wifi: brcmfmac: Fix oops due to NULL pointer dereference in brcmf_sdiod_sglist_rw()

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: wifi: brcmfmac: Fix oops due to NULL pointer dereference in brcmf_sdiod_sglist_rw() 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. 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.

References

• https://git.kernel.org/stable/c/342f87d263462c2670b77ea9a32074cab2ac6fa1
• https://git.kernel.org/stable/c/7522d7d745d13fbeff3350fe6aa56c8dae263571
• https://git.kernel.org/stable/c/dfb3f9d3f602602de208da7bdcc0f6d5ee74af68
• https://git.kernel.org/stable/c/67a25ea28f8ec1da8894f2f115d01d3becf67dc7
• https://git.kernel.org/stable/c/07c020c6d14d29e5a3ea4e4576b8ecf956a80834
• https://git.kernel.org/stable/c/34941321b516bd7c6103bd01287d71a1804d19d3
• https://git.kernel.org/stable/c/857282b819cbaa0675aaab1e7542e2c0579f52d7