From: syzbot <syzbot+83181a31faf9455499c5@syzkaller.appspotmail.com>
To: bridge@lists.linux.dev, davem@davemloft.net, dsahern@kernel.org,
edumazet@google.com, horms@kernel.org, idosch@nvidia.com,
jiayuan.chen@linux.dev, kuba@kernel.org,
linux-kernel@vger.kernel.org, netdev@vger.kernel.org,
pabeni@redhat.com, pshelar@nicira.com, razor@blackwall.org,
syzkaller-bugs@googlegroups.com, tom@herbertland.com
Subject: Re: [syzbot] [bridge?] KASAN: use-after-free Read in qdisc_pkt_len_segs_init
Date: Fri, 05 Jun 2026 09:58:25 -0700 [thread overview]
Message-ID: <6a230031.39669fcc.2372e3.0003.GAE@google.com> (raw)
In-Reply-To: <69de2bee.a00a0220.475f0.0041.GAE@google.com>
syzbot has found a reproducer for the following issue on:
HEAD commit: 4aacf509e537 net: mv643xx: fix OF node refcount
git tree: net
console output: https://syzkaller.appspot.com/x/log.txt?x=15b8fdd2580000
kernel config: https://syzkaller.appspot.com/x/.config?x=65472e27d1590a04
dashboard link: https://syzkaller.appspot.com/bug?extid=83181a31faf9455499c5
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=10a6da86580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=13a3c0ae580000
Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/7559c887601e/disk-4aacf509.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/185ea069b480/vmlinux-4aacf509.xz
kernel image: https://storage.googleapis.com/syzbot-assets/4285524349b9/bzImage-4aacf509.xz
IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+83181a31faf9455499c5@syzkaller.appspotmail.com
==================================================================
BUG: KASAN: use-after-free in __tcp_hdrlen include/linux/tcp.h:31 [inline]
BUG: KASAN: use-after-free in qdisc_pkt_len_segs_init+0x7f8/0xa30 net/core/dev.c:4140
Read of size 2 at addr ffff88817cd41734 by task syz.0.17/5856
CPU: 0 UID: 0 PID: 5856 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
Call Trace:
<IRQ>
dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
print_address_description+0x55/0x1e0 mm/kasan/report.c:378
print_report+0x58/0x70 mm/kasan/report.c:482
kasan_report+0x117/0x150 mm/kasan/report.c:595
__tcp_hdrlen include/linux/tcp.h:31 [inline]
qdisc_pkt_len_segs_init+0x7f8/0xa30 net/core/dev.c:4140
__dev_queue_xmit+0x29a/0x3950 net/core/dev.c:4782
dev_queue_xmit include/linux/netdevice.h:3418 [inline]
hsr_xmit net/hsr/hsr_forward.c:440 [inline]
hsr_forward_do net/hsr/hsr_forward.c:581 [inline]
hsr_forward_skb+0x167e/0x2ab0 net/hsr/hsr_forward.c:743
hsr_handle_frame+0x6b8/0xa50 net/hsr/hsr_slave.c:81
__netif_receive_skb_core+0x98f/0x3170 net/core/dev.c:6089
__netif_receive_skb_list_core+0x24d/0x810 net/core/dev.c:6277
__netif_receive_skb_list net/core/dev.c:6344 [inline]
netif_receive_skb_list_internal+0x995/0xcf0 net/core/dev.c:6435
gro_normal_list include/net/gro.h:523 [inline]
gro_flush_normal include/net/gro.h:531 [inline]
napi_complete_done+0x299/0x730 net/core/dev.c:6803
gro_cell_poll+0x5a9/0x5d0 net/core/gro_cells.c:74
__napi_poll+0xae/0x340 net/core/dev.c:7733
napi_poll net/core/dev.c:7796 [inline]
net_rx_action+0x627/0xf70 net/core/dev.c:7953
handle_softirqs+0x22a/0x840 kernel/softirq.c:622
do_softirq+0x76/0xd0 kernel/softirq.c:523
</IRQ>
<TASK>
__local_bh_enable_ip+0xf8/0x130 kernel/softirq.c:450
local_bh_enable include/linux/bottom_half.h:33 [inline]
tun_rx_batched+0x617/0x790 drivers/net/tun.c:-1
tun_get_user+0x2bbc/0x43e0 drivers/net/tun.c:1955
tun_chr_write_iter+0x113/0x200 drivers/net/tun.c:2001
new_sync_write fs/read_write.c:595 [inline]
vfs_write+0x61d/0xb90 fs/read_write.c:688
ksys_write+0x150/0x270 fs/read_write.c:740
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x174/0x580 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fe91fb9ce59
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 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 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffda826a2e8 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007fe91fe15fa0 RCX: 00007fe91fb9ce59
RDX: 000000000000007a RSI: 00002000000002c0 RDI: 0000000000000005
RBP: 00007fe91fc32d6f R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fe91fe15fac R14: 00007fe91fe15fa0 R15: 00007fe91fe15fa0
</TASK>
The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x17cd41
flags: 0x57ff00000000000(node=1|zone=2|lastcpupid=0x7ff)
raw: 057ff00000000000 ffffea0005f35048 ffffea0005f35048 0000000000000000
raw: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner info is not present (never set?)
Memory state around the buggy address:
ffff88817cd41600: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
ffff88817cd41680: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff88817cd41700: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
^
ffff88817cd41780: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
ffff88817cd41800: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
==================================================================
---
If you want syzbot to run the reproducer, reply with:
#syz test: git://repo/address.git branch-or-commit-hash
If you attach or paste a git patch, syzbot will apply it before testing.
prev parent reply other threads:[~2026-06-05 16:58 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-04-14 11:58 [syzbot] [bridge?] KASAN: use-after-free Read in qdisc_pkt_len_segs_init syzbot
2026-06-05 16:58 ` syzbot [this message]
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