Re: [PATCH net] hinic3: bound the Rx fragment count to MAX_SKB_FRAGS

[Sebastian Andrzej Siewior <bigeasy@linutronix.de>]

On 2026-10-19 09:10:37 [+0900], Yehyeong Lee wrote:
> Thanks for the review.
> 
> A well-behaved device can't reach it. rx_buf_len is fixed at 2048
> regardless of MTU, so the frag count is ceil(pkt_len / 2048): a max-MTU
> frame (9600) is 5 frags, and LRO -- off by default, capped at 32K when
> enabled -- is at most 16, both below the 17 the array holds. Only the
> 16-bit length field in the completion descriptor (RQ_CQE_SGE_LEN_MASK)
> lets a device claim up to 65535 bytes, i.e. 32 frags. So it takes a
> device reporting a bogus length, i.e. broken or malicious firmware,
> which is why I treated it as a robustness fix -- I should have said so
> in the changelog.

If this is something that in general opinion never can be reached then
it might be something to target net-next and not net looking like a fix.

> I found it by code inspection, not in the field, and I don't have a
> hinic3 card, so it's untested on real hardware; I reproduced it by
> injecting an out-of-range length to get the KASAN splat in the
> changelog. The netdev bot asked for these same two things, so this
> answers it as well.

I see. That KASAN splat makes it look like something that was really
reproduced. I assumed jumbo frames and aggregation at HW level.
Just because a field is 16 bit wide, it does not mean the hardware will
utilise all its fields. 

> You're right that the bare drop is unhelpful. It only surfaces as
> rx_dropped via ndo_get_stats64, not in ethtool -S -- hinic3 has no
> get_ethtool_stats, and the stats series in net-next doesn't export
> dropped either. I'm happy to add a net_warn_ratelimited() on the
> discard path in v2; it only fires for a misbehaving device, so it won't
> spam a healthy system. Let me know if you'd like that.

I would suggest to target net-next if this can not be reached and is
just there to address a possible overflow. Maybe a warning if it was
reached after all. Fan has probably an opinion here.

> For reference, eea does the same thing -- it drops once nr_frags
> reaches MAX_SKB_FRAGS.
> 
> Thanks,
> Yehyeong

Sebastian