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KASAN: use-after-free Read in qdisc_pkt_len_segs_init

Status: upstream: reported on 2026/04/14 11:58
Subsystems: bridge
[Documentation on labels]
Reported-by: syzbot+83181a31faf9455499c5@syzkaller.appspotmail.com
First crash: 32d, last: 14h43m
▶ ▼ Discussions (4)
Title Replies (including bot) Last reply
[syzbot] Monthly bridge report (May 2026) 0 (1) 2026/05/08 20:32
[PATCH net v2] net: iptunnel: fix stale transport header after GRE/TEB decap 5 (5) 2026/04/24 02:04
[PATCH net v1 1/2] net: tunnel: fix stale transport header after GRE/TEB decap 1 (1) 2026/04/16 03:46
[syzbot] [bridge?] KASAN: use-after-free Read in qdisc_pkt_len_segs_init 0 (1) 2026/04/14 11:58

Sample crash report:
==================================================================
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+0xa51/0xb30 net/core/dev.c:4140
Read of size 2 at addr ffff88816a8813f4 by task syz.7.3518/14796

CPU: 1 UID: 0 PID: 14796 Comm: syz.7.3518 Tainted: G             L      syzkaller #0 PREEMPT(full) 
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
Call Trace:
 <IRQ>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x100/0x190 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:378 [inline]
 print_report+0x13d/0x4b0 mm/kasan/report.c:482
 kasan_report+0xdf/0x1d0 mm/kasan/report.c:595
 __tcp_hdrlen include/linux/tcp.h:31 [inline]
 qdisc_pkt_len_segs_init+0xa51/0xb30 net/core/dev.c:4140
 __dev_queue_xmit+0x270/0x4950 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+0xdcf/0x28a0 net/hsr/hsr_forward.c:743
 hsr_handle_frame+0x82f/0xac0 net/hsr/hsr_slave.c:81
 __netif_receive_skb_core.constprop.0+0x6c5/0x3530 net/core/dev.c:6089
 __netif_receive_skb_list_core+0x353/0x940 net/core/dev.c:6277
 __netif_receive_skb_list net/core/dev.c:6344 [inline]
 netif_receive_skb_list_internal+0x722/0xd40 net/core/dev.c:6435
 gro_normal_list include/net/gro.h:523 [inline]
 gro_normal_list include/net/gro.h:519 [inline]
 gro_flush_normal include/net/gro.h:531 [inline]
 napi_complete_done+0x221/0x940 net/core/dev.c:6803
 gro_cell_poll+0x46e/0x690 net/core/gro_cells.c:74
 __napi_poll.constprop.0+0xaf/0x450 net/core/dev.c:7730
 napi_poll net/core/dev.c:7793 [inline]
 net_rx_action+0xa40/0xf20 net/core/dev.c:7950
 handle_softirqs+0x1ea/0xa00 kernel/softirq.c:622
 do_softirq kernel/softirq.c:523 [inline]
 do_softirq+0xac/0xe0 kernel/softirq.c:510
 </IRQ>
 <TASK>
 __local_bh_enable_ip+0xf8/0x120 kernel/softirq.c:450
 local_bh_enable include/linux/bottom_half.h:33 [inline]
 tun_rx_batched.isra.0+0x407/0x750 drivers/net/tun.c:1512
 tun_get_user+0x1e31/0x3c20 drivers/net/tun.c:1955
 tun_chr_write_iter+0xdc/0x200 drivers/net/tun.c:2001
 new_sync_write fs/read_write.c:595 [inline]
 vfs_write+0x6ac/0x1070 fs/read_write.c:688
 ksys_write+0x12a/0x250 fs/read_write.c:740
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x10b/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f08fdf9cdd9
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:00007f08fef34028 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f08fe215fa0 RCX: 00007f08fdf9cdd9
RDX: 000000000000fdef RSI: 00002000000002c0 RDI: 0000000000000003
RBP: 00007f08fe032d69 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f08fe216038 R14: 00007f08fe215fa0 R15: 00007fffcb47f238
 </TASK>

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x16a881
flags: 0x57ff00000000000(node=1|zone=2|lastcpupid=0x7ff)
raw: 057ff00000000000 ffffea0005aa2048 ffffea0005aa2048 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:
 ffff88816a881280: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff88816a881300: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff88816a881380: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                                                             ^
 ffff88816a881400: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff88816a881480: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
==================================================================

Crashes (29):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/05/07 18:18 upstream 19cbc75c56c0 e358bca5 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-selinux-root KASAN: use-after-free Read in qdisc_pkt_len_segs_init
2026/05/07 06:54 upstream 5862221fdded f250db59 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-selinux-root KASAN: use-after-free Read in qdisc_pkt_len_segs_init
2026/05/06 20:46 upstream adc1e5c6203c cbcd9ea0 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-selinux-root KASAN: use-after-free Read in qdisc_pkt_len_segs_init
2026/04/26 21:18 upstream 897d54018cc9 9c2d0995 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-selinux-root KASAN: use-after-free Read in qdisc_pkt_len_segs_init
2026/04/21 16:42 upstream b4e07588e743 0b6ab7ec .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce KASAN: use-after-free Read in qdisc_pkt_len_segs_init
2026/04/23 08:15 upstream 2a4c0c11c019 b10da5ec .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-386 KASAN: use-after-free Read in qdisc_pkt_len_segs_init
2026/04/19 07:16 upstream eb5249b12507 303e2802 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-386 KASAN: use-after-free Read in qdisc_pkt_len_segs_init
2026/05/06 00:42 upstream 9207d47f966b 26da2c66 .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream KASAN: use-after-free Read in qdisc_pkt_len_segs_init
2026/05/05 09:13 upstream a293ec25d59d 114c483e .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream KASAN: use-after-free Read in qdisc_pkt_len_segs_init
2026/05/04 21:45 upstream c7e4e4d5f7dc a898ba9c .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream KASAN: use-after-free Read in qdisc_pkt_len_segs_init
2026/05/04 09:56 upstream 6d35786de281 85f1bcf2 .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream KASAN: use-after-free Read in qdisc_pkt_len_segs_init
2026/05/01 12:21 upstream 26fd6bff2c05 753c55b9 .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream KASAN: use-after-free Read in qdisc_pkt_len_segs_init
2026/04/24 14:08 upstream dd6c438c3e64 629ff21a .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream KASAN: use-after-free Read in qdisc_pkt_len_segs_init
2026/04/24 13:29 upstream dd6c438c3e64 629ff21a .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream KASAN: use-after-free Read in qdisc_pkt_len_segs_init
2026/04/17 02:41 upstream 3cd8b194bf34 de0a551d .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream KASAN: use-after-free Read in qdisc_pkt_len_segs_init
2026/05/08 11:17 net fcee7d82f27d 5633175a .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-net-this-kasan-gce KASAN: use-after-free Read in qdisc_pkt_len_segs_init
2026/05/08 02:15 net 41ae14071cd7 e358bca5 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-net-this-kasan-gce KASAN: use-after-free Read in qdisc_pkt_len_segs_init
2026/05/07 22:15 net 41ae14071cd7 e358bca5 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-net-this-kasan-gce KASAN: use-after-free Read in qdisc_pkt_len_segs_init
2026/05/12 00:56 net-next 63751099502d d168f260 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-net-kasan-gce KASAN: use-after-free Read in qdisc_pkt_len_segs_init
2026/05/05 00:32 net-next 98878ed91b68 a898ba9c .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-net-kasan-gce KASAN: use-after-free Read in qdisc_pkt_len_segs_init
2026/05/01 14:33 net-next edf4bee4215a 753c55b9 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-net-kasan-gce KASAN: use-after-free Read in qdisc_pkt_len_segs_init
2026/04/26 21:59 net-next e728258debd5 9c2d0995 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-net-kasan-gce KASAN: use-after-free Read in qdisc_pkt_len_segs_init
2026/04/24 10:28 net-next e728258debd5 9cfb3ca7 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-net-kasan-gce KASAN: use-after-free Read in qdisc_pkt_len_segs_init
2026/04/18 13:32 net-next 1f5ffc672165 303e2802 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-net-kasan-gce KASAN: use-after-free Read in qdisc_pkt_len_segs_init
2026/04/13 00:48 net-next 17ad4759a082 38c8e246 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-net-kasan-gce KASAN: use-after-free Read in qdisc_pkt_len_segs_init
2026/04/12 20:25 net-next 17ad4759a082 38c8e246 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-net-kasan-gce KASAN: use-after-free Read in qdisc_pkt_len_segs_init
2026/04/10 01:30 net-next 9700282a7ec7 38c8e246 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-net-kasan-gce KASAN: use-after-free Read in qdisc_pkt_len_segs_init
2026/04/25 07:10 upstream 27d128c1cff6 9c2d0995 .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream-386 BUG: unable to handle kernel paging request in qdisc_pkt_len_segs_init
2026/04/24 00:33 upstream 2e6803928193 629ff21a .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream-386 BUG: unable to handle kernel paging request in qdisc_pkt_len_segs_init
* Struck through repros no longer work on HEAD.