Re: v4.14-rc2/arm64 kernel BUG at net/core/skbuff.c:2626

On Mon, Oct 2, 2017 at 10:21 AM, Mark Rutland [off-list ref] wrote:

On Mon, Oct 02, 2017 at 07:48:28AM -0700, Eric Dumazet wrote:

quoted

Please try the following fool proof patch.

This is what I had in my local tree back in August but could not
conclude on the syzkaller bug I was working on.

diff --git a/net/ipv4/icmp.c b/net/ipv4/icmp.c
index 681e33998e03b609fdca83a83e0fc62a3fee8c39..e51d777797a927058760a1ab7af00579f7488cb5 100644
--- a/net/ipv4/icmp.c
+++ b/net/ipv4/icmp.c

@@ -732,7 +732,8 @@ void icmp_send(struct sk_buff *skb_in, int type, int code, __be32 info)
              room = 576;
      room -= sizeof(struct iphdr) + icmp_param.replyopts.opt.opt.optlen;
      room -= sizeof(struct icmphdr);
-
+     if (room < 0)
+             goto ende;
      icmp_param.data_len = skb_in->len - icmp_param.offset;
      if (icmp_param.data_len > room)
              icmp_param.data_len = room;

Unfortuantely, with this applied I still see the issue.

Syzkaller came up with a minimized reproducer [1], which can trigger the
issue near instantly under syz-execprog. If there's anything that would
help to narrow this down, I'm more than happy to give it a go.

Thanks,
Mark.

[1] https://www.kernel.org/pub/linux/kernel/people/mark/bugs/20171002-skb_clone-misaligned-atomic/syzkaller.repro

Note that I was not trying to address the misaligned stuff.

Only this :

------------[ cut here ]------------
kernel BUG at net/core/skbuff.c:2626!
Internal error: Oops - BUG: 0 [#1] PREEMPT SMP
Modules linked in:
CPU: 3 PID: 0 Comm: swapper/3 Not tainted 4.14.0-rc2-00001-gd7ad33d #115
Hardware name: linux,dummy-virt (DT)
task: ffff80003a901a80 task.stack: ffff80003a908000
PC is at skb_copy_and_csum_bits+0x8dc/0xae0 net/core/skbuff.c:2626
LR is at skb_copy_and_csum_bits+0x8dc/0xae0 net/core/skbuff.c:2626