Re: [PATCH net v2] net/smc: fix illegal rmb_desc access in SMC-D connection dump

[Wenjia Zhang]

On 18.01.24 05:32, Wen Gu wrote:
> A crash was found when dumping SMC-D connections. It can be reproduced
> by following steps:
>
> - run nginx/wrk test:
>    smc_run nginx
>    smc_run wrk -t 16 -c 1000 -d <duration> -H 'Connection: Close' <URL>
>
> - continuously dump SMC-D connections in parallel:
>    watch -n 1 'smcss -D'
>
>   BUG: kernel NULL pointer dereference, address: 0000000000000030
>   CPU: 2 PID: 7204 Comm: smcss Kdump: loaded Tainted: G	E      6.7.0+ #55
>   RIP: 0010:__smc_diag_dump.constprop.0+0x5e5/0x620 [smc_diag]
>   Call Trace:
>    <TASK>
>    ? __die+0x24/0x70
>    ? page_fault_oops+0x66/0x150
>    ? exc_page_fault+0x69/0x140
>    ? asm_exc_page_fault+0x26/0x30
>    ? __smc_diag_dump.constprop.0+0x5e5/0x620 [smc_diag]
>    ? __kmalloc_node_track_caller+0x35d/0x430
>    ? __alloc_skb+0x77/0x170
>    smc_diag_dump_proto+0xd0/0xf0 [smc_diag]
>    smc_diag_dump+0x26/0x60 [smc_diag]
>    netlink_dump+0x19f/0x320
>    __netlink_dump_start+0x1dc/0x300
>    smc_diag_handler_dump+0x6a/0x80 [smc_diag]
>    ? __pfx_smc_diag_dump+0x10/0x10 [smc_diag]
>    sock_diag_rcv_msg+0x121/0x140
>    ? __pfx_sock_diag_rcv_msg+0x10/0x10
>    netlink_rcv_skb+0x5a/0x110
>    sock_diag_rcv+0x28/0x40
>    netlink_unicast+0x22a/0x330
>    netlink_sendmsg+0x1f8/0x420
>    __sock_sendmsg+0xb0/0xc0
>    ____sys_sendmsg+0x24e/0x300
>    ? copy_msghdr_from_user+0x62/0x80
>    ___sys_sendmsg+0x7c/0xd0
>    ? __do_fault+0x34/0x160
>    ? do_read_fault+0x5f/0x100
>    ? do_fault+0xb0/0x110
>    ? __handle_mm_fault+0x2b0/0x6c0
>    __sys_sendmsg+0x4d/0x80
>    do_syscall_64+0x69/0x180
>    entry_SYSCALL_64_after_hwframe+0x6e/0x76
>
> It is possible that the connection is in process of being established
> when we dump it. Assumed that the connection has been registered in a
> link group by smc_conn_create() but the rmb_desc has not yet been
> initialized by smc_buf_create(), thus causing the illegal access to
> conn->rmb_desc. So fix it by checking before dump.
>
> Fixes: 4b1b7d3b30a6 ("net/smc: add SMC-D diag support")
> Signed-off-by: Wen Gu <guwen@xxxxxxxxxxxxxxxxx>
> ---
> v2->v1: corrected the commit in Fixes tag.
> (https://lore.kernel.org/netdev/20240117122749.63785-1-guwen@xxxxxxxxxxxxxxxxx/)
>
>   net/smc/smc_diag.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/net/smc/smc_diag.c b/net/smc/smc_diag.c
> index 52f7c4f1e767..5a33908015f3 100644
> --- a/net/smc/smc_diag.c
> +++ b/net/smc/smc_diag.c
> @@ -164,7 +164,7 @@ static int __smc_diag_dump(struct sock *sk, struct sk_buff *skb,
>   	}
>   	if (smc_conn_lgr_valid(&smc->conn) && smc->conn.lgr->is_smcd &&
>   	    (req->diag_ext & (1 << (SMC_DIAG_DMBINFO - 1))) &&
> -	    !list_empty(&smc->conn.lgr->list)) {
> +	    !list_empty(&smc->conn.lgr->list) && smc->conn.rmb_desc) {
>   		struct smc_connection *conn = &smc->conn;
>   		struct smcd_diag_dmbinfo dinfo;
>   		struct smcd_dev *smcd = conn->lgr->smcd;

That sounds reasonable to me! Thank you for the fix!

Reviewed-by: Wenjia Zhang <wenjia@xxxxxxxxxxxxx>