Re: [PATCH net] net/smc: avoid recursive sk_callback_lock in listen data_ready

[Mahanta Jambigi]

On 17/06/26 8:58 pm, Runyu Xiao wrote:
> smc_listen() installs smc_clcsock_data_ready() as the underlying TCP
> listen socket's sk_data_ready callback.  smc_clcsock_data_ready() then
> immediately takes sk_callback_lock before looking up the SMC listener and
> queuing smc_tcp_listen_work().
> 
> That is unsafe once the TCP listen socket is leaving TCP_LISTEN.  The TCP
> close/flush path can run the installed sk_data_ready callback with
> sk_callback_lock already held, so entering smc_clcsock_data_ready() again
> tries to take the same rwlock recursively in the same thread.  The nvmet

Could you provide me the exact call stack showing recursive lock? Also
help me with the nvmet commit details.

> TCP listener had to make the same state check before taking
> sk_callback_lock for this reason.
> 
> This issue was found by our static analysis tool and then manually
> reviewed against the current tree.
> 
> The grounded PoC kept the SMC listen callback installation path:
> 
>   smc_listen()
>   smc_clcsock_replace_cb()
>   sk_data_ready = smc_clcsock_data_ready()
> 
> It then modeled the close/flush carrier that invokes the installed
> sk_data_ready callback while sk_callback_lock is already held.  Lockdep
> reported the same-thread recursive acquisition:
> 
>   WARNING: possible recursive locking detected
>   smc_clcsock_data_ready+0xa/0x4d [vuln_msv]
>   smc_close_flush_work+0x1f/0x30 [vuln_msv]
>   *** DEADLOCK ***
> 
> Return before taking sk_callback_lock when the underlying TCP socket is no
> longer in TCP_LISTEN.  In that state there is no listen accept work to
> queue for SMC, and avoiding the callback lock mirrors the fix used by the
> TCP nvmet listener.
> 
> Fixes: 0558226cebee ("net/smc: Fix slab-out-of-bounds issue in fallback")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Runyu Xiao <runyu.xiao@xxxxxxxxxx>
> ---
>  net/smc/af_smc.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/net/smc/af_smc.c b/net/smc/af_smc.c
> index 6421c2e1c84d..1af4e3c333ff 100644
> --- a/net/smc/af_smc.c
> +++ b/net/smc/af_smc.c
> @@ -2631,6 +2631,9 @@ static void smc_clcsock_data_ready(struct sock *listen_clcsock)
>  {
>  	struct smc_sock *lsmc;
>  
> +	if (READ_ONCE(listen_clcsock->sk_state) != TCP_LISTEN)

Is *TCP_LISTEN* check sufficient? What about *TCP_SYN_RECV* or
*TCP_ESTABLISHED*?

> +		return;
> +
>  	read_lock_bh(&listen_clcsock->sk_callback_lock);
>  	lsmc = smc_clcsock_user_data(listen_clcsock);
>  	if (!lsmc)