Re: [PATCH v3 1/3] net/smc: bound the wire-controlled producer cursor to the RMB

[Dust Li]

On 2026-06-18 22:11:05, Bryam Vargas wrote:
>On Thu, 18 Jun 2026 22:29:20 +0800, Dust Li wrote:
>> once we detect that the peer is misbehaving, I think the right action is
>> to abort the connection and record the event, rather than silently clamp.
>[...]
>>         u32 prod_count = ntohs(cdc->prod.count);
>> ...
>>             cdc->prod.wrap > 1 || cdc->cons.wrap > 1) {
>
>Thanks for taking a look, Dust. I'm on board with the direction for net-next --
>aborting and recording a bad CDC is cleaner than clamping something we already know
>we can't trust, and as you say, the clamp just papers over the peer bug. So: minimal
>clamp stays for -stable, and net-next gets the wire-boundary check + abort (through
>abort_work, with an smc_stats counter and a ratelimited warn).

That's greate. Then I think we can move on in this direction.

>
>A few things I ran into on the check itself, though:
>
>- count is __be32, so it wants ntohl() rather than ntohs() -- ntohs() ends up reading
>  the wrong half.

Right

>
>- I'd drop the wrap > 1 tests. wrap is a free-running counter (smc_curs_add does
>  wrap++), so a connection that legitimately wraps its RMB ends up with wrap > 1; and
>  since it's a __be16 read raw, on little-endian wrap==1 already reads as 0x0100 and
>  we'd abort on the very first wrap. I don't think there's a sane upper bound to put
>  on wrap.

Agree

>
>- the check is typed for SMC-R, but the SMC-D path hands a host-order smcd_cdc_msg to
>  smc_cdc_msg_recv() cast as smc_cdc_msg (smc_cdc.c:456), so ntohl/ntohs would
>  double-swap it there. The simplest thing I found is one check on the host cursor
>  right after smc_cdc_msg_to_host(), before the diff/atomic_add block -- that covers
>  SMC-R and SMC-D in one place.

Agree

>
>Minor: >= len rather than > len (count is an offset in [0,len)), and peer_rmbe_size
>is signed so worth guarding. The cons vs peer_rmbe_size bound looks right to me.

No problem

Best regards,
Dust