linux-sg2042/fs/ext4
Eric W. Biederman 7f78e03513 fs: Limit sys_mount to only request filesystem modules.
Modify the request_module to prefix the file system type with "fs-"
and add aliases to all of the filesystems that can be built as modules
to match.

A common practice is to build all of the kernel code and leave code
that is not commonly needed as modules, with the result that many
users are exposed to any bug anywhere in the kernel.

Looking for filesystems with a fs- prefix limits the pool of possible
modules that can be loaded by mount to just filesystems trivially
making things safer with no real cost.

Using aliases means user space can control the policy of which
filesystem modules are auto-loaded by editing /etc/modprobe.d/*.conf
with blacklist and alias directives.  Allowing simple, safe,
well understood work-arounds to known problematic software.

This also addresses a rare but unfortunate problem where the filesystem
name is not the same as it's module name and module auto-loading
would not work.  While writing this patch I saw a handful of such
cases.  The most significant being autofs that lives in the module
autofs4.

This is relevant to user namespaces because we can reach the request
module in get_fs_type() without having any special permissions, and
people get uncomfortable when a user specified string (in this case
the filesystem type) goes all of the way to request_module.

After having looked at this issue I don't think there is any
particular reason to perform any filtering or permission checks beyond
making it clear in the module request that we want a filesystem
module.  The common pattern in the kernel is to call request_module()
without regards to the users permissions.  In general all a filesystem
module does once loaded is call register_filesystem() and go to sleep.
Which means there is not much attack surface exposed by loading a
filesytem module unless the filesystem is mounted.  In a user
namespace filesystems are not mounted unless .fs_flags = FS_USERNS_MOUNT,
which most filesystems do not set today.

Acked-by: Serge Hallyn <serge.hallyn@canonical.com>
Acked-by: Kees Cook <keescook@chromium.org>
Reported-by: Kees Cook <keescook@google.com>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
2013-03-03 19:36:31 -08:00
..
Kconfig ext4: fix configuration dependencies for ext4 ACLs and security labels 2013-01-06 23:38:44 -05:00
Makefile ext4: Remove CONFIG_EXT4_FS_XATTR 2012-12-10 16:30:43 -05:00
acl.c ext4: fix the number of credits needed for acl ops with inline data 2013-02-09 15:23:03 -05:00
acl.h fs: take the ACL checks to common code 2011-07-25 14:30:23 -04:00
balloc.c ext4: convert number of blocks to clusters properly 2013-03-02 17:18:58 -05:00
bitmap.c ext4: Checksum the block bitmap properly with bigalloc enabled 2012-10-22 00:34:32 -04:00
block_validity.c ext2/3/4: delete unneeded includes of module.h 2012-01-09 13:52:10 +01:00
dir.c Various bug fixes for ext4. The most important is a fix for the new 2013-03-02 19:33:21 -08:00
ext4.h ext4: use percpu counter for extent cache count 2013-03-02 10:27:46 -05:00
ext4_extents.h ext4: remove single extent cache 2013-02-18 00:31:07 -05:00
ext4_jbd2.c ext4: pass context information to jbd2__journal_start() 2013-02-08 21:59:22 -05:00
ext4_jbd2.h ext4: fix the number of credits needed for acl ops with inline data 2013-02-09 15:23:03 -05:00
extents.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
extents_status.c ext4: use percpu counter for extent cache count 2013-03-02 10:27:46 -05:00
extents_status.h ext4: fix extent status tree regression for file systems > 512GB 2013-02-27 14:54:37 -05:00
file.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
fsync.c ext4: fix an incorrect comment about i_mutex 2012-12-25 13:31:52 -05:00
hash.c ext4: reduce one "if" comparison in ext4_dirhash() 2013-02-01 22:33:21 -05:00
ialloc.c ext4: use KERN_WARNING for warning messages 2013-02-14 15:11:41 -05:00
indirect.c more file_inode() open-coded instances 2013-02-27 16:59:05 -05:00
inline.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
inode.c 2 writeback fixes 2013-02-28 13:21:44 -08:00
ioctl.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
mballoc.c ext4: convert number of blocks to clusters properly 2013-03-02 17:18:58 -05:00
mballoc.h ext4: use module parameters instead of debugfs for mballoc_debug 2013-02-09 16:28:20 -05:00
migrate.c ext4: fix the number of credits needed for ext4_ext_migrate() 2013-02-09 12:50:27 -05:00
mmp.c ext4: use unlikely to improve the efficiency of the kernel 2013-01-12 16:28:47 -05:00
move_extent.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
namei.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
page-io.c ext4: fix possible use-after-free with AIO 2013-01-29 22:48:17 -05:00
resize.c ext4: convert number of blocks to clusters properly 2013-03-02 17:18:58 -05:00
super.c fs: Limit sys_mount to only request filesystem modules. 2013-03-03 19:36:31 -08:00
symlink.c ext4: Remove CONFIG_EXT4_FS_XATTR 2012-12-10 16:30:43 -05:00
truncate.h ext4: move common truncate functions to header file 2011-06-27 19:16:04 -04:00
xattr.c ext4: fix xattr block allocation/release with bigalloc 2013-02-18 12:12:07 -05:00
xattr.h ext4: fix the number of credits needed for acl ops with inline data 2013-02-09 15:23:03 -05:00
xattr_security.c Merge branch 'for_linus' into for_linus_merged 2012-01-10 11:54:07 -05:00
xattr_trusted.c ext2/3/4: delete unneeded includes of module.h 2012-01-09 13:52:10 +01:00
xattr_user.c ext2/3/4: delete unneeded includes of module.h 2012-01-09 13:52:10 +01:00