Norbert van Bolhuis <nvbolhuis@xxxxxxxxx> 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. -- https://patchwork.kernel.org/project/linux-wireless/list/ https://wireless.wiki.kernel.org/en/developers/documentation/submittingpatches
