linux-sg2042/fs/nfsd
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 fs/nfsd: remove depends on CONFIG_EXPERIMENTAL 2013-01-21 14:39:05 -08:00
Makefile NFSD: Added fault injection 2011-11-07 21:10:47 -05:00
acl.h nfsd: Remove declaration of nonexistent nfs4_acl_permisison 2013-02-13 06:15:35 -08:00
auth.c nfsd: Properly compare and initialize kuids and kgids 2013-02-13 06:16:09 -08:00
auth.h nfsd: Remove nfsd_luid, nfsd_lgid, nfsd_ruid and nfsd_rgid 2013-02-13 06:15:51 -08:00
cache.h nfsd: keep a checksum of the first 256 bytes of request 2013-02-08 16:02:26 -05:00
current_stateid.h nfsd41: use current stateid by value 2012-02-15 11:20:45 -05:00
export.c Merge branch 'for-3.9' of git://linux-nfs.org/~bfields/linux 2013-02-28 18:02:55 -08:00
fault_inject.c Merge branch 'for-3.9' of git://linux-nfs.org/~bfields/linux 2013-02-28 18:02:55 -08:00
idmap.h nfsd: Convert idmap to use kuids and kgids 2013-02-13 06:15:49 -08:00
lockd.c nfsd: Remove deprecated nfsctl system call and related code. 2011-07-15 18:58:42 -04:00
netns.h nfsd: make NFSd service structure allocated per net 2012-12-10 16:25:39 -05:00
nfs2acl.c nfsd: handle vfs_getattr errors in acl protocol 2013-02-26 02:46:09 -05:00
nfs3acl.c nfsd4: cleanup: replace rq_resused count by rq_next_page pointer 2012-12-17 22:00:16 -05:00
nfs3proc.c switch vfs_getattr() to struct path 2013-02-26 02:46:08 -05:00
nfs3xdr.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
nfs4acl.c nfsd: Handle kuids and kgids in the nfs4acl to posix_acl conversion 2013-02-13 06:16:06 -08:00
nfs4callback.c nfsd: make NFSv4 lease time per net 2012-11-28 10:39:46 -05:00
nfs4idmap.c Merge branch 'for-3.9' of git://linux-nfs.org/~bfields/linux 2013-02-28 18:02:55 -08:00
nfs4proc.c nfsd4: simplify nfsd4_encode_fattr interface slightly 2013-01-23 18:17:35 -05:00
nfs4recover.c Merge branch 'for-3.9' of git://linux-nfs.org/~bfields/linux 2013-02-28 18:02:55 -08:00
nfs4state.c Merge branch 'for-3.9' of git://linux-nfs.org/~bfields/linux 2013-02-28 18:02:55 -08:00
nfs4xdr.c Merge branch 'for-3.9' of git://linux-nfs.org/~bfields/linux 2013-02-28 18:02:55 -08:00
nfscache.c Merge branch 'for-3.9' of git://linux-nfs.org/~bfields/linux 2013-02-28 18:02:55 -08:00
nfsctl.c fs: Limit sys_mount to only request filesystem modules. 2013-03-03 19:36:31 -08:00
nfsd.h fs/nfsd: change type of max_delegations, nfsd_drc_max_mem and nfsd_drc_mem_used 2013-02-23 17:50:22 -08:00
nfsfh.c exportfs: add FILEID_INVALID to indicate invalid fid_type 2012-11-07 19:22:30 -05:00
nfsfh.h fs: propagate umode_t, misc bits 2012-01-03 22:55:10 -05:00
nfsproc.c switch vfs_getattr() to struct path 2013-02-26 02:46:08 -05:00
nfssvc.c Merge branch 'for-3.9' of git://linux-nfs.org/~bfields/linux 2013-02-28 18:02:55 -08:00
nfsxdr.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
state.h nfsd: Modify nfsd4_cb_sec to use kuids and kgids 2013-02-13 06:16:07 -08:00
stats.c SUNRPC: register service stats /proc entries in passed network namespace context 2012-01-31 19:28:18 -05:00
vfs.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
vfs.h switch vfs_getattr() to struct path 2013-02-26 02:46:08 -05:00
xdr.h nfsd: handle vfs_getattr errors in acl protocol 2013-02-26 02:46:09 -05:00
xdr3.h nfsd: handle vfs_getattr errors in acl protocol 2013-02-26 02:46:09 -05:00
xdr4.h nfsd4: simplify nfsd4_encode_fattr interface slightly 2013-01-23 18:17:35 -05:00