Re: [syzbot] [net?] KASAN: use-after-free Read in __skb_flow_dissect (3)

From: Hillf Danton
Date: Wed Jan 17 2024 - 17:52:14 EST


On Mon, 01 Jan 2024 09:18:16 -0800
> syzbot found the following issue on:
>
> HEAD commit: f5837722ffec Merge tag 'mm-hotfixes-stable-2023-12-27-15-0..
> git tree: upstream
> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=122dfc65e80000

#syz test https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master

--- x/net/core/flow_dissector.c
+++ y/net/core/flow_dissector.c
@@ -1164,9 +1164,11 @@ proto_again:
switch (proto) {
case htons(ETH_P_IP): {
const struct iphdr *iph;
- struct iphdr _iph;

- iph = __skb_header_pointer(skb, nhoff, sizeof(_iph), data, hlen, &_iph);
+ if (pskb_network_may_pull(skb, sizeof(struct iphdr)))
+ iph = (void *) skb_network_header(skb);
+ else
+ iph = NULL;
if (!iph || iph->ihl < 5) {
fdret = FLOW_DISSECT_RET_OUT_BAD;
break;
--