[syzbot] [can?] WARNING: refcount bug in sk_skb_reason_drop

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    a430d95c5efa Merge tag 'lsm-pr-20240911' of git://git.kern..
git tree:       upstream
console+strace: https://syzkaller.appspot.com/x/log.txt?x=11260ca9980000
kernel config:  https://syzkaller.appspot.com/x/.config?x=d85e1e571a820894
dashboard link: https://syzkaller.appspot.com/bug?extid=d4e8dc385d9258220c31
compiler:       gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=11903177980000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=15b9a607980000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/4faaa939b3a4/disk-a430d95c.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/83c722076440/vmlinux-a430d95c.xz
kernel image: https://storage.googleapis.com/syzbot-assets/24c938d49c40/bzImage-a430d95c.xz

The issue was bisected to:

commit c9c0ee5f20c593faf289fa8850c3ed84031dd12a
Author: Breno Leitao <leitao@xxxxxxxxxx>
Date:   Mon Jul 29 10:47:40 2024 +0000

    net: skbuff: Skip early return in skb_unref when debugging

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=15e6f69f980000
final oops:     https://syzkaller.appspot.com/x/report.txt?x=17e6f69f980000
console output: https://syzkaller.appspot.com/x/log.txt?x=13e6f69f980000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+d4e8dc385d9258220c31@xxxxxxxxxxxxxxxxxxxxxxxxx
Fixes: c9c0ee5f20c5 ("net: skbuff: Skip early return in skb_unref when debugging")

vxcan1: j1939_tp_rxtimer: 0xffff8880326cb400: rx timeout, send abort
vxcan1: j1939_xtp_rx_abort_one: 0xffff8880326cb400: 0x00000: (3) A timeout occurred and this is the connection abort to close the session.
------------[ cut here ]------------
refcount_t: underflow; use-after-free.
WARNING: CPU: 0 PID: 16 at lib/refcount.c:28 refcount_warn_saturate+0x14a/0x210 lib/refcount.c:28
Modules linked in:
CPU: 0 UID: 0 PID: 16 Comm: ksoftirqd/0 Not tainted 6.11.0-syzkaller-02574-ga430d95c5efa #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/06/2024
RIP: 0010:refcount_warn_saturate+0x14a/0x210 lib/refcount.c:28
Code: ff 89 de e8 58 80 04 fd 84 db 0f 85 66 ff ff ff e8 6b 7e 04 fd c6 05 59 3d 7f 0b 01 90 48 c7 c7 00 ba b0 8b e8 67 d1 c6 fc 90 <0f> 0b 90 90 e9 43 ff ff ff e8 48 7e 04 fd 0f b6 1d 34 3d 7f 0b 31
RSP: 0018:ffffc900001577c8 EFLAGS: 00010286
RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffffffff814e2c79
RDX: ffff88801cadda00 RSI: ffffffff814e2c86 RDI: 0000000000000001
RBP: ffff88802e405224 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000002
R13: 0000000000000000 R14: ffff88802e405224 R15: 0000000000000001
FS:  0000000000000000(0000) GS:ffff8880b8800000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000055772d12ee40 CR3: 000000002853a000 CR4: 0000000000350ef0
Call Trace:
 <TASK>
 __refcount_sub_and_test include/linux/refcount.h:275 [inline]
 __refcount_dec_and_test include/linux/refcount.h:307 [inline]
 refcount_dec_and_test include/linux/refcount.h:325 [inline]
 skb_unref include/linux/skbuff.h:1232 [inline]
 __sk_skb_reason_drop net/core/skbuff.c:1213 [inline]
 sk_skb_reason_drop+0x183/0x1a0 net/core/skbuff.c:1241
 kfree_skb_reason include/linux/skbuff.h:1262 [inline]
 kfree_skb include/linux/skbuff.h:1271 [inline]
 j1939_session_destroy+0x163/0x460 net/can/j1939/transport.c:282
 __j1939_session_release net/can/j1939/transport.c:294 [inline]
 kref_put include/linux/kref.h:65 [inline]
 j1939_session_put net/can/j1939/transport.c:299 [inline]
 j1939_xtp_rx_abort_one+0x3f9/0x560 net/can/j1939/transport.c:1354
 j1939_xtp_rx_abort net/can/j1939/transport.c:1362 [inline]
 j1939_tp_cmd_recv net/can/j1939/transport.c:2128 [inline]
 j1939_tp_recv+0xcf8/0xf50 net/can/j1939/transport.c:2161
 j1939_can_recv+0x78f/0xa50 net/can/j1939/main.c:108
 deliver net/can/af_can.c:572 [inline]
 can_rcv_filter+0x2ab/0x900 net/can/af_can.c:606
 can_receive+0x320/0x5c0 net/can/af_can.c:663
 can_rcv+0x1e2/0x280 net/can/af_can.c:687
 __netif_receive_skb_one_core+0x1b4/0x1e0 net/core/dev.c:5662
 __netif_receive_skb+0x1d/0x160 net/core/dev.c:5775
 process_backlog+0x443/0x15f0 net/core/dev.c:6107
 __napi_poll.constprop.0+0xba/0x550 net/core/dev.c:6771
 napi_poll net/core/dev.c:6840 [inline]
 net_rx_action+0xa92/0x1010 net/core/dev.c:6962
 handle_softirqs+0x219/0x8f0 kernel/softirq.c:554
 run_ksoftirqd kernel/softirq.c:928 [inline]
 run_ksoftirqd+0x3a/0x60 kernel/softirq.c:920
 smpboot_thread_fn+0x664/0xa10 kernel/smpboot.c:164
 kthread+0x2c4/0x3a0 kernel/kthread.c:389
 ret_from_fork+0x48/0x80 arch/x86/kernel/process.c:147
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
 </TASK>


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