Re: [PATCH] wifi: brcmfmac: Fix oops due to NULL pointer dereference in 'brcmf_sdiod_sglist_rw'

[Kalle Valo <kvalo@kernel.org>]

Arend van Spriel <arend.vanspriel@broadcom.com> writes:

> On 11/7/2024 9:07 AM, Kalle Valo wrote:
>
>> Norbert van Bolhuis <nvbolhuis@gmail.com> writes:
>> 
>>> This patch fixes a NULL pointer dereference bug in brcmfmac that occurs
>>> when a high 'sd_sgentry_align' value applies (e.g. 512) and a lot of queued SKBs
>>> are sent from the pkt queue.
>>>
>>> The problem is the number of entries in the pre-allocated sgtable, it is
>>> nents = max(rxglom_size, txglom_size) + max(rxglom_size, txglom_size) >> 4 + 1.
>>> Given the default [rt]xglom_size=32 it's actually 35 which is too small.
>>> Worst case, the pkt queue can end up with 64 SKBs. This occurs when a new SKB
>>> is added for each original SKB if tailroom isn't enough to hold tail_pad.
>>> At least one sg entry is needed for each SKB. So, eventually the "skb_queue_walk loop"
>>> in brcmf_sdiod_sglist_rw may run out of sg entries. This makes sg_next return
>>> NULL and this causes the oops.
>> BTW it would be good to fix (in a separate patch) the sg handling so
>> that the kernel won't oops when sg entries rung. That's not really
>> robust behaviour.
>> 
>>> The patch sets nents to max(rxglom_size, txglom_size) * 2 to be able handle
>>> the worst-case.
>>> Btw. this requires only 64-35=29 * 16 (or 20 if CONFIG_NEED_SG_DMA_LENGTH) = 464
>>> additional bytes of memory.
>> s-o-b missing, please read our documentation from the link below.
>
> I have not seen the actual patch. Which mailing list was it sent to?

Only to linux-wireless, adding brcm80211 now. But the patch is in
patchwork:

https://patchwork.kernel.org/project/linux-wireless/patch/20241105204011.1603148-1-norbert.vanbolhuis@ev-box.com/

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