Re: [PATCH net] ipv4: ip_gre: Handle skb_pull() failure in ipgre_xmit()

[Eric Dumazet]

On Tue, Nov 28, 2023 at 4:51 PM Paolo Abeni <pabeni@xxxxxxxxxx> wrote:
>
> On Tue, 2023-11-28 at 16:45 +0100, Eric Dumazet wrote:
> > On Sun, Nov 26, 2023 at 4:17 PM Shigeru Yoshida <syoshida@xxxxxxxxxx> wrote:
> > >
> > > In ipgre_xmit(), skb_pull() may fail even if pskb_inet_may_pull() returns
> > > true. For example, applications can create a malformed packet that causes
> > > this problem with PF_PACKET.
> > >
> > > This patch fixes the problem by dropping skb and returning from the
> > > function if skb_pull() fails.
> > >
> > > Fixes: c54419321455 ("GRE: Refactor GRE tunneling code.")
> > > Signed-off-by: Shigeru Yoshida <syoshida@xxxxxxxxxx>
> > > ---
> > >  net/ipv4/ip_gre.c | 3 ++-
> > >  1 file changed, 2 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/net/ipv4/ip_gre.c b/net/ipv4/ip_gre.c
> > > index 22a26d1d29a0..95efa97cb84b 100644
> > > --- a/net/ipv4/ip_gre.c
> > > +++ b/net/ipv4/ip_gre.c
> > > @@ -643,7 +643,8 @@ static netdev_tx_t ipgre_xmit(struct sk_buff *skb,
> > >                 /* Pull skb since ip_tunnel_xmit() needs skb->data pointing
> > >                  * to gre header.
> > >                  */
> > > -               skb_pull(skb, tunnel->hlen + sizeof(struct iphdr));
> > > +               if (!skb_pull(skb, tunnel->hlen + sizeof(struct iphdr)))
> > > +                       goto free_skb;
> > >                 skb_reset_mac_header(skb);
> > >
> > >                 if (skb->ip_summed == CHECKSUM_PARTIAL &&
> > > --
> >
> >
> > I have syszbot reports with an actual repro for this one.
>
> Could you please share them? I could not find easily the reports in
> https://syzkaller.appspot.com/upstream

Stack trace looks like the following:

skbuff: skb_under_panic: text:ffffffff845f50a0 len:920 put:20
head:ffff888171931000 data:ffff888171930ff8 tail:0x390 end:0x680
dev:gre4
------------[ cut here ]------------
kernel BUG at net/core/skbuff.c:120 !
invalid opcode: 0000 [#1] PREEMPT SMP KASAN
CPU: 0 PID: 12705 Comm: kworker/0:0 Not tainted
6.1.43-syzkaller-00022-g8f46c3493178 #0
Hardware name: Google Google Compute Engine/Google Compute Engine,
BIOS Google 10/09/2023
Workqueue: mld mld_ifc_work
RIP: 0010:skb_panic net/core/skbuff.c:120 [inline]
RIP: 0010:skb_under_panic+0x14c/0x150 net/core/skbuff.c:130
Code: 60 98 da 85 48 c7 c6 05 6b 2f 86 48 8b 55 c0 8b 4d d4 44 8b 45
d0 4c 8b 4d c8 53 41 55 41 54 41 57 e8 fc db f4 00 48 83 c4 20 <0f> 0b
66 90 55 48 89 e5 41 57 41 56 41 55 41 54 53 48 83 ec 18 41
RSP: 0018:ffffc9000551f0a0 EFLAGS: 00010286
RAX: 0000000000000087 RBX: ffff888162226000 RCX: 98ecdd4da3f28000
RDX: 0000000000000000 RSI: 0000000000000400 RDI: 0000000000000000
RBP: ffffc9000551f0e0 R08: ffffffff815a9ea5 R09: fffff52000aa3dad
R10: 0000000000000000 R11: dffffc0000000001 R12: 0000000000000390
R13: 0000000000000680 R14: dffffc0000000000 R15: ffff888171930ff8
FS: 0000000000000000(0000) GS:ffff8881f7000000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000001b2f421000 CR3: 000000010f5a3000 CR4: 00000000003506b0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<TASK>
skb_push+0xf3/0x120 net/core/skbuff.c:2181
iptunnel_xmit+0x2d0/0x940 net/ipv4/ip_tunnel_core.c:67
ip_tunnel_xmit+0x218f/0x2ae0 net/ipv4/ip_tunnel.c:813
__gre_xmit net/ipv4/ip_gre.c:469 [inline]
ipgre_xmit+0x7ac/0xaa0 net/ipv4/ip_gre.c:661
__netdev_start_xmit include/linux/netdevice.h:4908 [inline]
netdev_start_xmit include/linux/netdevice.h:4922 [inline]
xmit_one net/core/dev.c:3602 [inline]
dev_hard_start_xmit+0x1de/0x630 net/core/dev.c:3618
__dev_queue_xmit+0x18c0/0x3700 net/core/dev.c:4268
dev_queue_xmit include/linux/netdevice.h:3076 [inline]
neigh_direct_output+0x17/0x20 net/core/neighbour.c:1592
neigh_output include/net/neighbour.h:552 [inline]
ip6_finish_output2+0x104a/0x1820 net/ipv6/ip6_output.c:134
__ip6_finish_output net/ipv6/ip6_output.c:195 [inline]
ip6_finish_output+0x5d9/0xb60 net/ipv6/ip6_output.c:206
NF_HOOK_COND include/linux/netfilter.h:294 [inline]
ip6_output+0x1f7/0x4d0 net/ipv6/ip6_output.c:227
dst_output include/net/dst.h:444 [inline]
NF_HOOK include/linux/netfilter.h:305 [inline]
mld_sendpack+0x803/0xe40 net/ipv6/mcast.c:1820
mld_send_cr net/ipv6/mcast.c:2121 [inline]
mld_ifc_work+0x7dc/0xba0 net/ipv6/mcast.c:2653
process_one_work+0x73d/0xcb0 kernel/workqueue.c:2299
worker_thread+0xa60/0x1260 kernel/workqueue.c:2446
kthread+0x26d/0x300 kernel/kthread.c:376
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:306
</TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:skb_panic net/core/skbuff.c:120 [inline]
RIP: 0010:skb_under_panic+0x14c/0x150 net/core/skbuff.c:130
Code: 60 98 da 85 48 c7 c6 05 6b 2f 86 48 8b 55 c0 8b 4d d4 44 8b 45
d0 4c 8b 4d c8 53 41 55 41 54 41 57 e8 fc db f4 00 48 83 c4 20 <0f> 0b
66 90 55 48 89 e5 41 57 41 56 41 55 41 54 53 48 83 ec 18 41
RSP: 0018:ffffc9000551f0a0 EFLAGS: 00010286
RAX: 0000000000000087 RBX: ffff888162226000 RCX: 98ecdd4da3f28000
RDX: 0000000000000000 RSI: 0000000000000400 RDI: 0000000000000000
RBP: ffffc9000551f0e0 R08: ffffffff815a9ea5 R09: fffff52000aa3dad
R10: 0000000000000000 R11: dffffc0000000001 R12: 0000000000000390
R13: 0000000000000680 R14: dffffc0000000000 R15: ffff888171930ff8
FS: 0000000000000000(0000) GS:ffff8881f7000000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000001b2f421000 CR3: 000000010f5a3000 CR4: 00000000003506b0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400