[PATCH linux-next] mqueue: fix IPC namespace use-after-free

From: Giuseppe Scrivano
Date: Tue Dec 19 2017 - 05:15:10 EST

mqueue_evict_inode() doesn't access the ipc namespace if it was
already freed. It can happen if in a new IPC namespace the inode was
created without a prior mq_open() which creates the vfsmount used to
access the superblock from mq_clear_sbinfo().

Keep a direct pointer to the superblock used by the inodes so we can
correctly reset the reference to the IPC namespace being destroyed.

Bug introduced with 9c583773d03633 ("ipc, mqueue: lazy call
kern_mount_data in new namespaces")

BUG: KASAN: use-after-free in __read_once_size include/linux/compiler.h:183
BUG: KASAN: use-after-free in atomic_read arch/x86/include/asm/atomic.h:27
BUG: KASAN: use-after-free in refcount_inc_not_zero+0x16e/0x180
Read of size 4 at addr ffff8801c51bb200 by task syzkaller711981/3156

CPU: 1 PID: 3156 Comm: syzkaller711981 Not tainted 4.15.0-rc2-mm1+ #39
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:17 [inline]
dump_stack+0x194/0x257 lib/dump_stack.c:53
print_address_description+0x73/0x250 mm/kasan/report.c:252
kasan_report_error mm/kasan/report.c:351 [inline]
kasan_report+0x25b/0x340 mm/kasan/report.c:409
__asan_report_load4_noabort+0x14/0x20 mm/kasan/report.c:429
__read_once_size include/linux/compiler.h:183 [inline]
atomic_read arch/x86/include/asm/atomic.h:27 [inline]
refcount_inc_not_zero+0x16e/0x180 lib/refcount.c:120
refcount_inc+0x15/0x50 lib/refcount.c:153
get_ipc_ns include/linux/ipc_namespace.h:129 [inline]
__get_ns_from_inode ipc/mqueue.c:110 [inline]
get_ns_from_inode ipc/mqueue.c:118 [inline]
mqueue_evict_inode+0x137/0x9c0 ipc/mqueue.c:402
evict+0x481/0x920 fs/inode.c:552
iput_final fs/inode.c:1514 [inline]
iput+0x7b9/0xaf0 fs/inode.c:1541
dentry_unlink_inode+0x4b0/0x5e0 fs/dcache.c:376
__dentry_kill+0x3b7/0x6d0 fs/dcache.c:573
shrink_dentry_list+0x3c5/0xcf0 fs/dcache.c:1020
shrink_dcache_parent+0xba/0x230 fs/dcache.c:1454
do_one_tree+0x15/0x50 fs/dcache.c:1485
shrink_dcache_for_umount+0xbb/0x290 fs/dcache.c:1502
generic_shutdown_super+0xcd/0x540 fs/super.c:424
kill_anon_super fs/super.c:987 [inline]
kill_litter_super+0x72/0x90 fs/super.c:997
deactivate_locked_super+0x88/0xd0 fs/super.c:312
deactivate_super+0x141/0x1b0 fs/super.c:343
cleanup_mnt+0xb2/0x150 fs/namespace.c:1173
__cleanup_mnt+0x16/0x20 fs/namespace.c:1180
task_work_run+0x199/0x270 kernel/task_work.c:113
exit_task_work include/linux/task_work.h:22 [inline]
do_exit+0x9bb/0x1ae0 kernel/exit.c:869
do_group_exit+0x149/0x400 kernel/exit.c:972
SYSC_exit_group kernel/exit.c:983 [inline]
SyS_exit_group+0x1d/0x20 kernel/exit.c:981
RIP: 0033:0x440729
RSP: 002b:00007ffd090ef228 EFLAGS: 00000206 ORIG_RAX: 00000000000000e7
RAX: ffffffffffffffda RBX: 0030656c69662f2e RCX: 0000000000440729
RDX: 0000000000440729 RSI: 0000000000000000 RDI: 0000000000000001
RBP: 00000000006cb018 R08: 0000000000000000 R09: 00000000004002c8
R10: 0000000000000000 R11: 0000000000000206 R12: 0000000000401bf0
R13: 0000000000401c80 R14: 0000000000000000 R15: 0000000000000000

Allocated by task 3156:
save_stack+0x43/0xd0 mm/kasan/kasan.c:447
set_track mm/kasan/kasan.c:459 [inline]
kasan_kmalloc+0xad/0xe0 mm/kasan/kasan.c:551
kmem_cache_alloc_trace+0x136/0x750 mm/slab.c:3614
kmalloc include/linux/slab.h:516 [inline]
create_ipc_ns ipc/namespace.c:45 [inline]
copy_ipcs+0x1b3/0x520 ipc/namespace.c:96
create_new_namespaces+0x278/0x880 kernel/nsproxy.c:87
unshare_nsproxy_namespaces+0xae/0x1e0 kernel/nsproxy.c:206
SYSC_unshare kernel/fork.c:2421 [inline]
SyS_unshare+0x653/0xfa0 kernel/fork.c:2371

Freed by task 3156:
save_stack+0x43/0xd0 mm/kasan/kasan.c:447
set_track mm/kasan/kasan.c:459 [inline]
kasan_slab_free+0x71/0xc0 mm/kasan/kasan.c:524
__cache_free mm/slab.c:3492 [inline]
kfree+0xca/0x250 mm/slab.c:3807
free_ipc_ns ipc/namespace.c:139 [inline]
put_ipc_ns+0x112/0x150 ipc/namespace.c:164
free_nsproxy+0xc0/0x1f0 kernel/nsproxy.c:180
switch_task_namespaces+0x9d/0xc0 kernel/nsproxy.c:229
exit_task_namespaces+0x17/0x20 kernel/nsproxy.c:234
do_exit+0x9b6/0x1ae0 kernel/exit.c:868
do_group_exit+0x149/0x400 kernel/exit.c:972
SYSC_exit_group kernel/exit.c:983 [inline]
SyS_exit_group+0x1d/0x20 kernel/exit.c:981

The buggy address belongs to the object at ffff8801c51bb200
which belongs to the cache kmalloc-2048 of size 2048
The buggy address is located 0 bytes inside of
2048-byte region [ffff8801c51bb200, ffff8801c51bba00)
The buggy address belongs to the page:
page:000000007764ba6d count:1 mapcount:0 mapping:000000002c36623f index:0x0
compound_mapcount: 0
flags: 0x2fffc0000008100(slab|head)
raw: 02fffc0000008100 ffff8801c51ba100 0000000000000000 0000000100000003
raw: ffffea000715d320 ffff8801dac01950 ffff8801dac00c40 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff8801c51bb100: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff8801c51bb180: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> ffff8801c51bb200: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff8801c51bb280: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff8801c51bb300: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb

Reported-by: syzbot <syzkaller@xxxxxxxxxxxxxxxx>
Signed-off-by: Giuseppe Scrivano <gscrivan@xxxxxxxxxx>
include/linux/ipc_namespace.h | 3 ++-
ipc/mqueue.c | 6 ++++--
2 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/include/linux/ipc_namespace.h b/include/linux/ipc_namespace.h
index 554e31494f69..29ae2ede7602 100644
--- a/include/linux/ipc_namespace.h
+++ b/include/linux/ipc_namespace.h
@@ -52,7 +52,8 @@ struct ipc_namespace {
struct notifier_block ipcns_nb;

/* The kern_mount of the mqueuefs sb. We take a ref on it */
- struct vfsmount *mq_mnt;
+ struct vfsmount *mq_mnt;
+ struct super_block *mq_sb;

/* # queues in this ns, protected by mq_lock */
unsigned int mq_queues_count;
diff --git a/ipc/mqueue.c b/ipc/mqueue.c
index 36f177dcb39a..d664c0b0f075 100644
--- a/ipc/mqueue.c
+++ b/ipc/mqueue.c
@@ -341,6 +341,7 @@ static int mqueue_fill_super(struct super_block *sb, void *data, int silent)
sb->s_root = d_make_root(inode);
if (!sb->s_root)
return -ENOMEM;
+ ns->mq_sb = sb;
return 0;

@@ -1554,6 +1555,7 @@ int mq_init_ns(struct ipc_namespace *ns, bool mount)
ns->mq_msg_max = DFLT_MSGMAX;
ns->mq_msgsize_max = DFLT_MSGSIZEMAX;
ns->mq_msg_default = DFLT_MSG;
+ ns->mq_sb = NULL;
ns->mq_msgsize_default = DFLT_MSGSIZE;

if (!mount)
@@ -1573,8 +1575,8 @@ int mq_init_ns(struct ipc_namespace *ns, bool mount)

void mq_clear_sbinfo(struct ipc_namespace *ns)
- if (ns->mq_mnt)
- ns->mq_mnt->mnt_sb->s_fs_info = NULL;
+ if (ns->mq_sb)
+ ns->mq_sb->s_fs_info = NULL;

void mq_put_mnt(struct ipc_namespace *ns)