linux/fs/gfs2
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
..
acl.c gfs2: Use uid_eq and gid_eq where appropriate 2013-02-13 06:15:10 -08:00
acl.h fs: take the ACL checks to common code 2011-07-25 14:30:23 -04:00
aops.c GFS2: Use ->writepages for ordered writes 2013-01-29 10:29:17 +00:00
bmap.c Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace 2013-02-25 16:00:49 -08:00
bmap.h GFS2: New truncate sequence 2010-09-20 11:18:16 +01:00
dentry.c stop passing nameidata * to ->d_revalidate() 2012-07-14 16:34:14 +04:00
dir.c Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace 2013-02-25 16:00:49 -08:00
dir.h GFS2: Add readahead to sequential directory traversal 2011-11-08 09:52:12 +00:00
export.c fs: encode_fh: return FILEID_INVALID if invalid fid_type 2013-02-26 02:46:10 -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
gfs2.h [GFS2] Remove remote lock dropping code 2008-06-27 09:39:44 +01:00
glock.c GFS2: Split glock lru processing into two parts 2013-02-01 20:36:03 +00:00
glock.h GFS2: Review bug traps in glops.c 2012-11-07 13:31:07 +00:00
glops.c gfs2: Convert uids and gids between dinodes and vfs inodes. 2013-02-13 06:15:11 -08:00
glops.h GFS2: Fix AIL flush issue during fsync 2011-10-21 12:39:41 +01:00
incore.h Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace 2013-02-25 16:00:49 -08:00
inode.c Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace 2013-02-25 16:00:49 -08:00
inode.h GFS2: Remove unused argument from gfs2_internal_read 2012-04-24 16:44:37 +01:00
Kconfig GFS2: use depends instead of select in kconfig 2012-03-26 09:18:02 +01:00
lock_dlm.c GFS2: fix skip unlock condition 2013-01-28 09:49:15 +00:00
log.c GFS2: Use ->writepages for ordered writes 2013-01-29 10:29:17 +00:00
log.h GFS2: Use ->writepages for ordered writes 2013-01-29 10:29:17 +00:00
lops.c GFS2: Copy gfs2_trans_add_bh into new data/meta functions 2013-01-29 10:28:28 +00:00
lops.h GFS2: Merge gfs2_attach_bufdata() into trans.c 2013-01-29 10:28:44 +00:00
main.c GFS2: Fold quota data into the reservations struct 2012-06-06 11:20:22 +01:00
Makefile GFS2: Rename ops_inode.c to inode.c 2011-05-10 13:12:49 +01:00
meta_io.c GFS2: Merge gfs2_attach_bufdata() into trans.c 2013-01-29 10:28:44 +00:00
meta_io.h GFS2: Merge gfs2_attach_bufdata() into trans.c 2013-01-29 10:28:44 +00:00
ops_fstype.c fs: Limit sys_mount to only request filesystem modules. 2013-03-03 19:36:31 -08:00
quota.c Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace 2013-02-25 16:00:49 -08:00
quota.h gfs2: Use kuid_t and kgid_t types where appropriate. 2013-02-13 06:15:09 -08:00
recovery.c GFS2: fail mount if journal recovery fails 2012-01-11 09:24:48 +00:00
recovery.h gfs2: use workqueue instead of slow-work 2010-07-23 13:14:25 +02:00
rgrp.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
rgrp.h GFS2: Add Orlov allocator 2012-11-07 13:33:17 +00:00
super.c Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace 2013-02-25 16:00:49 -08:00
super.h GFS2: Clean up freeze code 2013-01-29 10:29:05 +00:00
sys.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
sys.h GFS2: dlm based recovery coordination 2012-01-11 09:23:05 +00:00
trace_gfs2.h GFS2: don't reference inode's glock during block allocation trace 2012-11-16 14:21:48 +00:00
trans.c GFS2: Use ->writepages for ordered writes 2013-01-29 10:29:17 +00:00
trans.h GFS2: Split gfs2_trans_add_bh() into two 2013-01-29 10:28:04 +00:00
util.c GFS2: Reinstate withdraw ack system 2013-02-13 12:21:40 +00:00
util.h GFS2: Fix error handling when reading an invalid block from the journal 2012-06-06 11:27:49 +01:00
xattr.c Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace 2013-02-25 16:00:49 -08:00
xattr.h sanitize xattr handler prototypes 2009-12-16 12:16:49 -05:00