KASAN: use-after-free Read in l2tp_xmit_skb

Status: premoderation: reported on 2026/10/14 07:15
Reported-by: syzbot+95fc20ec448892788d9f@syzkaller.appspotmail.com
First crash: 1d05h, last: 1d05h
▶ ▼ Similar bugs (3)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
android-5-10 KASAN: use-after-free Read in l2tp_xmit_skb 19 1 47d 47d 0/2 premoderation: reported on 2026/08/28 15:04
android-6-1 KASAN: use-after-free Read in l2tp_xmit_skb 19 2 108d 120d 0/2 auto-obsoleted due to no activity on 2026/09/26 16:10
android-6-1 KASAN: use-after-free Read in l2tp_xmit_skb (2) 19 1 3d15h 3d15h 0/2 premoderation: reported on 2026/10/11 21:04

Sample crash report:
==================================================================
BUG: KASAN: use-after-free in l2tp_xmit_core net/l2tp/l2tp_core.c:-1 [inline]
BUG: KASAN: use-after-free in l2tp_xmit_skb+0x1038/0x1770 net/l2tp/l2tp_core.c:1137
Read of size 2 at addr ffff888129ede03a by task syz.2.350/1452

CPU: 0 PID: 1452 Comm: syz.2.350 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/16/2026
Call Trace:
 <TASK>
 __dump_stack+0x21/0x30 lib/dump_stack.c:88
 dump_stack_lvl+0x110/0x170 lib/dump_stack.c:106
 print_address_description+0x7f/0x2c0 mm/kasan/report.c:248
 __kasan_report mm/kasan/report.c:427 [inline]
 kasan_report+0x10f/0x150 mm/kasan/report.c:444
 __asan_report_load2_noabort+0x14/0x20 mm/kasan/report_generic.c:307
 l2tp_xmit_core net/l2tp/l2tp_core.c:-1 [inline]
 l2tp_xmit_skb+0x1038/0x1770 net/l2tp/l2tp_core.c:1137
 pppol2tp_sendmsg+0x35a/0x5f0 net/l2tp/l2tp_ppp.c:308
 sock_sendmsg_nosec net/socket.c:704 [inline]
 __sock_sendmsg net/socket.c:716 [inline]
 ____sys_sendmsg+0x5be/0x8f0 net/socket.c:2436
 ___sys_sendmsg+0x236/0x2e0 net/socket.c:2490
 __sys_sendmmsg+0x2ba/0x4e0 net/socket.c:2576
 __do_sys_sendmmsg net/socket.c:2605 [inline]
 __se_sys_sendmmsg net/socket.c:2602 [inline]
 __x64_sys_sendmmsg+0xa0/0xb0 net/socket.c:2602
 x64_sys_call+0x6c6/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:308
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7f0927bb22d9
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:00007f092660b028 EFLAGS: 00000246 ORIG_RAX: 0000000000000133
RAX: ffffffffffffffda RBX: 00007f0927e39fa0 RCX: 00007f0927bb22d9
RDX: 0000000000034000 RSI: 0000200000004380 RDI: 0000000000000004
RBP: 00007f0927c49888 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f0927e3a038 R14: 00007f0927e39fa0 R15: 00007fffe688edf8
 </TASK>

Allocated by task 1452:
 kasan_save_stack mm/kasan/common.c:38 [inline]
 kasan_set_track mm/kasan/common.c:45 [inline]
 set_alloc_info mm/kasan/common.c:433 [inline]
 ____kasan_kmalloc mm/kasan/common.c:512 [inline]
 __kasan_kmalloc+0xd4/0x100 mm/kasan/common.c:521
 kasan_kmalloc include/linux/kasan.h:227 [inline]
 __kmalloc+0x13d/0x2c0 mm/slub.c:4436
 kmalloc include/linux/slab.h:624 [inline]
 kzalloc include/linux/slab.h:750 [inline]
 l2tp_session_create+0x39/0xb60 net/l2tp/l2tp_core.c:1616
 pppol2tp_connect+0xbf5/0x1640 net/l2tp/l2tp_ppp.c:772
 __sys_connect_file net/socket.c:1923 [inline]
 __sys_connect+0x3cb/0x450 net/socket.c:1940
 __do_sys_connect net/socket.c:1950 [inline]
 __se_sys_connect net/socket.c:1947 [inline]
 __x64_sys_connect+0x7a/0x90 net/socket.c:1947
 x64_sys_call+0x7c/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:43
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x66/0xd0

Freed by task 1473:
 kasan_save_stack mm/kasan/common.c:38 [inline]
 kasan_set_track+0x4a/0x70 mm/kasan/common.c:45
 kasan_set_free_info+0x23/0x40 mm/kasan/generic.c:370
 ____kasan_slab_free+0x125/0x160 mm/kasan/common.c:365
 __kasan_slab_free+0x11/0x20 mm/kasan/common.c:373
 kasan_slab_free include/linux/kasan.h:193 [inline]
 slab_free_hook mm/slub.c:1728 [inline]
 slab_free_freelist_hook+0xc2/0x190 mm/slub.c:1754
 slab_free mm/slub.c:3526 [inline]
 kfree+0xc4/0x270 mm/slub.c:4588
 l2tp_session_free net/l2tp/l2tp_core.c:168 [inline]
 l2tp_session_put+0xaf/0x1a0 net/l2tp/l2tp_core.c:193
 pppol2tp_ioctl+0x748/0x960 net/l2tp/l2tp_ppp.c:-1
 pppox_ioctl+0x1e1/0x440 drivers/net/ppp/pppox.c:110
 sock_do_ioctl+0x103/0x310 net/socket.c:1138
 sock_ioctl+0x459/0x6d0 net/socket.c:1257
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:874 [inline]
 __se_sys_ioctl+0x121/0x1a0 fs/ioctl.c:860
 __x64_sys_ioctl+0x7b/0x90 fs/ioctl.c:860
 x64_sys_call+0x2f/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:17
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x66/0xd0

The buggy address belongs to the object at ffff888129ede000
 which belongs to the cache kmalloc-512 of size 512
The buggy address is located 58 bytes inside of
 512-byte region [ffff888129ede000, ffff888129ede200)
The buggy address belongs to the page:
page:ffffea0004a7b700 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x129edc
head:ffffea0004a7b700 order:2 compound_mapcount:0 compound_pincount:0
flags: 0x4000000000010200(slab|head|zone=1)
raw: 4000000000010200 0000000000000000 0000000100000001 ffff888100042f00
raw: 0000000000000000 0000000000100010 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 2, migratetype Unmovable, gfp_mask 0x1d2a20(GFP_ATOMIC|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC|__GFP_HARDWALL), pid 316, ts 28069848019, free_ts 0
 set_page_owner include/linux/page_owner.h:33 [inline]
 post_alloc_hook+0x192/0x1b0 mm/page_alloc.c:2607
 prep_new_page+0x1c/0x110 mm/page_alloc.c:2613
 get_page_from_freelist+0x2c3a/0x2cd0 mm/page_alloc.c:4487
 __alloc_pages+0x1a2/0x460 mm/page_alloc.c:5824
 alloc_slab_page mm/slub.c:-1 [inline]
 allocate_slab mm/slub.c:1937 [inline]
 new_slab+0xa0/0x4d0 mm/slub.c:2000
 ___slab_alloc+0x3ac/0x840 mm/slub.c:3033
 __slab_alloc+0x49/0x90 mm/slub.c:3120
 slab_alloc_node mm/slub.c:3211 [inline]
 slab_alloc mm/slub.c:3255 [inline]
 __kmalloc_track_caller+0x169/0x2c0 mm/slub.c:4954
 kmalloc_reserve net/core/skbuff.c:357 [inline]
 __alloc_skb+0x210/0x730 net/core/skbuff.c:428
 alloc_skb include/linux/skbuff.h:1183 [inline]
 pfkey_send_acquire+0x61a/0x2eb0 net/key/af_key.c:3203
 km_query+0x6c/0xd0 net/xfrm/xfrm_state.c:2251
 xfrm_state_find+0x1e7e/0x2a10 net/xfrm/xfrm_state.c:1164
 xfrm_tmpl_resolve_one net/xfrm/xfrm_policy.c:2390 [inline]
 xfrm_tmpl_resolve net/xfrm/xfrm_policy.c:2435 [inline]
 xfrm_resolve_and_create_bundle+0x6b7/0x2a20 net/xfrm/xfrm_policy.c:2728
 xfrm_bundle_lookup net/xfrm/xfrm_policy.c:2963 [inline]
 xfrm_lookup_with_ifid+0x692/0x2050 net/xfrm/xfrm_policy.c:3094
 xfrm_lookup net/xfrm/xfrm_policy.c:3191 [inline]
 xfrm_lookup_route+0x3c/0x170 net/xfrm/xfrm_policy.c:3202
 ip6_dst_lookup_flow net/ipv6/ip6_output.c:1240 [inline]
 ip6_sk_dst_lookup_flow+0x5fe/0x840 net/ipv6/ip6_output.c:1272
page_owner free stack trace missing

Memory state around the buggy address:
 ffff888129eddf00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff888129eddf80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff888129ede000: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                        ^
 ffff888129ede080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff888129ede100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================
------------[ cut here ]------------
WARNING: CPU: 1 PID: 1452 at net/l2tp/l2tp_ppp.c:156 pppol2tp_sock_to_session+0x167/0x1b0 net/l2tp/l2tp_ppp.c:156
Modules linked in:
CPU: 1 PID: 1452 Comm: syz.2.350 Tainted: G    B             syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/16/2026
RIP: 0010:pppol2tp_sock_to_session+0x167/0x1b0 net/l2tp/l2tp_ppp.c:156
Code: 5d c3 e8 8c ab 0a fd be 02 00 00 00 eb 0a e8 80 ab 0a fd be 01 00 00 00 4c 89 f7 e8 73 2e f1 fd e9 0f ff ff ff e8 69 ab 0a fd <0f> 0b 48 89 df e8 ef 00 00 00 eb bd e8 58 ab 0a fd 4c 89 f7 be 03
RSP: 0018:ffffc90000d47898 EFLAGS: 00010293
RAX: ffffffff845f3077 RBX: ffff8881011d9000 RCX: ffff88810dfebc00
RDX: 0000000000000000 RSI: 0000000011ed3330 RDI: 000000000c04eb7d
RBP: ffffc90000d478b8 R08: ffff8881011d9083 R09: 1ffff1102023b210
R10: dffffc0000000000 R11: ffffed102023b211 R12: dffffc0000000000
R13: 0000000000000000 R14: 0000000011ed3330 R15: ffff888129ede000
FS:  00007f092660b6c0(0000) GS:ffff8881f7100000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000055556b764908 CR3: 000000011b398000 CR4: 00000000003506a0
Call Trace:
 <TASK>
 pppol2tp_sendmsg+0xdf/0x5f0 net/l2tp/l2tp_ppp.c:271
 sock_sendmsg_nosec net/socket.c:704 [inline]
 __sock_sendmsg net/socket.c:716 [inline]
 ____sys_sendmsg+0x5be/0x8f0 net/socket.c:2436
 ___sys_sendmsg+0x236/0x2e0 net/socket.c:2490
 __sys_sendmmsg+0x2ba/0x4e0 net/socket.c:2576
 __do_sys_sendmmsg net/socket.c:2605 [inline]
 __se_sys_sendmmsg net/socket.c:2602 [inline]
 __x64_sys_sendmmsg+0xa0/0xb0 net/socket.c:2602
 x64_sys_call+0x6c6/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:308
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7f0927bb22d9
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:00007f092660b028 EFLAGS: 00000246 ORIG_RAX: 0000000000000133
RAX: ffffffffffffffda RBX: 00007f0927e39fa0 RCX: 00007f0927bb22d9
RDX: 0000000000034000 RSI: 0000200000004380 RDI: 0000000000000004
RBP: 00007f0927c49888 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f0927e3a038 R14: 00007f0927e39fa0 R15: 00007fffe688edf8
 </TASK>
---[ end trace 7d3744080dca6df3 ]---
------------[ cut here ]------------
WARNING: CPU: 0 PID: 1452 at net/l2tp/l2tp_ppp.c:156 pppol2tp_sock_to_session+0x167/0x1b0 net/l2tp/l2tp_ppp.c:156
Modules linked in:
CPU: 0 PID: 1452 Comm: syz.2.350 Tainted: G    B   W         syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/16/2026
RIP: 0010:pppol2tp_sock_to_session+0x167/0x1b0 net/l2tp/l2tp_ppp.c:156
Code: 5d c3 e8 8c ab 0a fd be 02 00 00 00 eb 0a e8 80 ab 0a fd be 01 00 00 00 4c 89 f7 e8 73 2e f1 fd e9 0f ff ff ff e8 69 ab 0a fd <0f> 0b 48 89 df e8 ef 00 00 00 eb bd e8 58 ab 0a fd 4c 89 f7 be 03
RSP: 0018:ffffc90000d47d10 EFLAGS: 00010293
RAX: ffffffff845f3077 RBX: ffff8881011d9000 RCX: ffff88810dfebc00
RDX: 0000000000000000 RSI: 0000000011ed3330 RDI: 000000000c04eb7d
RBP: ffffc90000d47d30 R08: ffff8881011d9083 R09: 1ffff1102023b210
R10: dffffc0000000000 R11: ffffed102023b211 R12: dffffc0000000000
R13: dffffc0000000000 R14: 0000000011ed3330 R15: ffff888129ede000
FS:  00007f092660b6c0(0000) GS:ffff8881f7000000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000001b34023ffc CR3: 000000011b398000 CR4: 00000000003506b0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 pppol2tp_release+0x150/0x2b0 net/l2tp/l2tp_ppp.c:435
 __sock_release net/socket.c:649 [inline]
 sock_close+0xb8/0x200 net/socket.c:1336
 __fput+0x22b/0x900 fs/file_table.c:311
 ____fput+0x15/0x20 fs/file_table.c:339
 task_work_run+0x127/0x190 kernel/task_work.c:188
 tracehook_notify_signal include/linux/tracehook.h:214 [inline]
 handle_signal_work kernel/entry/common.c:155 [inline]
 exit_to_user_mode_loop+0x96/0xe0 kernel/entry/common.c:181
 exit_to_user_mode_prepare+0x87/0xd0 kernel/entry/common.c:217
 __syscall_exit_to_user_mode_work kernel/entry/common.c:299 [inline]
 syscall_exit_to_user_mode+0x1a/0x30 kernel/entry/common.c:310
 do_syscall_64+0x58/0xa0 arch/x86/entry/common.c:86
 entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7f0927bb22d9
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:00007f092660b028 EFLAGS: 00000246 ORIG_RAX: 0000000000000133
RAX: 0000000000000245 RBX: 00007f0927e39fa0 RCX: 00007f0927bb22d9
RDX: 0000000000034000 RSI: 0000200000004380 RDI: 0000000000000004
RBP: 00007f0927c49888 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f0927e3a038 R14: 00007f0927e39fa0 R15: 00007fffe688edf8
 </TASK>
---[ end trace 7d3744080dca6df4 ]---

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/10/14 07:14 android13-5.15-lts 5ca734335a87 7321cd29 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-15 KASAN: use-after-free Read in l2tp_xmit_skb
* Struck through repros no longer work on HEAD.