Re: [PATCH v3] net/smc: fix refcount bug in sk_psock_get (2)

[Wen Gu <guwen@linux.alibaba.com>]

On 2022/8/3 16:03, Hawkins Jiawei wrote:
> Syzkaller reports refcount bug as follows:
> ------------[ cut here ]------------
> refcount_t: saturated; leaking memory.
> WARNING: CPU: 1 PID: 3605 at lib/refcount.c:19 refcount_warn_saturate+0xf4/0x1e0 lib/refcount.c:19
> Modules linked in:
> CPU: 1 PID: 3605 Comm: syz-executor208 Not tainted 5.18.0-syzkaller-03023-g7e062cda7d90 #0
>   <TASK>
>   __refcount_add_not_zero include/linux/refcount.h:163 [inline]
>   __refcount_inc_not_zero include/linux/refcount.h:227 [inline]
>   refcount_inc_not_zero include/linux/refcount.h:245 [inline]
>   sk_psock_get+0x3bc/0x410 include/linux/skmsg.h:439
>   tls_data_ready+0x6d/0x1b0 net/tls/tls_sw.c:2091
>   tcp_data_ready+0x106/0x520 net/ipv4/tcp_input.c:4983
>   tcp_data_queue+0x25f2/0x4c90 net/ipv4/tcp_input.c:5057
>   tcp_rcv_state_process+0x1774/0x4e80 net/ipv4/tcp_input.c:6659
>   tcp_v4_do_rcv+0x339/0x980 net/ipv4/tcp_ipv4.c:1682
>   sk_backlog_rcv include/net/sock.h:1061 [inline]
>   __release_sock+0x134/0x3b0 net/core/sock.c:2849
>   release_sock+0x54/0x1b0 net/core/sock.c:3404
>   inet_shutdown+0x1e0/0x430 net/ipv4/af_inet.c:909
>   __sys_shutdown_sock net/socket.c:2331 [inline]
>   __sys_shutdown_sock net/socket.c:2325 [inline]
>   __sys_shutdown+0xf1/0x1b0 net/socket.c:2343
>   __do_sys_shutdown net/socket.c:2351 [inline]
>   __se_sys_shutdown net/socket.c:2349 [inline]
>   __x64_sys_shutdown+0x50/0x70 net/socket.c:2349
>   do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>   do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
>   entry_SYSCALL_64_after_hwframe+0x46/0xb0
>   </TASK>
> 
> During SMC fallback process in connect syscall, kernel will
> replaces TCP with SMC. In order to forward wakeup
> smc socket waitqueue after fallback, kernel will sets
> clcsk->sk_user_data to origin smc socket in
> smc_fback_replace_callbacks().
> 
> Later, in shutdown syscall, kernel will calls
> sk_psock_get(), which treats the clcsk->sk_user_data
> as psock type, triggering the refcnt warning.
> 
> So, the root cause is that smc and psock, both will use
> sk_user_data field. So they will mismatch this field
> easily.
> 
> This patch solves it by using another bit(defined as
> SK_USER_DATA_PSOCK) in PTRMASK, to mark whether
> sk_user_data points to a psock object or not.
> This patch depends on a PTRMASK introduced in commit f1ff5ce2cd5e
> ("net, sk_msg: Clear sk_user_data pointer on clone if tagged").
> 
> Reported-and-tested-by: syzbot+5f26f85569bd179c18ce@syzkaller.appspotmail.com
> Suggested-by: Jakub Kicinski <kuba@kernel.org>
> Acked-by: Wen Gu <guwen@linux.alibaba.com>
> Signed-off-by: Hawkins Jiawei <yin31149@gmail.com>
> ---
> v2 -> v3:
>    - use SK_USER_DATA_PSOCK instead of SK_USER_DATA_NOTPSOCK
> to patch the bug
>    - refactor the code on assigning to sk_user_data field
> in psock part
>    - refactor the code on getting and setting the flag
> with sk_user_data field
> 
> v1 -> v2:
>    - add bit in PTRMASK to patch the bug
> 
>   include/linux/skmsg.h |  2 +-
>   include/net/sock.h    | 58 +++++++++++++++++++++++++++++++------------
>   net/core/skmsg.c      |  3 ++-
>   3 files changed, 45 insertions(+), 18 deletions(-)
> 

Hi Hawkins,

Since the fix v3 doesn't involved smc codes any more, I wonder if it's still
appropriate to use 'net/smc:' in subject?

Cheers,
Wen Gu