Subject: Re: [syzbot] kernel BUG in pskb_expand_head

From: syzbot <[email-masked]>
Date: Wed, 05 Jan 2022 03:20:26 -0800

syzbot has found a reproducer for the following issue on:

HEAD commit:    c9e6606c7fe9 Linux 5.16-rc8
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=148351c3b00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=32f9fa260d7413b4
dashboard link: https://syzkaller.appspot.com/bug?extid=4c63f36709a642f801c5
compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=15435e2bb00000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=12f4508db00000

The issue was bisected to:

commit e4b8954074f6d0db01c8c97d338a67f9389c042f
Author: Eric Dumazet <[email-masked]>
Date:   Tue Dec 7 01:30:37 2021 +0000

    netlink: add net device refcount tracker to struct ethnl_req_info

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=109e6fcbb00000
final oops:     https://syzkaller.appspot.com/x/report.txt?x=129e6fcbb00000
console output: https://syzkaller.appspot.com/x/log.txt?x=149e6fcbb00000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: [email-masked]
Fixes: e4b8954074f6 ("netlink: add net device refcount tracker to struct ethnl_req_info")

skbuff: skb_over_panic: text:ffffffff88235fb8 len:4096 put:4096 head:ffff888021cb8400 data:ffff888021cb8400 tail:0x1000 end:0xc0 dev:<NULL>
------------[ cut here ]------------
kernel BUG at net/core/skbuff.c:113!
invalid opcode: 0000 [#1] PREEMPT SMP KASAN
CPU: 1 PID: 19 Comm: ksoftirqd/1 Not tainted 5.16.0-rc8-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:skb_panic+0x16c/0x16e net/core/skbuff.c:113
Code: f8 4c 8b 4c 24 10 8b 4b 70 41 56 45 89 e8 4c 89 e2 41 57 48 89 ee 48 c7 c7 e0 4b ad 8a ff 74 24 10 ff 74 24 20 e8 6e 24 c2 ff <0f> 0b e8 74 92 38 f8 4c 8b 64 24 18 e8 da 47 7f f8 48 c7 c1 80 58
RSP: 0018:ffffc90000d979e0 EFLAGS: 00010286
RAX: 000000000000008b RBX: ffff888021ccb500 RCX: 0000000000000000
RDX: ffff88801196d700 RSI: ffffffff815f0948 RDI: fffff520001b2f2e
RBP: ffffffff8aad58c0 R08: 000000000000008b R09: 0000000000000000
R10: ffffffff815ea6ee R11: 0000000000000000 R12: ffffffff88235fb8
R13: 0000000000001000 R14: ffffffff8aad4ba0 R15: 00000000000000c0
FS:  0000000000000000(0000) GS:ffff8880b9d00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f886c8cc718 CR3: 000000007ad6d000 CR4: 00000000003506e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 skb_over_panic net/core/skbuff.c:118 [inline]
 skb_put.cold+0x24/0x24 net/core/skbuff.c:1990
 isotp_rcv_cf net/can/isotp.c:570 [inline]
 isotp_rcv+0xa38/0x1e30 net/can/isotp.c:668
 deliver net/can/af_can.c:574 [inline]
 can_rcv_filter+0x445/0x8d0 net/can/af_can.c:635
 can_receive+0x31d/0x580 net/can/af_can.c:665
 can_rcv+0x120/0x1c0 net/can/af_can.c:696
 __netif_receive_skb_one_core+0x114/0x180 net/core/dev.c:5465
 __netif_receive_skb+0x24/0x1b0 net/core/dev.c:5579
 process_backlog+0x2a5/0x6c0 net/core/dev.c:6455
 __napi_poll+0xaf/0x440 net/core/dev.c:7023
 napi_poll net/core/dev.c:7090 [inline]
 net_rx_action+0x801/0xb40 net/core/dev.c:7177
 __do_softirq+0x29b/0x9c2 kernel/softirq.c:558
 run_ksoftirqd kernel/softirq.c:921 [inline]
 run_ksoftirqd+0x2d/0x60 kernel/softirq.c:913
 smpboot_thread_fn+0x645/0x9c0 kernel/smpboot.c:164
 kthread+0x405/0x4f0 kernel/kthread.c:327
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295
 </TASK>
Modules linked in:
---[ end trace 9f06028ec4daf4be ]---
RIP: 0010:skb_panic+0x16c/0x16e net/core/skbuff.c:113
Code: f8 4c 8b 4c 24 10 8b 4b 70 41 56 45 89 e8 4c 89 e2 41 57 48 89 ee 48 c7 c7 e0 4b ad 8a ff 74 24 10 ff 74 24 20 e8 6e 24 c2 ff <0f> 0b e8 74 92 38 f8 4c 8b 64 24 18 e8 da 47 7f f8 48 c7 c1 80 58
RSP: 0018:ffffc90000d979e0 EFLAGS: 00010286
RAX: 000000000000008b RBX: ffff888021ccb500 RCX: 0000000000000000
RDX: ffff88801196d700 RSI: ffffffff815f0948 RDI: fffff520001b2f2e
RBP: ffffffff8aad58c0 R08: 000000000000008b R09: 0000000000000000
R10: ffffffff815ea6ee R11: 0000000000000000 R12: ffffffff88235fb8
R13: 0000000000001000 R14: ffffffff8aad4ba0 R15: 00000000000000c0
FS:  0000000000000000(0000) GS:ffff8880b9d00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f886c8cc718 CR3: 000000007ad6d000 CR4: 00000000003506e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400