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Subject[PATCH 4.20 07/32] net: crypto set sk to NULL when af_alg_release.
Date
4.20-stable review patch.  If anyone has any objections, please let me know.

------------------

[ Upstream commit 9060cb719e61b685ec0102574e10337fa5f445ea ]

KASAN has found use-after-free in sockfs_setattr.
The existed commit 6d8c50dcb029 ("socket: close race condition between sock_close()
and sockfs_setattr()") is to fix this simillar issue, but it seems to ignore
that crypto module forgets to set the sk to NULL after af_alg_release.

KASAN report details as below:
BUG: KASAN: use-after-free in sockfs_setattr+0x120/0x150
Write of size 4 at addr ffff88837b956128 by task syz-executor0/4186

CPU: 2 PID: 4186 Comm: syz-executor0 Not tainted xxx + #1
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
1.10.2-1ubuntu1 04/01/2014
Call Trace:
dump_stack+0xca/0x13e
print_address_description+0x79/0x330
? vprintk_func+0x5e/0xf0
kasan_report+0x18a/0x2e0
? sockfs_setattr+0x120/0x150
sockfs_setattr+0x120/0x150
? sock_register+0x2d0/0x2d0
notify_change+0x90c/0xd40
? chown_common+0x2ef/0x510
chown_common+0x2ef/0x510
? chmod_common+0x3b0/0x3b0
? __lock_is_held+0xbc/0x160
? __sb_start_write+0x13d/0x2b0
? __mnt_want_write+0x19a/0x250
do_fchownat+0x15c/0x190
? __ia32_sys_chmod+0x80/0x80
? trace_hardirqs_on_thunk+0x1a/0x1c
__x64_sys_fchownat+0xbf/0x160
? lockdep_hardirqs_on+0x39a/0x5e0
do_syscall_64+0xc8/0x580
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x462589
Code: f7 d8 64 89 02 b8 ff ff ff ff c3 66 0f 1f 44 00 00 48 89 f8 48 89
f7 48 89 d6 48 89
ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3
48 c7 c1 bc ff ff
ff f7 d8 64 89 01 48
RSP: 002b:00007fb4b2c83c58 EFLAGS: 00000246 ORIG_RAX: 0000000000000104
RAX: ffffffffffffffda RBX: 000000000072bfa0 RCX: 0000000000462589
RDX: 0000000000000000 RSI: 00000000200000c0 RDI: 0000000000000007
RBP: 0000000000000005 R08: 0000000000001000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007fb4b2c846bc
R13: 00000000004bc733 R14: 00000000006f5138 R15: 00000000ffffffff

Allocated by task 4185:
kasan_kmalloc+0xa0/0xd0
__kmalloc+0x14a/0x350
sk_prot_alloc+0xf6/0x290
sk_alloc+0x3d/0xc00
af_alg_accept+0x9e/0x670
hash_accept+0x4a3/0x650
__sys_accept4+0x306/0x5c0
__x64_sys_accept4+0x98/0x100
do_syscall_64+0xc8/0x580
entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 4184:
__kasan_slab_free+0x12e/0x180
kfree+0xeb/0x2f0
__sk_destruct+0x4e6/0x6a0
sk_destruct+0x48/0x70
__sk_free+0xa9/0x270
sk_free+0x2a/0x30
af_alg_release+0x5c/0x70
__sock_release+0xd3/0x280
sock_close+0x1a/0x20
__fput+0x27f/0x7f0
task_work_run+0x136/0x1b0
exit_to_usermode_loop+0x1a7/0x1d0
do_syscall_64+0x461/0x580
entry_SYSCALL_64_after_hwframe+0x49/0xbe

Syzkaller reproducer:
r0 = perf_event_open(&(0x7f0000000000)={0x0, 0x70, 0x0, 0x0, 0x0, 0x0,
0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0,
0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0,
0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, @perf_config_ext}, 0x0, 0x0,
0xffffffffffffffff, 0x0)
r1 = socket$alg(0x26, 0x5, 0x0)
getrusage(0x0, 0x0)
bind(r1, &(0x7f00000001c0)=@alg={0x26, 'hash\x00', 0x0, 0x0,
'sha256-ssse3\x00'}, 0x80)
r2 = accept(r1, 0x0, 0x0)
r3 = accept4$unix(r2, 0x0, 0x0, 0x0)
r4 = dup3(r3, r0, 0x0)
fchownat(r4, &(0x7f00000000c0)='\x00', 0x0, 0x0, 0x1000)

Fixes: 6d8c50dcb029 ("socket: close race condition between sock_close() and sockfs_setattr()")
Signed-off-by: Mao Wenan <maowenan@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
crypto/af_alg.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/crypto/af_alg.c b/crypto/af_alg.c
index 17eb09d222ff4..ec78a04eb136e 100644
--- a/crypto/af_alg.c
+++ b/crypto/af_alg.c
@@ -122,8 +122,10 @@ static void alg_do_release(const struct af_alg_type *type, void *private)

int af_alg_release(struct socket *sock)
{
- if (sock->sk)
+ if (sock->sk) {
sock_put(sock->sk);
+ sock->sk = NULL;
+ }
return 0;
}
EXPORT_SYMBOL_GPL(af_alg_release);
--
2.19.1


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