Re: [syzbot] [atm?] general protection fault in atmtcp_c_send

[Hillf Danton]

> Date: Wed, 20 Aug 2025 18:29:32 -0700	[thread overview]
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    bab3ce404553 Merge branch '100GbE' of git://git.kernel.org..
> git tree:       net-next
> console+strace: https://syzkaller.appspot.com/x/log.txt?x=164893a2580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=412ee2f8b704a5e6
> dashboard link: https://syzkaller.appspot.com/bug?extid=1741b56d54536f4ec349
> compiler:       Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1769faf0580000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=100eaba2580000

#syz test

--- x/drivers/atm/atmtcp.c
+++ y/drivers/atm/atmtcp.c
@@ -294,6 +294,8 @@ static int atmtcp_c_send(struct atm_vcc
 	dev = vcc->dev_data;
 	hdr = (struct atmtcp_hdr *) skb->data;
 	if (hdr->length == ATMTCP_HDR_MAGIC) {
+		if (skb->len < sizeof(struct atmtcp_control))
+			goto done;
 		result = atmtcp_recv_control(
 		    (struct atmtcp_control *) skb->data);
 		goto done;
--