From: "Jason A. Donenfeld" <Jason@zx2c4.com>
To: Netdev <netdev@vger.kernel.org>
Cc: syzkaller-bugs@googlegroups.com,
WireGuard mailing list <wireguard@lists.zx2c4.com>,
Eric Dumazet <edumazet@google.com>
Subject: Re: UBSAN: object-size-mismatch in wg_xmit
Date: Sun, 20 Dec 2020 22:11:00 +0100 [thread overview]
Message-ID: <CAHmME9qwbB7kbD=1sg_81=82vO07XMV7GyqBcCoC=zwM-v47HQ@mail.gmail.com> (raw)
In-Reply-To: <000000000000e13e2905b6e830bb@google.com>
Hmm, on first glance, I'm not sure I'm seeing the bug:
On Sun, Dec 20, 2020 at 5:54 PM syzbot
<syzbot+8f90d005ab2d22342b6d@syzkaller.appspotmail.com> wrote:
> UBSAN: object-size-mismatch in ./include/linux/skbuff.h:2021:28
> member access within address 0000000085889cc2 with insufficient space
> for an object of type 'struct sk_buff'
> __skb_queue_before include/linux/skbuff.h:2021 [inline]
> __skb_queue_tail include/linux/skbuff.h:2054 [inline]
> wg_xmit+0x45d/0xdf0 drivers/net/wireguard/device.c:182
The code in question is:
struct sk_buff_head packets;
__skb_queue_head_init(&packets);
...
skb_list_walk_safe(skb, skb, next) {
skb_mark_not_on_list(skb);
skb = skb_share_check(skb, GFP_ATOMIC);
if (unlikely(!skb))
continue;
...
__skb_queue_tail(&packets, skb);
}
We're in a netdev's xmit function, so nothing else should have skb at
that point. Given the warning is about "member access", I assume it's
the next->prev dereference here:
static inline void __skb_queue_before(struct sk_buff_head *list,
struct sk_buff *next,
struct sk_buff *newsk)
{
__skb_insert(newsk, next->prev, next, list);
}
So where is "next" coming from that UBSAN would complain about
object-size-mismatch?
static inline void __skb_queue_tail(struct sk_buff_head *list,
struct sk_buff *newsk)
{
__skb_queue_before(list, (struct sk_buff *)list, newsk);
}
It comes from casting "list" into an sk_buff. While this might be some
CFI-violating polymorphism, I can't see why this cast would actually
be a problem in practice. The top of sk_buff is intentionally the same
as sk_buff_head:
struct sk_buff_head {
struct sk_buff *next;
struct sk_buff *prev;
...
struct sk_buff {
union {
struct {
struct sk_buff *next;
struct sk_buff *prev;
...
I'd suspect, "oh maybe it's just a clang 11 bug", but syzbot says it
can't reproduce. So that makes me a little more nervous.
Does anybody see something I've missed?
Jason
next prev parent reply other threads:[~2020-12-20 21:11 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-20 16:54 syzbot
2020-12-20 21:11 ` Jason A. Donenfeld [this message]
2020-12-21 9:14 ` Dmitry Vyukov
2020-12-21 11:23 ` Jason A. Donenfeld
2021-01-07 12:22 ` Dmitry Vyukov
2021-01-07 19:00 ` Jason A. Donenfeld
2021-01-07 19:06 ` Jeffrey Walton
2021-01-08 0:34 ` Corey Costello
2021-01-08 0:42 ` Eric Light
2021-01-08 0:44 ` Corey Costello
2021-01-08 0:50 ` Eric Light
2021-01-08 1:02 ` Phillip McMahon
2021-01-08 9:33 ` Dmitry Vyukov
2021-01-08 20:54 ` Nathan Chancellor
2021-01-08 9:30 ` Dmitry Vyukov
[not found] ` <CAGXu5j+jzmkiU_AWoTVF6e263iYSSJYUHB=Kdqh-MCfEO-aNSg@mail.gmail.com>
2021-01-09 9:46 ` Dmitry Vyukov
2021-01-09 10:49 ` Matthias Urlichs
2021-01-11 17:17 ` Dmitry Vyukov
2021-01-11 17:35 ` Jeffrey Walton
2021-01-11 17:58 ` Dmitry Vyukov
2021-01-11 18:14 ` Jeffrey Walton
2021-01-12 9:54 ` Dmitry Vyukov
2021-01-07 12:53 ` Jeffrey Walton
2021-01-07 17:01 ` Julian Wiedmann
2021-01-07 18:58 ` Jason A. Donenfeld
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