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KASAN: use-after-free Read in tcp_write_timer_handler (2)

Status: upstream: reported on 2026/01/05 20:49
Reported-by: syzbot+8b2b7809c34e65a99a5b@syzkaller.appspotmail.com
First crash: 55d, last: 8d20h
▶ ▼ Similar bugs (9)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
linux-4.14 KASAN: use-after-free Read in tcp_write_timer_handler 19 1 2264d 2264d 0/1 auto-closed as invalid on 2020/04/17 21:22
upstream KASAN: use-after-free Read in tcp_write_timer_handler net 19 6 2542d 2606d 0/29 closed as invalid on 2019/04/19 22:15
linux-4.19 KASAN: use-after-free Read in tcp_write_timer_handler 19 1 1957d 1957d 0/1 auto-closed as invalid on 2021/02/18 23:19
upstream KASAN: use-after-free Read in tcp_write_timer_handler (2) net 19 5 2504d 2506d 0/29 closed as invalid on 2019/05/15 23:07
upstream KASAN: use-after-free Read in tcp_write_timer_handler (3) net 19 82 2356d 2418d 0/29 auto-closed as invalid on 2019/12/04 07:54
linux-5.15 KASAN: use-after-free Read in tcp_write_timer_handler origin:upstream 19 C error 234 566d 1088d 0/3 auto-obsoleted due to no activity on 2024/10/22 01:47
linux-6.1 KASAN: use-after-free Read in tcp_write_timer_handler 19 140 663d 1089d 0/3 auto-obsoleted due to no activity on 2024/07/16 13:06
linux-4.19 KASAN: use-after-free Read in tcp_write_timer_handler (2) 19 12 1251d 1766d 0/1 auto-obsoleted due to no activity on 2023/01/25 19:39
upstream KASAN: use-after-free Read in tcp_write_timer_handler (4) net 19 529 1174d 2200d 0/29 closed as invalid on 2023/03/21 22:54

Sample crash report:
==================================================================
BUG: KASAN: use-after-free in tcp_probe_timer net/ipv4/tcp_timer.c:380 [inline]
BUG: KASAN: use-after-free in tcp_write_timer_handler+0x876/0x9a0 net/ipv4/tcp_timer.c:659
Read of size 1 at addr ffff888075805615 by task syz.8.5543/24386

CPU: 1 PID: 24386 Comm: syz.8.5543 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
Call Trace:
 <IRQ>
 dump_stack_lvl+0x188/0x250 lib/dump_stack.c:106
 print_address_description+0x60/0x2d0 mm/kasan/report.c:248
 __kasan_report mm/kasan/report.c:434 [inline]
 kasan_report+0xdf/0x130 mm/kasan/report.c:451
 tcp_probe_timer net/ipv4/tcp_timer.c:380 [inline]
 tcp_write_timer_handler+0x876/0x9a0 net/ipv4/tcp_timer.c:659
 tcp_write_timer+0x126/0x280 net/ipv4/tcp_timer.c:675
 call_timer_fn+0x17b/0x540 kernel/time/timer.c:1648
 expire_timers kernel/time/timer.c:1699 [inline]
 __run_timers+0x53e/0x800 kernel/time/timer.c:1970
 run_timer_softirq+0x63/0xf0 kernel/time/timer.c:1983
 handle_softirqs+0x339/0x830 kernel/softirq.c:576
 __do_softirq kernel/softirq.c:610 [inline]
 invoke_softirq kernel/softirq.c:450 [inline]
 __irq_exit_rcu+0x13b/0x230 kernel/softirq.c:659
 irq_exit_rcu+0x5/0x20 kernel/softirq.c:671
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1108 [inline]
 sysvec_apic_timer_interrupt+0xa0/0xc0 arch/x86/kernel/apic/apic.c:1108
 </IRQ>
 <TASK>
 asm_sysvec_apic_timer_interrupt+0x16/0x20 arch/x86/include/asm/idtentry.h:676
RIP: 0010:native_save_fl arch/x86/include/asm/irqflags.h:29 [inline]
RIP: 0010:arch_local_save_flags arch/x86/include/asm/irqflags.h:70 [inline]
RIP: 0010:arch_local_irq_save arch/x86/include/asm/irqflags.h:106 [inline]
RIP: 0010:lock_is_held_type+0x61/0x190 kernel/locking/lockdep.c:5662
Code: 0f 85 f4 00 00 00 65 48 8b 1d 4b 44 46 76 83 bb ec 0a 00 00 00 0f 85 df 00 00 00 41 89 f7 49 89 fe 48 c7 04 24 00 00 00 00 9c <8f> 04 24 4c 8b 2c 24 fa 48 c7 c7 80 35 2b 8a e8 4b 0e 00 00 65 ff
RSP: 0018:ffffc9000308f770 EFLAGS: 00000246
RAX: 0000000000000000 RBX: ffff88801e0ed940 RCX: 4b32dc2084947800
RDX: ffffc90006181000 RSI: 00000000ffffffff RDI: ffffffff8c31eaa0
RBP: 00000000ffffffff R08: dffffc0000000000 R09: 1ffffffff203a618
R10: dffffc0000000000 R11: fffffbfff203a619 R12: dffffc0000000000
R13: 1ffff92000611efc R14: ffffffff8c31eaa0 R15: 00000000ffffffff
 task_css include/linux/cgroup.h:496 [inline]
 mem_cgroup_from_task+0x96/0x110 mm/memcontrol.c:935
 count_memcg_event_mm+0x164/0x370 include/linux/memcontrol.h:1080
 handle_mm_fault+0x134/0x4410 mm/memory.c:4863
 do_user_addr_fault+0x489/0xc80 arch/x86/mm/fault.c:1355
 handle_page_fault arch/x86/mm/fault.c:1443 [inline]
 exc_page_fault+0x60/0x100 arch/x86/mm/fault.c:1496
 asm_exc_page_fault+0x22/0x30 arch/x86/include/asm/idtentry.h:606
RIP: 0010:copy_user_enhanced_fast_string+0xe/0x40 arch/x86/lib/copy_user_64.S:206
Code: 89 d1 c1 e9 03 83 e2 07 f3 48 a5 89 d1 f3 a4 31 c0 0f 01 ca c3 90 90 90 90 90 90 90 0f 01 cb 83 fa 40 0f 82 70 ff ff ff 89 d1 <f3> a4 31 c0 0f 01 ca c3 90 90 90 90 90 90 90 90 90 90 89 d1 83 f8
RSP: 0018:ffffc9000308fbe0 EFLAGS: 00050206
RAX: ffffffff83e3cf01 RBX: 000000000000ffd0 RCX: 00000000000011f0
RDX: 000000000000ffd0 RSI: 000020000012f000 RDI: ffff88802f80ede0
RBP: 0000000000000000 R08: ffff88802f80ffcf R09: 1ffff11005f01ff9
R10: dffffc0000000000 R11: ffffed1005f01ffa R12: 00007ffffffff000
R13: 00002000001301f0 R14: ffff88802f800000 R15: 0000200000120220
 copy_user_generic arch/x86/include/asm/uaccess_64.h:37 [inline]
 raw_copy_from_user arch/x86/include/asm/uaccess_64.h:52 [inline]
 _copy_from_user+0xfa/0x170 lib/usercopy.c:23
 copy_from_user include/linux/uaccess.h:192 [inline]
 generic_map_update_batch+0x4d5/0x7d0 kernel/bpf/syscall.c:1427
 bpf_map_do_batch+0x466/0x600 kernel/bpf/syscall.c:-1
 __sys_bpf+0x671/0x6f0 kernel/bpf/syscall.c:-1
 __do_sys_bpf kernel/bpf/syscall.c:4761 [inline]
 __se_sys_bpf kernel/bpf/syscall.c:4759 [inline]
 __x64_sys_bpf+0x78/0x90 kernel/bpf/syscall.c:4759
 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: 0033:0x7fa64d9d7629
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:00007fa64bc31028 EFLAGS: 00000246 ORIG_RAX: 0000000000000141
RAX: ffffffffffffffda RBX: 00007fa64dc50fa0 RCX: 00007fa64d9d7629
RDX: 0000000000000038 RSI: 0000200000000200 RDI: 000000000000001a
RBP: 00007fa64da6db39 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fa64dc51038 R14: 00007fa64dc50fa0 R15: 00007fff374618f8
 </TASK>

Allocated by task 13337:
 kasan_save_stack mm/kasan/common.c:38 [inline]
 kasan_set_track mm/kasan/common.c:46 [inline]
 set_alloc_info mm/kasan/common.c:434 [inline]
 __kasan_slab_alloc+0x9c/0xd0 mm/kasan/common.c:467
 kasan_slab_alloc include/linux/kasan.h:254 [inline]
 slab_post_alloc_hook+0x4c/0x380 mm/slab.h:519
 slab_alloc_node mm/slub.c:3225 [inline]
 slab_alloc mm/slub.c:3233 [inline]
 kmem_cache_alloc+0x100/0x290 mm/slub.c:3238
 kmem_cache_zalloc include/linux/slab.h:728 [inline]
 net_alloc net/core/net_namespace.c:418 [inline]
 copy_net_ns+0x13c/0x5b0 net/core/net_namespace.c:490
 create_new_namespaces+0x3d3/0x6f0 kernel/nsproxy.c:110
 unshare_nsproxy_namespaces+0x116/0x160 kernel/nsproxy.c:226
 ksys_unshare+0x4ca/0x8b0 kernel/fork.c:3175
 __do_sys_unshare kernel/fork.c:3249 [inline]
 __se_sys_unshare kernel/fork.c:3247 [inline]
 __x64_sys_unshare+0x34/0x40 kernel/fork.c:3247
 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 ffff888075804f80
 which belongs to the cache net_namespace of size 6528
The buggy address is located 1685 bytes inside of
 6528-byte region [ffff888075804f80, ffff888075806900)
The buggy address belongs to the page:
page:ffffea0001d60000 refcount:1 mapcount:0 mapping:0000000000000000 index:0xffff888075800000 pfn:0x75800
head:ffffea0001d60000 order:3 compound_mapcount:0 compound_pincount:0
memcg:ffff88802571a301
flags: 0xfff00000010200(slab|head|node=0|zone=1|lastcpupid=0x7ff)
raw: 00fff00000010200 ffffea0001d6ca00 0000000200000002 ffff888016de93c0
raw: ffff888075800000 0000000080040002 00000001ffffffff ffff88802571a301
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 3, migratetype Unmovable, gfp_mask 0x1d20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC|__GFP_HARDWALL), pid 9630, ts 210014096223, free_ts 209952310426
 prep_new_page mm/page_alloc.c:2426 [inline]
 get_page_from_freelist+0x1bbd/0x1ca0 mm/page_alloc.c:4192
 __alloc_pages+0x1ee/0x480 mm/page_alloc.c:5487
 alloc_slab_page mm/slub.c:1780 [inline]
 allocate_slab mm/slub.c:1917 [inline]
 new_slab+0xc0/0x4b0 mm/slub.c:1980
 ___slab_alloc+0x80a/0xdd0 mm/slub.c:3013
 __slab_alloc mm/slub.c:3100 [inline]
 slab_alloc_node mm/slub.c:3191 [inline]
 slab_alloc mm/slub.c:3233 [inline]
 kmem_cache_alloc+0x195/0x290 mm/slub.c:3238
 kmem_cache_zalloc include/linux/slab.h:728 [inline]
 net_alloc net/core/net_namespace.c:418 [inline]
 copy_net_ns+0x13c/0x5b0 net/core/net_namespace.c:490
 create_new_namespaces+0x3d3/0x6f0 kernel/nsproxy.c:110
 copy_namespaces+0x37d/0x3e0 kernel/nsproxy.c:178
 copy_process+0x1834/0x3e20 kernel/fork.c:2293
 kernel_clone+0x23f/0x990 kernel/fork.c:2679
 __do_sys_clone kernel/fork.c:2796 [inline]
 __se_sys_clone kernel/fork.c:2780 [inline]
 __x64_sys_clone+0x19a/0x210 kernel/fork.c:2780
 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
page last free stack trace:
 reset_page_owner include/linux/page_owner.h:24 [inline]
 free_pages_prepare mm/page_alloc.c:1340 [inline]
 free_pcp_prepare mm/page_alloc.c:1391 [inline]
 free_unref_page_prepare+0x637/0x6c0 mm/page_alloc.c:3317
 free_unref_page+0x8f/0x2a0 mm/page_alloc.c:3396
 qlist_free_all+0x35/0x90 mm/kasan/quarantine.c:176
 kasan_quarantine_reduce+0x150/0x160 mm/kasan/quarantine.c:283
 __kasan_slab_alloc+0x2f/0xd0 mm/kasan/common.c:444
 kasan_slab_alloc include/linux/kasan.h:254 [inline]
 slab_post_alloc_hook+0x4c/0x380 mm/slab.h:519
 slab_alloc_node mm/slub.c:3225 [inline]
 slab_alloc mm/slub.c:3233 [inline]
 kmem_cache_alloc+0x100/0x290 mm/slub.c:3238
 __d_alloc+0x2a/0x6f0 fs/dcache.c:1749
 d_alloc_pseudo+0x19/0x70 fs/dcache.c:1880
 alloc_file_pseudo+0xe0/0x200 fs/file_table.c:256
 __anon_inode_getfile fs/anon_inodes.c:109 [inline]
 __anon_inode_getfd+0x26b/0x3d0 fs/anon_inodes.c:165
 __btf_new_fd kernel/bpf/btf.c:5912 [inline]
 btf_new_fd+0x779/0x910 kernel/bpf/btf.c:5939
 __sys_bpf+0x58c/0x6f0 kernel/bpf/syscall.c:4702
 __do_sys_bpf kernel/bpf/syscall.c:4761 [inline]
 __se_sys_bpf kernel/bpf/syscall.c:4759 [inline]
 __x64_sys_bpf+0x78/0x90 kernel/bpf/syscall.c:4759
 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

Memory state around the buggy address:
 ffff888075805500: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff888075805580: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff888075805600: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                         ^
 ffff888075805680: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff888075805700: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================
----------------
Code disassembly (best guess):
   0:	0f 85 f4 00 00 00    	jne    0xfa
   6:	65 48 8b 1d 4b 44 46 	mov    %gs:0x7646444b(%rip),%rbx        # 0x76464459
   d:	76
   e:	83 bb ec 0a 00 00 00 	cmpl   $0x0,0xaec(%rbx)
  15:	0f 85 df 00 00 00    	jne    0xfa
  1b:	41 89 f7             	mov    %esi,%r15d
  1e:	49 89 fe             	mov    %rdi,%r14
  21:	48 c7 04 24 00 00 00 	movq   $0x0,(%rsp)
  28:	00
  29:	9c                   	pushf
* 2a:	8f 04 24             	pop    (%rsp) <-- trapping instruction
  2d:	4c 8b 2c 24          	mov    (%rsp),%r13
  31:	fa                   	cli
  32:	48 c7 c7 80 35 2b 8a 	mov    $0xffffffff8a2b3580,%rdi
  39:	e8 4b 0e 00 00       	call   0xe89
  3e:	65                   	gs
  3f:	ff                   	.byte 0xff

Crashes (2):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/02/21 07:08 linux-5.15.y 3330a8d33e08 6e7b5511 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf KASAN: use-after-free Read in tcp_write_timer_handler
2026/01/05 20:48 linux-5.15.y 68efe5a6c16a d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf KASAN: use-after-free Read in tcp_write_timer_handler
* Struck through repros no longer work on HEAD.