Re: [PATCH net-next 09/10] net/smc: fix potential panic dues to unprotected smc_llc_srv_add_link()

[Tony Lu <tonylu@linux.alibaba.com>]

On Thu, Aug 11, 2022 at 01:47:40AM +0800, D. Wythe wrote:
> From: "D. Wythe" <alibuda@linux.alibaba.com>
> 
> After we optimize the parallel capability of SMC-R connection
> establishment, there is a certain chance to trigger the
> following panic:
> 
> PID: 5900   TASK: ffff88c1c8af4100  CPU: 1   COMMAND: "kworker/1:48"
>  #0 [ffff9456c1cc79a0] machine_kexec at ffffffff870665b7
>  #1 [ffff9456c1cc79f0] __crash_kexec at ffffffff871b4c7a
>  #2 [ffff9456c1cc7ab0] crash_kexec at ffffffff871b5b60
>  #3 [ffff9456c1cc7ac0] oops_end at ffffffff87026ce7
>  #4 [ffff9456c1cc7ae0] page_fault_oops at ffffffff87075715
>  #5 [ffff9456c1cc7b58] exc_page_fault at ffffffff87ad0654
>  #6 [ffff9456c1cc7b80] asm_exc_page_fault at ffffffff87c00b62
>     [exception RIP: ib_alloc_mr+19]
>     RIP: ffffffffc0c9cce3  RSP: ffff9456c1cc7c38  RFLAGS: 00010202
>     RAX: 0000000000000000  RBX: 0000000000000002  RCX: 0000000000000004
>     RDX: 0000000000000010  RSI: 0000000000000000  RDI: 0000000000000000
>     RBP: ffff88c1ea281d00   R8: 000000020a34ffff   R9: ffff88c1350bbb20
>     R10: 0000000000000000  R11: 0000000000000001  R12: 0000000000000000
>     R13: 0000000000000010  R14: ffff88c1ab040a50  R15: ffff88c1ea281d00
>     ORIG_RAX: ffffffffffffffff  CS: 0010  SS: 0018
>  #7 [ffff9456c1cc7c60] smc_ib_get_memory_region at ffffffffc0aff6df [smc]
>  #8 [ffff9456c1cc7c88] smcr_buf_map_link at ffffffffc0b0278c [smc]
>  #9 [ffff9456c1cc7ce0] __smc_buf_create at ffffffffc0b03586 [smc]
> 
> The reason here is that when the server tries to create a second link,
> smc_llc_srv_add_link() has no protection and may add a new link to
> link group. This breaks the security environment protected by
> llc_conf_mutex.
> 
> Signed-off-by: D. Wythe <alibuda@linux.alibaba.com>

I am curious if this patch can be merged with the previous one? It seems
that this panic is introduced by previous one?

> ---
>  net/smc/af_smc.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/net/smc/af_smc.c b/net/smc/af_smc.c
> index 39dbf39..0b0c53a 100644
> --- a/net/smc/af_smc.c
> +++ b/net/smc/af_smc.c
> @@ -1834,8 +1834,10 @@ static int smcr_serv_conf_first_link(struct smc_sock *smc)
>  	smc_llc_link_active(link);
>  	smcr_lgr_set_type(link->lgr, SMC_LGR_SINGLE);
>  
> +	down_write(&link->lgr->llc_conf_mutex);
>  	/* initial contact - try to establish second link */
>  	smc_llc_srv_add_link(link, NULL);
> +	up_write(&link->lgr->llc_conf_mutex);
>  	return 0;
>  }
>  
> -- 
> 1.8.3.1