fs: update Kconfig and Makefile 2012-12-11 13:43:42 +09:00
aio.c hlist: drop the node parameter from iterators 2013-02-27 19:10:24 -08:00
anon_inodes.c get_empty_filp()/alloc_file() leave both ->f_pos and ->f_version zero 2013-02-26 02:46:11 -05:00
attr.c userns: Allow chown and setgid preservation 2012-11-20 04:17:24 -08:00
bad_inode.c lseek: the "whence" argument is called "whence" 2012-12-17 17:15:12 -08:00
binfmt_aout.c new helper: file_inode(file) 2013-02-22 23:31:31 -05:00
binfmt_elf.c ImgTec Meta architecture changes for v3.9-rc1 2013-03-03 12:06:09 -08:00
binfmt_elf_fdpic.c Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2013-02-26 20:16:07 -08:00
binfmt_em86.c exec: use -ELOOP for max recursion depth 2012-12-17 17:15:23 -08:00
binfmt_flat.c new helper: file_inode(file) 2013-02-22 23:31:31 -05:00
binfmt_misc.c fs: Limit sys_mount to only request filesystem modules. 2013-03-03 19:36:31 -08:00
binfmt_script.c exec: do not leave bprm->interp on stack 2012-12-20 17:40:19 -08:00
binfmt_som.c get rid of pt_regs argument of ->load_binary() 2012-11-28 21:53:38 -05:00
bio-integrity.c block: Ues bi_pool for bio_integrity_alloc() 2012-09-09 10:35:38 +02:00
bio.c block: add missing block_bio_complete() tracepoint 2013-01-14 15:00:36 +01:00
block_dev.c Merge branch 'for-3.9/core' of git://git.kernel.dk/linux-block 2013-02-28 12:52:24 -08:00
buffer.c Merge branch 'for-3.9/core' of git://git.kernel.dk/linux-block 2013-02-28 12:52:24 -08:00
char_dev.c char_dev: pin parent kobject 2012-10-22 08:50:37 +03:00
compat.c switch timerfd compat syscalls to COMPAT_SYSCALL_DEFINE 2013-02-03 15:09:25 -05:00
compat_binfmt_elf.c coredump: extend core dump note section to contain file names of mapped files 2012-10-06 03:05:17 +09:00
compat_ioctl.c new helper: file_inode(file) 2013-02-22 23:31:31 -05:00
coredump.c coredump: remove redundant defines for dumpable states 2013-02-27 19:10:11 -08:00
coredump.h coredump: update coredump-related headers 2012-10-06 03:05:15 +09:00
dcache.c hlist: drop the node parameter from iterators 2013-02-27 19:10:24 -08:00
dcookies.c
…
direct-io.c fs: Fix possible use-after-free with AIO 2013-02-22 23:31:36 -05:00
drop_caches.c
…
eventfd.c fs, eventfd: add procfs fdinfo helper 2012-12-17 17:15:27 -08:00
eventpoll.c epoll: prevent missed events on EPOLL_CTL_MOD 2013-01-02 09:16:43 -08:00
exec.c coredump: remove redundant defines for dumpable states 2013-02-27 19:10:11 -08:00
fcntl.c new helper: file_inode(file) 2013-02-22 23:31:31 -05:00
fhandle.c Merge branch 'for-3.8' of git://linux-nfs.org/~bfields/linux 2012-12-20 14:04:11 -08:00
fifo.c
…
file.c locking: Various static lock initializer fixes 2013-02-19 08:42:45 +01:00
file_table.c cache the value of file_inode() in struct file 2013-03-01 19:48:30 -05:00
filesystems.c fs: Limit sys_mount to only request filesystem modules. 2013-03-03 19:36:31 -08:00
fs-writeback.c 2 writeback fixes 2013-02-28 13:21:44 -08:00
fs_struct.c constify path_get/path_put and fs_struct.c stuff 2013-03-01 23:51:07 -05:00
generic_acl.c userns: Pass a userns parameter into posix_acl_to_xattr and posix_acl_from_xattr 2012-09-18 01:01:35 -07:00
inode.c hlist: drop the node parameter from iterators 2013-02-27 19:10:24 -08:00
internal.h constify path_get/path_put and fs_struct.c stuff 2013-03-01 23:51:07 -05:00
ioctl.c new helper: file_inode(file) 2013-02-22 23:31:31 -05:00
ioprio.c
…
libfs.c vfs: drop vmtruncate 2012-12-20 18:46:29 -05:00
locks.c new helper: file_inode(file) 2013-02-22 23:31:31 -05:00
mbcache.c
…
mount.h proc: Usable inode numbers for the namespace file descriptors. 2012-11-20 04:19:49 -08:00
mpage.c
…
namei.c vfs: don't BUG_ON() if following a /proc fd pseudo-symlink results in a symlink 2013-03-08 09:03:07 -08:00
namespace.c new helper: file_inode(file) 2013-02-22 23:31:31 -05:00
no-block.c
…
open.c Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2013-03-03 13:23:03 -08:00
pipe.c fs: Preserve error code in get_empty_filp(), part 2 2013-02-22 23:31:32 -05:00
pnode.c
…
pnode.h vfs: Only support slave subtrees across different user namespaces 2012-11-19 05:59:20 -08:00
posix_acl.c userns: Convert vfs posix_acl support to use kuids and kgids 2012-09-18 01:01:35 -07:00
proc_namespace.c
…
read_write.c Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/signal 2013-03-02 08:34:06 -08:00
read_write.h compat: fs: Generic compat_sys_sendfile implementation 2012-10-02 21:35:55 -04:00
readdir.c new helper: file_inode(file) 2013-02-22 23:31:31 -05:00
select.c sched/rt: Move rt specific bits into new header file 2013-02-07 20:51:08 +01:00
seq_file.c Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2013-03-03 13:23:03 -08:00
signalfd.c fs, epoll: add procfs fdinfo helper 2012-12-17 17:15:27 -08:00
splice.c export kernel_write(), convert open-coded instances 2013-02-26 02:46:11 -05:00
stack.c
…
stat.c switch vfs_getattr() to struct path 2013-02-26 02:46:08 -05:00
statfs.c vfs: fix user_statfs to retry once on ESTALE errors 2012-12-20 18:50:07 -05:00
super.c hlist: drop the node parameter from iterators 2013-02-27 19:10:24 -08:00
sync.c new helper: file_inode(file) 2013-02-22 23:31:31 -05:00
timerfd.c compat: restore timerfd settime and gettime compat syscalls 2013-03-02 09:35:13 -05:00
utimes.c vfs: allow utimensat() calls to retry once on an ESTALE error 2012-12-20 18:50:08 -05:00
xattr.c vfs: make lremovexattr retry once on ESTALE error 2012-12-20 18:50:11 -05:00
xattr_acl.c userns: Fix posix_acl_file_xattr_userns gid conversion 2012-10-12 13:16:48 -07:00