KMSAN: uninit-value in __netif_receive_skb_core

[syzbot]

Hello,

syzbot hit the following crash on
https://github.com/google/kmsan.git/master commit
e2ab7e8abba47a2f2698216258e5d8727ae58717 (Fri Apr 6 16:24:31 2018 +0000)
kmsan: temporarily disable visitAsmInstruction() to help syzbot
syzbot dashboard link:
https://syzkaller.appspot.com/bug?extid=b202b7208664142954fa

Unfortunately, I don't have any reproducer for this crash yet.
Raw console output:
https://syzkaller.appspot.com/x/log.txt?id=5356516437655552
Kernel config:
https://syzkaller.appspot.com/x/.config?id=6627248707860932248
compiler: clang version 7.0.0 (trunk 329391)

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+b202b7...@syzkaller.appspotmail.com
It will help syzbot understand when the bug is fixed. See footer for
details.
If you forward the report, please keep this part and the footer.

==================================================================
BUG: KMSAN: uninit-value in __read_once_size include/linux/compiler.h:197
[inline]
BUG: KMSAN: uninit-value in deliver_ptype_list_skb net/core/dev.c:1908
[inline]
BUG: KMSAN: uninit-value in __netif_receive_skb_core+0x4630/0x4a80
net/core/dev.c:4545
CPU: 0 PID: 5999 Comm: syz-executor3 Not tainted 4.16.0+ #82
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
Call Trace:
<IRQ>
__dump_stack lib/dump_stack.c:17 [inline]
dump_stack+0x185/0x1d0 lib/dump_stack.c:53
kmsan_report+0x142/0x240 mm/kmsan/kmsan.c:1067
__msan_warning_32+0x6c/0xb0 mm/kmsan/kmsan_instr.c:676
__read_once_size include/linux/compiler.h:197 [inline]
deliver_ptype_list_skb net/core/dev.c:1908 [inline]
__netif_receive_skb_core+0x4630/0x4a80 net/core/dev.c:4545
__netif_receive_skb net/core/dev.c:4627 [inline]
process_backlog+0x62d/0xe20 net/core/dev.c:5307
napi_poll net/core/dev.c:5705 [inline]
net_rx_action+0x7c1/0x1a70 net/core/dev.c:5771
__do_softirq+0x56d/0x93d kernel/softirq.c:285
do_softirq_own_stack+0x2a/0x40 arch/x86/entry/entry_64.S:1040
</IRQ>
do_softirq kernel/softirq.c:329 [inline]
__local_bh_enable_ip+0x114/0x140 kernel/softirq.c:182
local_bh_enable+0x36/0x40 include/linux/bottom_half.h:32
rcu_read_unlock_bh include/linux/rcupdate.h:726 [inline]
__dev_queue_xmit+0x2a31/0x2b60 net/core/dev.c:3584
dev_queue_xmit+0x4b/0x60 net/core/dev.c:3590
packet_snd net/packet/af_packet.c:2944 [inline]
packet_sendmsg+0x7c57/0x8a10 net/packet/af_packet.c:2969
sock_sendmsg_nosec net/socket.c:630 [inline]
sock_sendmsg net/socket.c:640 [inline]
sock_write_iter+0x3b9/0x470 net/socket.c:909
do_iter_readv_writev+0x7bb/0x970 include/linux/fs.h:1776
do_iter_write+0x30d/0xd40 fs/read_write.c:932
vfs_writev fs/read_write.c:977 [inline]
do_writev+0x3c9/0x830 fs/read_write.c:1012
SYSC_writev+0x9b/0xb0 fs/read_write.c:1085
SyS_writev+0x56/0x80 fs/read_write.c:1082
do_syscall_64+0x309/0x430 arch/x86/entry/common.c:287
entry_SYSCALL_64_after_hwframe+0x3d/0xa2
RIP: 0033:0x455259
RSP: 002b:00007fb53ede8c68 EFLAGS: 00000246 ORIG_RAX: 0000000000000014
RAX: ffffffffffffffda RBX: 00007fb53ede96d4 RCX: 0000000000455259
RDX: 0000000000000001 RSI: 00000000200010c0 RDI: 0000000000000013
RBP: 000000000072bea0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
R13: 00000000000006cd R14: 00000000006fd3d8 R15: 0000000000000000

Uninit was stored to memory at:
kmsan_save_stack_with_flags mm/kmsan/kmsan.c:278 [inline]
kmsan_save_stack mm/kmsan/kmsan.c:293 [inline]
kmsan_internal_chain_origin+0x12b/0x210 mm/kmsan/kmsan.c:684
__msan_chain_origin+0x69/0xc0 mm/kmsan/kmsan_instr.c:521
skb_vlan_untag+0x950/0xee0 include/linux/if_vlan.h:597
__netif_receive_skb_core+0x70a/0x4a80 net/core/dev.c:4460
__netif_receive_skb net/core/dev.c:4627 [inline]
process_backlog+0x62d/0xe20 net/core/dev.c:5307
napi_poll net/core/dev.c:5705 [inline]
net_rx_action+0x7c1/0x1a70 net/core/dev.c:5771
__do_softirq+0x56d/0x93d kernel/softirq.c:285
Uninit was created at:
kmsan_save_stack_with_flags mm/kmsan/kmsan.c:278 [inline]
kmsan_internal_poison_shadow+0xb8/0x1b0 mm/kmsan/kmsan.c:188
kmsan_kmalloc+0x94/0x100 mm/kmsan/kmsan.c:314
kmsan_slab_alloc+0x11/0x20 mm/kmsan/kmsan.c:321
slab_post_alloc_hook mm/slab.h:445 [inline]
slab_alloc_node mm/slub.c:2737 [inline]
__kmalloc_node_track_caller+0xaed/0x11c0 mm/slub.c:4369
__kmalloc_reserve net/core/skbuff.c:138 [inline]
__alloc_skb+0x2cf/0x9f0 net/core/skbuff.c:206
alloc_skb include/linux/skbuff.h:984 [inline]
alloc_skb_with_frags+0x1d4/0xb20 net/core/skbuff.c:5234
sock_alloc_send_pskb+0xb56/0x1190 net/core/sock.c:2085
packet_alloc_skb net/packet/af_packet.c:2803 [inline]
packet_snd net/packet/af_packet.c:2894 [inline]
packet_sendmsg+0x6444/0x8a10 net/packet/af_packet.c:2969
sock_sendmsg_nosec net/socket.c:630 [inline]
sock_sendmsg net/socket.c:640 [inline]
sock_write_iter+0x3b9/0x470 net/socket.c:909
do_iter_readv_writev+0x7bb/0x970 include/linux/fs.h:1776
do_iter_write+0x30d/0xd40 fs/read_write.c:932
vfs_writev fs/read_write.c:977 [inline]
do_writev+0x3c9/0x830 fs/read_write.c:1012
SYSC_writev+0x9b/0xb0 fs/read_write.c:1085
SyS_writev+0x56/0x80 fs/read_write.c:1082
do_syscall_64+0x309/0x430 arch/x86/entry/common.c:287
entry_SYSCALL_64_after_hwframe+0x3d/0xa2
==================================================================


---
This bug is generated by a dumb bot. It may contain errors.
See https://goo.gl/tpsmEJ for details.
Direct all questions to syzk...@googlegroups.com.

syzbot will keep track of this bug report.
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[Dmitry Vyukov]

On Thu, Apr 12, 2018 at 10:01 AM, syzbot
<syzbot+b202b7...@syzkaller.appspotmail.com> wrote:
> Hello,
>
> syzbot hit the following crash on https://github.com/google/kmsan.git/master
> commit
> e2ab7e8abba47a2f2698216258e5d8727ae58717 (Fri Apr 6 16:24:31 2018 +0000)
> kmsan: temporarily disable visitAsmInstruction() to help syzbot
> syzbot dashboard link:
> https://syzkaller.appspot.com/bug?extid=b202b7208664142954fa
>
> Unfortunately, I don't have any reproducer for this crash yet.
> Raw console output:
> https://syzkaller.appspot.com/x/log.txt?id=5356516437655552
> Kernel config:
> https://syzkaller.appspot.com/x/.config?id=6627248707860932248
> compiler: clang version 7.0.0 (trunk 329391)

+Toshiaki as this seems to be related to the recent vlan tagging changes.
This also seems to be related to
https://groups.google.com/d/msg/syzkaller-bugs/VRH9NnUi2k0/90GYsAeRBgAJ

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[syzbot]

syzbot has found reproducer for the following crash on
https://github.com/google/kmsan.git/master commit
35ff515e4bda2646f6c881d33951c306ea9c282a (Tue Apr 10 08:59:43 2018 +0000)
Merge pull request #11 from parkerduckworth/readme

syzbot dashboard link:
https://syzkaller.appspot.com/bug?extid=b202b7208664142954fa

So far this crash happened 3 times on
https://github.com/google/kmsan.git/master.
C reproducer: https://syzkaller.appspot.com/x/repro.c?id=4559916236800000
syzkaller reproducer:
https://syzkaller.appspot.com/x/repro.syz?id=4590273065648128
Raw console output:
https://syzkaller.appspot.com/x/log.txt?id=4631921027973120

Kernel config:
https://syzkaller.appspot.com/x/.config?id=6627248707860932248
compiler: clang version 7.0.0 (trunk 329391)

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+b202b7...@syzkaller.appspotmail.com
It will help syzbot understand when the bug is fixed.

==================================================================
BUG: KMSAN: uninit-value in __read_once_size include/linux/compiler.h:197
[inline]
BUG: KMSAN: uninit-value in deliver_ptype_list_skb net/core/dev.c:1908
[inline]
BUG: KMSAN: uninit-value in __netif_receive_skb_core+0x4630/0x4a80
net/core/dev.c:4545

CPU: 0 PID: 3514 Comm: syzkaller031167 Not tainted 4.16.0+ #83

RIP: 0033:0x43ffb9
RSP: 002b:00007ffd42187708 EFLAGS: 00000217 ORIG_RAX: 0000000000000014
RAX: ffffffffffffffda RBX: 00000000004002c8 RCX: 000000000043ffb9
RDX: 0000000000000001 RSI: 00000000200010c0 RDI: 0000000000000003
RBP: 00000000006ca018 R08: 00000000004002c8 R09: 00000000004002c8
R10: 00000000004002c8 R11: 0000000000000217 R12: 00000000004018e0
R13: 0000000000401970 R14: 0000000000000000 R15: 0000000000000000

[Toshiaki Makita]

On 2018/04/12 17:03, Dmitry Vyukov wrote:
> On Thu, Apr 12, 2018 at 10:01 AM, syzbot
> <syzbot+b202b7...@syzkaller.appspotmail.com> wrote:
>> Hello,
>>
>> syzbot hit the following crash on https://github.com/google/kmsan.git/master
>> commit
>> e2ab7e8abba47a2f2698216258e5d8727ae58717 (Fri Apr 6 16:24:31 2018 +0000)
>> kmsan: temporarily disable visitAsmInstruction() to help syzbot
>> syzbot dashboard link:
>> https://syzkaller.appspot.com/bug?extid=b202b7208664142954fa
>>
>> Unfortunately, I don't have any reproducer for this crash yet.
>> Raw console output:
>> https://syzkaller.appspot.com/x/log.txt?id=5356516437655552
>> Kernel config:
>> https://syzkaller.appspot.com/x/.config?id=6627248707860932248
>> compiler: clang version 7.0.0 (trunk 329391)
>
> +Toshiaki as this seems to be related to the recent vlan tagging changes.

seems not...
"Uninit was stored to memory at:" shows uninitialized memory was stored
before where I modified the code (skb_reorder_vlan_header).

I'm not sure what this uninit memory means.
To me it looks like the memory is initialized by user provided data.

(iov in packet sock -> skb->data -> skb->protocol)

The reproducer provides 4 bytes after ethernet header, so it should be
sufficient for a vlan tag. This will set skb->len to 4 and fill the
4-byte contents in packet_snd(). skb_vlan_untag() is reading the user
provided 4-byte skb->data. It is ensured that skb_vlan_untag() does not
read beyond skb->len since it calls pskb_may_pull(). At this point I am
failing to find what I am missing.

--
Toshiaki Makita

[Dmitry Vyukov]

Eric,

You mentioned something about assumption that the
__vlan_insert_inner_tag() helper would only be called from
__netif_receive_skb_core(). Can you elaborate?

[syzbot]

syzbot has bisected this issue to:

commit e420bed025071a623d2720a92bc2245c84757ecb
Author: Daniel Borkmann <dan...@iogearbox.net>
Date: Wed Jul 19 14:08:52 2023 +0000

bpf: Add fd-based tcx multi-prog infra with link support

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=13dfaae6a80000
start commit: 03b123debcbc tcp: tcp_enter_quickack_mode() should be static
git tree: net-next
final oops: https://syzkaller.appspot.com/x/report.txt?x=103faae6a80000
console output: https://syzkaller.appspot.com/x/log.txt?x=17dfaae6a80000
kernel config: https://syzkaller.appspot.com/x/.config?x=32e3dcc11fd0d297
dashboard link: https://syzkaller.appspot.com/bug?extid=b202b7208664142954fa
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=15cc32e6a80000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=16aace14a80000

Reported-by: syzbot+b202b7...@syzkaller.appspotmail.com
Fixes: e420bed02507 ("bpf: Add fd-based tcx multi-prog infra with link support")

For information about bisection process see: https://goo.gl/tpsmEJ#bisection

[syzbot]

> #syz test: https://github.com/cilium/linux.git pr/new-api-tcx8

Your commands are accepted, but please keep syzkall...@googlegroups.com mailing list in CC next time. It serves as a history of what happened with each bug report. Thank you.

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-and-tested-by: syzbot+b202b7...@syzkaller.appspotmail.com

Tested on:

commit: 2542a961 tcx: Fix splat in ingress_destroy upon tcx_en..
git tree: https://github.com/cilium/linux.git pr/new-api-tcx8
console output: https://syzkaller.appspot.com/x/log.txt?x=108b2614a80000
kernel config: https://syzkaller.appspot.com/x/.config?x=23b50c2e795c7120
dashboard link: https://syzkaller.appspot.com/bug?extid=b202b7208664142954fa
compiler: gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40

Note: no patches were applied.
Note: testing is done by a robot and is best-effort only.