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>

69 files changed, 77 insertions, 12 deletions

diff --git a/arch/ia64/kernel/perfmon.c b/arch/ia64/kernel/perfmon.c
index 433f5e8a2cd1..2eda28414abb 100644
--- a/arch/ia64/kernel/perfmon.c
+++ b/arch/ia64/kernel/perfmon.c
@@ -619,6 +619,7 @@ static struct file_system_type pfm_fs_type = {
 	.mount    = pfmfs_mount,
 	.kill_sb  = kill_anon_super,
 };
+MODULE_ALIAS_FS("pfmfs");
 
 DEFINE_PER_CPU(unsigned long, pfm_syst_info);
 DEFINE_PER_CPU(struct task_struct *, pmu_owner);
diff --git a/arch/powerpc/platforms/cell/spufs/inode.c b/arch/powerpc/platforms/cell/spufs/inode.c
index 863184b182f4..3f3bb4cdbbec 100644
--- a/arch/powerpc/platforms/cell/spufs/inode.c
+++ b/arch/powerpc/platforms/cell/spufs/inode.c
@@ -749,6 +749,7 @@ static struct file_system_type spufs_type = {
 	.mount = spufs_mount,
 	.kill_sb = kill_litter_super,
 };
+MODULE_ALIAS_FS("spufs");
 
 static int __init spufs_init(void)
 {
diff --git a/arch/s390/hypfs/inode.c b/arch/s390/hypfs/inode.c
index 8538015ed4a0..5f7d7ba2874c 100644
--- a/arch/s390/hypfs/inode.c
+++ b/arch/s390/hypfs/inode.c
@@ -456,6 +456,7 @@ static struct file_system_type hypfs_type = {
 	.mount		= hypfs_mount,
 	.kill_sb	= hypfs_kill_super
 };
+MODULE_ALIAS_FS("s390_hypfs");
 
 static const struct super_operations hypfs_s_ops = {
 	.statfs		= simple_statfs,
diff --git a/drivers/firmware/efivars.c b/drivers/firmware/efivars.c
index 7320bf891706..3edade07b249 100644
--- a/drivers/firmware/efivars.c
+++ b/drivers/firmware/efivars.c
@@ -1234,6 +1234,7 @@ static struct file_system_type efivarfs_type = {
 	.mount   = efivarfs_mount,
 	.kill_sb = efivarfs_kill_sb,
 };
+MODULE_ALIAS_FS("efivarfs");
 
 /*
  * Handle negative dentry.
diff --git a/drivers/infiniband/hw/ipath/ipath_fs.c b/drivers/infiniband/hw/ipath/ipath_fs.c
index a479375a8fd8..e0c404bdc4a8 100644
--- a/drivers/infiniband/hw/ipath/ipath_fs.c
+++ b/drivers/infiniband/hw/ipath/ipath_fs.c
@@ -410,6 +410,7 @@ static struct file_system_type ipathfs_fs_type = {
 	.mount =	ipathfs_mount,
 	.kill_sb =	ipathfs_kill_super,
 };
+MODULE_ALIAS_FS("ipathfs");
 
 int __init ipath_init_ipathfs(void)
 {
diff --git a/drivers/infiniband/hw/qib/qib_fs.c b/drivers/infiniband/hw/qib/qib_fs.c
index 644bd6f6467c..f247fc6e6182 100644
--- a/drivers/infiniband/hw/qib/qib_fs.c
+++ b/drivers/infiniband/hw/qib/qib_fs.c
@@ -604,6 +604,7 @@ static struct file_system_type qibfs_fs_type = {
 	.mount =        qibfs_mount,
 	.kill_sb =      qibfs_kill_super,
 };
+MODULE_ALIAS_FS("ipathfs");
 
 int __init qib_init_qibfs(void)
 {
diff --git a/drivers/misc/ibmasm/ibmasmfs.c b/drivers/misc/ibmasm/ibmasmfs.c
index 6673e578b3e9..ce5b75616b45 100644
--- a/drivers/misc/ibmasm/ibmasmfs.c
+++ b/drivers/misc/ibmasm/ibmasmfs.c
@@ -110,6 +110,7 @@ static struct file_system_type ibmasmfs_type = {
 	.mount          = ibmasmfs_mount,
 	.kill_sb        = kill_litter_super,
 };
+MODULE_ALIAS_FS("ibmasmfs");
 
 static int ibmasmfs_fill_super (struct super_block *sb, void *data, int silent)
 {
diff --git a/drivers/mtd/mtdchar.c b/drivers/mtd/mtdchar.c
index 82c06165d3d2..92ab30ab00dc 100644
--- a/drivers/mtd/mtdchar.c
+++ b/drivers/mtd/mtdchar.c
@@ -1238,6 +1238,7 @@ static struct file_system_type mtd_inodefs_type = {
        .mount = mtd_inodefs_mount,
        .kill_sb = kill_anon_super,
 };
+MODULE_ALIAS_FS("mtd_inodefs");
 
 static int __init init_mtdchar(void)
 {
diff --git a/drivers/oprofile/oprofilefs.c b/drivers/oprofile/oprofilefs.c
index 445ffda715ad..7c12d9c2b230 100644
--- a/drivers/oprofile/oprofilefs.c
+++ b/drivers/oprofile/oprofilefs.c
@@ -276,6 +276,7 @@ static struct file_system_type oprofilefs_type = {
 	.mount		= oprofilefs_mount,
 	.kill_sb	= kill_litter_super,
 };
+MODULE_ALIAS_FS("oprofilefs");
 
 
 int __init oprofilefs_register(void)
diff --git a/drivers/staging/ccg/f_fs.c b/drivers/staging/ccg/f_fs.c
index 8adc79d1b402..f6373dade7fb 100644
--- a/drivers/staging/ccg/f_fs.c
+++ b/drivers/staging/ccg/f_fs.c
@@ -1223,6 +1223,7 @@ static struct file_system_type ffs_fs_type = {
 	.mount		= ffs_fs_mount,
 	.kill_sb	= ffs_fs_kill_sb,
 };
+MODULE_ALIAS_FS("functionfs");
 
 
 /* Driver's main init/cleanup functions *************************************/
diff --git a/drivers/usb/gadget/f_fs.c b/drivers/usb/gadget/f_fs.c
index 38388d7844fc..c377ff84bf2c 100644
--- a/drivers/usb/gadget/f_fs.c
+++ b/drivers/usb/gadget/f_fs.c
@@ -1235,6 +1235,7 @@ static struct file_system_type ffs_fs_type = {
 	.mount		= ffs_fs_mount,
 	.kill_sb	= ffs_fs_kill_sb,
 };
+MODULE_ALIAS_FS("functionfs");
 
 
 /* Driver's main init/cleanup functions *************************************/
diff --git a/drivers/usb/gadget/inode.c b/drivers/usb/gadget/inode.c
index 8ac840f25ba9..e2b2e9cf254a 100644
--- a/drivers/usb/gadget/inode.c
+++ b/drivers/usb/gadget/inode.c
@@ -2105,6 +2105,7 @@ static struct file_system_type gadgetfs_type = {
 	.mount		= gadgetfs_mount,
 	.kill_sb	= gadgetfs_kill_sb,
 };
+MODULE_ALIAS_FS("gadgetfs");
 
 /*----------------------------------------------------------------------*/
 
diff --git a/drivers/xen/xenfs/super.c b/drivers/xen/xenfs/super.c
index ec0abb6df3c3..71679875f056 100644
--- a/drivers/xen/xenfs/super.c
+++ b/drivers/xen/xenfs/super.c
@@ -75,6 +75,7 @@ static struct file_system_type xenfs_type = {
 	.mount =	xenfs_mount,
 	.kill_sb =	kill_litter_super,
 };
+MODULE_ALIAS_FS("xenfs");
 
 static int __init xenfs_init(void)
 {
diff --git a/fs/9p/vfs_super.c b/fs/9p/vfs_super.c
index 91dad63e5a2d..2756dcd5de6e 100644
--- a/fs/9p/vfs_super.c
+++ b/fs/9p/vfs_super.c
@@ -365,3 +365,4 @@ struct file_system_type v9fs_fs_type = {
 	.owner = THIS_MODULE,
 	.fs_flags = FS_RENAME_DOES_D_MOVE,
 };
+MODULE_ALIAS_FS("9p");
diff --git a/fs/adfs/super.c b/fs/adfs/super.c
index d57122935793..0ff4bae2c2a2 100644
--- a/fs/adfs/super.c
+++ b/fs/adfs/super.c
@@ -524,6 +524,7 @@ static struct file_system_type adfs_fs_type = {
 	.kill_sb	= kill_block_super,
 	.fs_flags	= FS_REQUIRES_DEV,
 };
+MODULE_ALIAS_FS("adfs");
 
 static int __init init_adfs_fs(void)
 {
diff --git a/fs/affs/super.c b/fs/affs/super.c
index b84dc7352502..45161a832bbc 100644
--- a/fs/affs/super.c
+++ b/fs/affs/super.c
@@ -622,6 +622,7 @@ static struct file_system_type affs_fs_type = {
 	.kill_sb	= kill_block_super,
 	.fs_flags	= FS_REQUIRES_DEV,
 };
+MODULE_ALIAS_FS("affs");
 
 static int __init init_affs_fs(void)
 {
diff --git a/fs/afs/super.c b/fs/afs/super.c
index 7c31ec399575..c4861557e385 100644
--- a/fs/afs/super.c
+++ b/fs/afs/super.c
@@ -45,6 +45,7 @@ struct file_system_type afs_fs_type = {
 	.kill_sb	= afs_kill_super,
 	.fs_flags	= 0,
 };
+MODULE_ALIAS_FS("afs");
 
 static const struct super_operations afs_super_ops = {
 	.statfs		= afs_statfs,
diff --git a/fs/autofs4/init.c b/fs/autofs4/init.c
index cddc74b9cdb2..b3db517e89ec 100644
--- a/fs/autofs4/init.c
+++ b/fs/autofs4/init.c
@@ -26,6 +26,7 @@ static struct file_system_type autofs_fs_type = {
 	.mount		= autofs_mount,
 	.kill_sb	= autofs4_kill_sb,
 };
+MODULE_ALIAS_FS("autofs");
 
 static int __init init_autofs4_fs(void)
 {
diff --git a/fs/befs/linuxvfs.c b/fs/befs/linuxvfs.c
index c8f4e25eb9e2..8615ee89ab55 100644
--- a/fs/befs/linuxvfs.c
+++ b/fs/befs/linuxvfs.c
@@ -951,6 +951,7 @@ static struct file_system_type befs_fs_type = {
 	.kill_sb	= kill_block_super,
 	.fs_flags	= FS_REQUIRES_DEV,	
 };
+MODULE_ALIAS_FS("befs");
 
 static int __init
 init_befs_fs(void)
diff --git a/fs/bfs/inode.c b/fs/bfs/inode.c
index 737aaa3f7090..5e376bb93419 100644
--- a/fs/bfs/inode.c
+++ b/fs/bfs/inode.c
@@ -473,6 +473,7 @@ static struct file_system_type bfs_fs_type = {
 	.kill_sb	= kill_block_super,
 	.fs_flags	= FS_REQUIRES_DEV,
 };
+MODULE_ALIAS_FS("bfs");
 
 static int __init init_bfs_fs(void)
 {
diff --git a/fs/binfmt_misc.c b/fs/binfmt_misc.c
index fecbbf3f8ff2..751df5e4f61a 100644
--- a/fs/binfmt_misc.c
+++ b/fs/binfmt_misc.c
@@ -720,6 +720,7 @@ static struct file_system_type bm_fs_type = {
 	.mount		= bm_mount,
 	.kill_sb	= kill_litter_super,
 };
+MODULE_ALIAS_FS("binfmt_misc");
 
 static int __init init_misc_binfmt(void)
 {
diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 68a29a1ea068..f6b88595f858 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -1558,6 +1558,7 @@ static struct file_system_type btrfs_fs_type = {
 	.kill_sb	= btrfs_kill_super,
 	.fs_flags	= FS_REQUIRES_DEV,
 };
+MODULE_ALIAS_FS("btrfs");
 
 /*
  * used by btrfsctl to scan devices when no FS is mounted
diff --git a/fs/ceph/super.c b/fs/ceph/super.c
index 9fe17c6c2876..6ddc0bca56b2 100644
--- a/fs/ceph/super.c
+++ b/fs/ceph/super.c
@@ -952,6 +952,7 @@ static struct file_system_type ceph_fs_type = {
 	.kill_sb	= ceph_kill_sb,
 	.fs_flags	= FS_RENAME_DOES_D_MOVE,
 };
+MODULE_ALIAS_FS("ceph");
 
 #define _STRINGIFY(x) #x
 #define STRINGIFY(x) _STRINGIFY(x)
diff --git a/fs/coda/inode.c b/fs/coda/inode.c
index dada9d0abede..4dcc0d81a7aa 100644
--- a/fs/coda/inode.c
+++ b/fs/coda/inode.c
@@ -329,4 +329,5 @@ struct file_system_type coda_fs_type = {
 	.kill_sb	= kill_anon_super,
 	.fs_flags	= FS_BINARY_MOUNTDATA,
 };
+MODULE_ALIAS_FS("coda");
 
diff --git a/fs/configfs/mount.c b/fs/configfs/mount.c
index aee0a7ebbd8e..7f26c3cf75ae 100644
--- a/fs/configfs/mount.c
+++ b/fs/configfs/mount.c
@@ -114,6 +114,7 @@ static struct file_system_type configfs_fs_type = {
 	.mount		= configfs_do_mount,
 	.kill_sb	= kill_litter_super,
 };
+MODULE_ALIAS_FS("configfs");
 
 struct dentry *configfs_pin_fs(void)
 {
diff --git a/fs/cramfs/inode.c b/fs/cramfs/inode.c
index 3ceb9ec976e1..35b1c7bd18b7 100644
--- a/fs/cramfs/inode.c
+++ b/fs/cramfs/inode.c
@@ -573,6 +573,7 @@ static struct file_system_type cramfs_fs_type = {
 	.kill_sb	= kill_block_super,
 	.fs_flags	= FS_REQUIRES_DEV,
 };
+MODULE_ALIAS_FS("cramfs");
 
 static int __init init_cramfs_fs(void)
 {
diff --git a/fs/debugfs/inode.c b/fs/debugfs/inode.c
index 0c4f80b447fb..4888cb3fdef7 100644
--- a/fs/debugfs/inode.c
+++ b/fs/debugfs/inode.c
@@ -299,6 +299,7 @@ static struct file_system_type debug_fs_type = {
 	.mount =	debug_mount,
 	.kill_sb =	kill_litter_super,
 };
+MODULE_ALIAS_FS("debugfs");
 
 static struct dentry *__create_file(const char *name, umode_t mode,
 				    struct dentry *parent, void *data,
diff --git a/fs/devpts/inode.c b/fs/devpts/inode.c
index 073d30b9d1ac..79b662985efe 100644
--- a/fs/devpts/inode.c
+++ b/fs/devpts/inode.c
@@ -510,6 +510,7 @@ static struct file_system_type devpts_fs_type = {
 	.fs_flags	= FS_USERNS_MOUNT | FS_USERNS_DEV_MOUNT,
 #endif
 };
+MODULE_ALIAS_FS("devpts");
 
 /*
  * The normal naming convention is simply /dev/pts/<number>; this conforms
diff --git a/fs/ecryptfs/main.c b/fs/ecryptfs/main.c
index 4e0886c9e5c4..e924cf45aad9 100644
--- a/fs/ecryptfs/main.c
+++ b/fs/ecryptfs/main.c
@@ -629,6 +629,7 @@ static struct file_system_type ecryptfs_fs_type = {
 	.kill_sb = ecryptfs_kill_block_super,
 	.fs_flags = 0
 };
+MODULE_ALIAS_FS("ecryptfs");
 
 /**
  * inode_info_init_once
diff --git a/fs/efs/super.c b/fs/efs/super.c
index 2002431ef9a0..c6f57a74a559 100644
--- a/fs/efs/super.c
+++ b/fs/efs/super.c
@@ -33,6 +33,7 @@ static struct file_system_type efs_fs_type = {
 	.kill_sb	= kill_block_super,
 	.fs_flags	= FS_REQUIRES_DEV,
 };
+MODULE_ALIAS_FS("efs");
 
 static struct pt_types sgi_pt_types[] = {
 	{0x00,		"SGI vh"},
diff --git a/fs/exofs/super.c b/fs/exofs/super.c
index 5e59280d42d7..9d9763328734 100644
--- a/fs/exofs/super.c
+++ b/fs/exofs/super.c
@@ -1010,6 +1010,7 @@ static struct file_system_type exofs_type = {
 	.mount          = exofs_mount,
 	.kill_sb        = generic_shutdown_super,
 };
+MODULE_ALIAS_FS("exofs");
 
 static int __init init_exofs(void)
 {
diff --git a/fs/ext2/super.c b/fs/ext2/super.c
index 7f68c8114026..288534920fe5 100644
--- a/fs/ext2/super.c
+++ b/fs/ext2/super.c
@@ -1536,6 +1536,7 @@ static struct file_system_type ext2_fs_type = {
 	.kill_sb	= kill_block_super,
 	.fs_flags	= FS_REQUIRES_DEV,
 };
+MODULE_ALIAS_FS("ext2");
 
 static int __init init_ext2_fs(void)
 {
diff --git a/fs/ext3/super.c b/fs/ext3/super