[syzbot] [net?] WARNING in skb_warn_bad_offload (5)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 80ab5445da62 Merge tag 'wireless-next-2024-07-11' of git:/..
git tree: net-next
console+strace: https://syzkaller.appspot.com/x/log.txt?x=175fb821980000
kernel config: https://syzkaller.appspot.com/x/.config?x=2dbcdd8641c4638f
dashboard link: https://syzkaller.appspot.com/bug?extid=e15b7e15b8a751a91d9a
compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=172bf566980000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=12fff535980000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/184da3869c30/disk-80ab5445.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/85bfe9b60f21/vmlinux-80ab5445.xz
kernel image: https://storage.googleapis.com/syzbot-assets/06064623a948/bzImage-80ab5445.xz

The issue was bisected to:

commit 10154dbded6d6a2fecaebdfda206609de0f121a9
Author: Jakub Sitnicki <ja...@cloudflare.com>
Date: Wed Jun 26 17:51:26 2024 +0000

udp: Allow GSO transmit from devices with no checksum offload

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=142ccbed980000
final oops: https://syzkaller.appspot.com/x/report.txt?x=162ccbed980000
console output: https://syzkaller.appspot.com/x/log.txt?x=122ccbed980000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+e15b7e...@syzkaller.appspotmail.com
Fixes: 10154dbded6d ("udp: Allow GSO transmit from devices with no checksum offload")

skb frag: 00000080: 62 3f 77 e4 0e 82 0d 2f 85 cc 44 ea 25 5a 99 76
skb frag: 00000090: f2 53
------------[ cut here ]------------
ip6tnl0: caps=(0x00000006401d7869, 0x00000006401d7869)
WARNING: CPU: 0 PID: 5112 at net/core/dev.c:3293 skb_warn_bad_offload+0x166/0x1a0 net/core/dev.c:3291
Modules linked in:
CPU: 0 PID: 5112 Comm: syz-executor391 Not tainted 6.10.0-rc7-syzkaller-01603-g80ab5445da62 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/07/2024
RIP: 0010:skb_warn_bad_offload+0x166/0x1a0 net/core/dev.c:3291
Code: e8 5f 94 a3 f8 49 8b 04 24 48 8d 88 a0 03 00 00 48 85 c0 48 0f 44 cd 48 c7 c7 00 cc c5 8c 4c 89 f6 48 89 da e8 fb 92 ff f7 90 <0f> 0b 90 90 5b 41 5c 41 5d 41 5e 41 5f 5d c3 cc cc cc cc 44 89 f9
RSP: 0018:ffffc900034bedc8 EFLAGS: 00010246
RAX: 7d287cad4185da00 RBX: ffff888040cdc0b8 RCX: ffff888023d1bc00
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: ffffffff8cc5cbc0 R08: ffffffff815857b2 R09: fffffbfff1c39994
R10: dffffc0000000000 R11: fffffbfff1c39994 R12: ffff888022880518
R13: dffffc0000000000 R14: ffff888040cdc130 R15: ffff888040cdc130
FS: 000055556e9e9380(0000) GS:ffff8880b9400000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000020001180 CR3: 000000007c876000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<TASK>
__skb_gso_segment+0x3be/0x4c0 net/core/gso.c:127
skb_gso_segment include/net/gso.h:83 [inline]
validate_xmit_skb+0x585/0x1120 net/core/dev.c:3661
__dev_queue_xmit+0x17a4/0x3e90 net/core/dev.c:4415
neigh_output include/net/neighbour.h:542 [inline]
ip6_finish_output2+0xffa/0x1680 net/ipv6/ip6_output.c:137
ip6_finish_output+0x41e/0x810 net/ipv6/ip6_output.c:222
ip6_send_skb+0x112/0x230 net/ipv6/ip6_output.c:1958
udp_v6_send_skb+0xbf5/0x1870 net/ipv6/udp.c:1292
udpv6_sendmsg+0x23b3/0x3270 net/ipv6/udp.c:1588
sock_sendmsg_nosec net/socket.c:730 [inline]
__sock_sendmsg+0xef/0x270 net/socket.c:745
____sys_sendmsg+0x525/0x7d0 net/socket.c:2585
___sys_sendmsg net/socket.c:2639 [inline]
__sys_sendmmsg+0x3b2/0x740 net/socket.c:2725
__do_sys_sendmmsg net/socket.c:2754 [inline]
__se_sys_sendmmsg net/socket.c:2751 [inline]
__x64_sys_sendmmsg+0xa0/0xb0 net/socket.c:2751
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f04f688fe89
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 01 1a 00 00 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffeebc526e8 EFLAGS: 00000246 ORIG_RAX: 0000000000000133
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00007f04f688fe89
RDX: 0000000000000001 RSI: 0000000020003cc0 RDI: 0000000000000003
RBP: 00000000000f4240 R08: 0000000000000000 R09: 0000000000000001
R10: 0000000000000000 R11: 0000000000000246 R12: 00007ffeebc52740
R13: 00007f04f68dd406 R14: 0000000000000003 R15: 00007ffeebc52720
</TASK>


---
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[Paolo Abeni]

Looking at the console log, the the relevant GSO packet is an UFO one
with CSUM_NONE. commit 10154dbded6d6a2fecaebdfda206609de0f121a9 only
adjust the skb csum for USO packets. @Jakub S. could you please have a look?

Thanks!

Paolo

[Jakub Sitnicki]

Will do. Thanks for the hint.

[Eric Dumazet]

The trigger for the bug is the following :

setsockopt(3, SOL_IPV6, IPV6_HOPOPTS,
"\0\3\0\0\0\0\0\0\5\2\0\0\0\1\0\302\4\200\0\0\0\5\2\0\6\302\4\0\0\0\1\302"...,
40) = 0

Some random IPV6_HOPTS, with multiple IPV6_TLV_JUMBO options

Non GSO path sends a malformed packet just fine, but GSO complains loudly.

(flowlabel 0x754ca, hlim 64, next-header Options (0) payload length:
186) localhost > localhost: HBH
(pad1)(pad1)(pad1)(pad1)(pad1)(pad1)(rtalert: 0x0000)
(pad1)(padn)(jumbo: 2147483648 - payload len != 0) (rtalert: 0x0006)
(jumbo: 1 - already seen) [|hbhopt]

[Jakub Sitnicki]

Thank you for the hint. Extracted a reproducer. Fix will follow.

--8<--

~ # cat repro.sh
#!/usr/bin/env bash

unshare -Urn bash <<EOF

set -e

ip link add name sink mtu 1500 type dummy
ip addr add dev sink fd11::1/48 nodad
ip link set dev sink up
ethtool -K sink tx-checksum-ip-generic off >/dev/null
ethtool -K sink tx-udp-segmentation off >/dev/null

ip -6 tunnel add ip6tnl mode ip6ip6 local fd11::1 remote fd11::2
ip link set dev ip6tnl up
ip addr add fd00::1/48 dev ip6tnl

python -c '''

from socket import *

UDP_SEGMENT = 103

hopopts = b"\x00\x03\x00\x00\x00\x00\x00\x00\x05\x02\x00\x00\x00\x01\x00\xc2\x04\x80\x00\x00\x00\x05\x02\x00\x06\xc2\x04\x00\x00\x00\x01\xc2\x04\x00\x00\x00\x04\x00\x00\x00"
s = socket(AF_INET6, SOCK_DGRAM)
s.setsockopt(IPPROTO_IPV6, IPV6_HOPOPTS, hopopts)
s.setsockopt(SOL_UDP, UDP_SEGMENT, 145)
s.sendto(b"x" * 3000, ("fd00::2", 9))

'''

false

EOF
~ # ./repro.sh
[ 59.122084] skb len=3080 headroom=120 headlen=80 tailroom=0
[ 59.122084] mac=(120,0) mac_len=0 net=(120,72) trans=192
[ 59.122084] shinfo(txflags=0 nr_frags=1 gso(size=145 type=131072 segs=21))
[ 59.122084] csum(0x600c0 start=192 offset=6 ip_summed=0 complete_sw=0 valid=0 level=0)
[ 59.122084] hash(0xfd64b255 sw=1 l4=1) proto=0x86dd pkttype=0 iif=0
[ 59.122084] priority=0x0 mark=0x0 alloc_cpu=13 vlan_all=0x0
[ 59.122084] encapsulation=0 inner(proto=0x0000, mac=0, net=0, trans=0)
[ 59.122331] dev name=ip6tnl feat=0x00000006401d5869
[ 59.122362] sk family=10 type=2 proto=17
[ 59.122386] skb linear: 00000000: 60 0d 55 b2 0b e0 00 40 fd 00 00 00 00 00 00 00
[ 59.122428] skb linear: 00000010: 00 00 00 00 00 00 00 01 fd 00 00 00 00 00 00 00
[ 59.122473] skb linear: 00000020: 00 00 00 00 00 00 00 02 11 03 00 00 00 00 00 00
[ 59.122515] skb linear: 00000030: 05 02 00 00 00 01 00 c2 04 80 00 00 00 05 02 00
[ 59.122557] skb linear: 00000040: 06 c2 04 00 00 00 01 c2 ed fb 00 09 0b c0 05 d6
[ 59.122601] skb frag: 00000000: 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78
[ 59.122653] skb frag: 00000010: 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78
[ 59.122696] skb frag: 00000020: 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78
[ 59.122739] skb frag: 00000030: 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78
[ 59.122781] skb frag: 00000040: 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78
[ 59.122824] skb frag: 00000050: 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78
[ 59.122866] skb frag: 00000060: 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78
[ 59.122914] skb frag: 00000070: 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78
[ 59.122957] ------------[ cut here ]------------
[ 59.122987] ip6tnl: caps=(0x00000006401d5869, 0x0000000000000000)
[ 59.123041] WARNING: CPU: 13 PID: 294 at net/core/dev.c:3291 skb_warn_bad_offload+0x86/0xd0
[ 59.123089] Modules linked in:
[ 59.123113] CPU: 13 PID: 294 Comm: python Not tainted 6.10.0-rc7+ #44
[ 59.123149] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
[ 59.123197] RIP: 0010:skb_warn_bad_offload+0x86/0xd0
[ 59.123228] Code: e6 48 c7 c7 79 1b f4 bc 48 85 d2 48 8d 8a a0 03 00 00 48 8d 95 b8 00 00 00 48 0f 44 c8 48 85 ed 48 0f 44 d0 e8 fb 33 4b ff 90 <0f> 0b 90 90 5b 5d 41 5c c3 cc cc cc cc 80 bd 30 01 00 00 00 49 c7
[ 59.123322] RSP: 0018:ffffb25540993990 EFLAGS: 00010282
[ 59.123352] RAX: 0000000000000000 RBX: ffff9262027e6f00 RCX: 0000000000000000
[ 59.123395] RDX: 0000000000000000 RSI: ffffb25540993850 RDI: 0000000000000001
[ 59.123438] RBP: ffff926205ece000 R08: 00000000ffffdfff R09: 0000000000000001
[ 59.123486] R10: 00000000ffffdfff R11: ffffffffbd6a8420 R12: ffff926205ece130
[ 59.123529] R13: 000000000003078c R14: ffff9262027e6f00 R15: 0000000000000050
[ 59.123573] FS: 00007f5188eb1040(0000) GS:ffff92623eb40000(0000) knlGS:0000000000000000
[ 59.123620] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 59.123655] CR2: 0000000000661700 CR3: 00000000027aa000 CR4: 0000000000750ef0
[ 59.123699] PKRU: 55555554
[ 59.123715] Call Trace:
[ 59.123733] <TASK>
[ 59.123751] ? __warn+0x8c/0x190
[ 59.123777] ? skb_warn_bad_offload+0x86/0xd0
[ 59.123808] ? report_bug+0x164/0x190
[ 59.123834] ? handle_bug+0x3b/0x70
[ 59.123860] ? exc_invalid_op+0x17/0x70
[ 59.123884] ? asm_exc_invalid_op+0x1a/0x20
[ 59.123920] ? skb_warn_bad_offload+0x86/0xd0
[ 59.123954] __skb_gso_segment+0xf0/0x170
[ 59.123981] validate_xmit_skb.isra.0+0x15e/0x2c0
[ 59.124011] __dev_queue_xmit+0x217/0x12e0
[ 59.124037] ? lock_acquire+0xc0/0x2d0
[ 59.124063] ? find_held_lock+0x2b/0x80
[ 59.124087] ? ip6_finish_output2+0x27a/0xb20
[ 59.124120] ? lock_release+0xbf/0x290
[ 59.124144] ? lockdep_hardirqs_on_prepare+0xda/0x1a0
[ 59.124175] ip6_finish_output2+0x27a/0xb20
[ 59.124201] ? ip6_mtu+0x9a/0x1c0
[ 59.124225] ? lock_release+0xbf/0x290
[ 59.124251] ip6_finish_output+0x27a/0x4d0
[ 59.124278] ip6_send_skb+0x36/0xb0
[ 59.124304] udp_v6_send_skb+0x1d6/0x480
[ 59.124331] udpv6_sendmsg+0xc04/0xf20
[ 59.124356] ? __lock_acquire+0xe9d/0x16d0
[ 59.124381] ? __pfx_ip_generic_getfrag+0x10/0x10
[ 59.124415] ? release_sock+0x1d/0xb0
[ 59.124441] ? find_held_lock+0x2b/0x80
[ 59.124464] ? find_held_lock+0x2b/0x80
[ 59.124491] ? __sys_sendto+0x123/0x1f0
[ 59.124516] __sys_sendto+0x123/0x1f0
[ 59.124544] ? __rseq_handle_notify_resume+0x42a/0x5c0
[ 59.124579] __x64_sys_sendto+0x24/0x30
[ 59.124603] do_syscall_64+0xbb/0x1d0
[ 59.124628] entry_SYSCALL_64_after_hwframe+0x77/0x7f
[ 59.124660] RIP: 0033:0x7f5188fdca37
[ 59.124684] Code: 0d 00 f7 d8 64 89 02 48 c7 c0 ff ff ff ff eb b8 0f 1f 00 f3 0f 1e fa 80 3d 15 bb 0d 00 00 41 89 ca 74 10 b8 2c 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 71 c3 55 48 83 ec 30 44 89 4c 24 2c 4c 89 44
[ 59.124775] RSP: 002b:00007ffe9b877698 EFLAGS: 00000202 ORIG_RAX: 000000000000002c
[ 59.124817] RAX: ffffffffffffffda RBX: 00007ffe9b877738 RCX: 00007f5188fdca37
[ 59.124860] RDX: 0000000000000bb8 RSI: 000000003998f950 RDI: 0000000000000003
[ 59.124903] RBP: 0000000000000000 R08: 00007ffe9b8777b0 R09: 000000000000001c
[ 59.124947] R10: 0000000000000000 R11: 0000000000000202 R12: 0000000000000000
[ 59.124990] R13: 0000000000000000 R14: 00000000004a86e2 R15: 0000000000a71a18
[ 59.125037] </TASK>
[ 59.125055] irq event stamp: 54030
[ 59.125078] hardirqs last enabled at (54040): [<ffffffffbb9e10fd>] console_unlock+0x10d/0x130
[ 59.125127] hardirqs last disabled at (54049): [<ffffffffbb9e10e2>] console_unlock+0xf2/0x130
[ 59.125176] softirqs last enabled at (53220): [<ffffffffbc4a9de9>] ___neigh_create+0x959/0xe30
[ 59.125224] softirqs last disabled at (53224): [<ffffffffbc494736>] __dev_queue_xmit+0x76/0x12e0
[ 59.125273] ---[ end trace 0000000000000000 ]---
~ #

[Jakub Sitnicki]

Thanks for the patience.

I've got a fix to propose which pulls the gso_skb->ip_summed tweak added
to __udp_gso_segment() in commit 10154dbded6d ("udp: Allow GSO transmit
from devices with no checksum offload") from gso/udp code up to the udp
layer (udp[_v6]_send_skb()).

This warning can also be triggered for an ipv4 tunnel by turning off
csum offload (ethtool -K $tnl tx-checksum-ip-generic off). Will extend
udpgso.sh test to cover both v4 and v6.

[...]

[Jakub Sitnicki]

Proposed fix now posted:

https://lore.kernel.org/all/20240725-udp-gso-egress-fr...@cloudflare.com/