linux/fs/f2fs
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 f2fs: avoid null dereference in f2fs_acl_from_disk 2013-01-04 09:46:27 +09:00
acl.h f2fs: adjust kernel coding style 2012-12-11 13:43:42 +09:00
checkpoint.c f2fs: clarify and enhance the f2fs_gc flow 2013-02-12 07:15:02 +09:00
data.c f2fs: support swapfile 2013-01-22 10:48:58 +09:00
debug.c f2fs: add device name in debugfs 2013-02-12 07:15:01 +09:00
dir.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
f2fs.h Merge branch 'f2fs' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs into dev 2013-02-12 07:17:20 +09:00
file.c more file_inode() open-coded instances 2013-02-27 16:59:05 -05:00
gc.c f2fs: fix calculation of max. gc cost in the SSR case 2013-02-12 07:15:02 +09:00
gc.h f2fs: clarify and enhance the f2fs_gc flow 2013-02-12 07:15:02 +09:00
hash.c f2fs: unify string length declarations and usage 2012-12-28 11:27:53 +09:00
inode.c f2fs: avoid balanc_fs during evict_inode 2013-02-12 07:15:01 +09:00
Kconfig f2fs: resolve build failures 2012-12-11 13:43:43 +09:00
Makefile f2fs: update Kconfig and Makefile 2012-12-11 13:43:42 +09:00
namei.c f2fs: unify string length declarations and usage 2012-12-28 11:27:53 +09:00
node.c f2fs: avoid build warning 2013-02-12 07:28:55 +09:00
node.h f2fs: adjust kernel coding style 2012-12-11 13:43:42 +09:00
recovery.c Merge branch 'f2fs' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs into dev 2013-02-12 07:17:20 +09:00
segment.c f2fs: clarify and enhance the f2fs_gc flow 2013-02-12 07:15:02 +09:00
segment.h f2fs: clarify and enhance the f2fs_gc flow 2013-02-12 07:15:02 +09:00
super.c fs: Limit sys_mount to only request filesystem modules. 2013-03-03 19:36:31 -08:00
xattr.c f2fs: add f2fs_balance_fs in several interfaces 2013-01-11 15:09:17 +09:00
xattr.h f2fs: adjust kernel coding style 2012-12-11 13:43:42 +09:00