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

[Hillf Danton]

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/filter.c
+++ y/net/core/filter.c
@@ -2161,6 +2161,10 @@ static int __bpf_redirect_no_mac(struct
 	}
 	skb_pop_mac_header(skb);
 	skb_reset_mac_len(skb);
+
+	if (skb->data[0] < 2)
+		flags = 0;
+
 	return flags & BPF_F_INGRESS ?
 	       __bpf_rx_skb_no_mac(dev, skb) : __bpf_tx_skb(dev, skb);
 }
--