KASAN: use-after-free Read in check_tty_count

Status: upstream: reported C repro on 2026/08/13 03:54
Bug presence: origin:upstream
[Documentation on labels]
Reported-by: syzbot+bdf7edb71630a4a328b0@syzkaller.appspotmail.com
First crash: 66d, last: 35d
▶ ▼ Bug presence (2)
Date Name Commit Repro Result
2026/10/13 lts (merge base) 722980f27458 C [report] KASAN: use-after-free Read in check_tty_count
2026/10/13 upstream (ToT) 24a19b953e2a C [report] KASAN: slab-use-after-free Read in check_tty_count
▶ ▼ Similar bugs (4)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
android-6-1 KASAN: use-after-free Read in check_tty_count origin:upstream 19 syz, C 4 28d 69d 0/2 upstream: reported C repro on 2026/08/10 10:56
android-5-10 KASAN: use-after-free Read in check_tty_count 19 syz, C 3 1d11h 69d 0/2 upstream: reported C repro on 2026/08/10 02:57
upstream KASAN: slab-use-after-free Read in check_tty_count prio:normal serial 19 syz, C error 4 17d 62d 0/29 upstream: reported C repro on 2026/08/17 13:05
android-6-12 KASAN: slab-use-after-free Read in check_tty_count origin:upstream 19 syz, C 4 38d 67d 0/1 premoderation: reported C repro on 2026/08/11 15:00
▶ ▼ Last patch testing requests (3)
Created Duration User Patch Repo Result
2026/09/12 14:47 15m retest repro android13-5.15-lts report job log log
2026/09/12 14:47 9m retest repro android13-5.15-lts report job log log
2026/09/12 14:47 13m retest repro android13-5.15-lts report job log log

Sample crash report:
==================================================================
BUG: KASAN: use-after-free in instrument_atomic_read include/linux/instrumented.h:71 [inline]
BUG: KASAN: use-after-free in test_bit include/asm-generic/bitops/instrumented-non-atomic.h:134 [inline]
BUG: KASAN: use-after-free in tty_port_kopened include/linux/tty_port.h:180 [inline]
BUG: KASAN: use-after-free in check_tty_count+0x1a8/0x330 drivers/tty/tty_io.c:294
Read of size 8 at addr ffff88810dc43910 by task syz-executor950/316

CPU: 1 PID: 316 Comm: syz-executor950 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
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
 check_region_inline mm/kasan/generic.c:-1 [inline]
 kasan_check_range+0x249/0x2a0 mm/kasan/generic.c:189
 __kasan_check_read+0x11/0x20 mm/kasan/shadow.c:31
 instrument_atomic_read include/linux/instrumented.h:71 [inline]
 test_bit include/asm-generic/bitops/instrumented-non-atomic.h:134 [inline]
 tty_port_kopened include/linux/tty_port.h:180 [inline]
 check_tty_count+0x1a8/0x330 drivers/tty/tty_io.c:294
 tty_release+0xc9/0x1330 drivers/tty/tty_io.c:1756
 __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
 ptrace_notify+0x230/0x270 kernel/signal.c:2392
 ptrace_report_syscall include/linux/tracehook.h:66 [inline]
 tracehook_report_syscall_exit include/linux/tracehook.h:130 [inline]
 arch_syscall_exit_tracehook include/linux/entry-common.h:297 [inline]
 syscall_exit_work+0x87/0x160 kernel/entry/common.c:262
 syscall_exit_to_user_mode_prepare+0x1c/0x20 kernel/entry/common.c:289
 __syscall_exit_to_user_mode_work kernel/entry/common.c:294 [inline]
 syscall_exit_to_user_mode+0xd/0x30 kernel/entry/common.c:307
 do_syscall_64+0x58/0xa0 arch/x86/entry/common.c:86
 entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7fb883e9037e
Code: 08 0f 85 05 e3 ff ff 49 89 fb 48 89 f0 48 89 d7 48 89 ce 4c 89 c2 4d 89 ca 4c 8b 44 24 08 4c 8b 4c 24 10 4c 89 5c 24 08 0f 05 <c3> 90 41 57 41 56 4d 89 c6 41 55 4d 89 cd 41 54 55 53 48 83 ec 08
RSP: 002b:00007ffdf1260df8 EFLAGS: 00000246 ORIG_RAX: 0000000000000003
RAX: 0000000000000000 RBX: 0000555568c7a3c0 RCX: 00007fb883e9037e
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000003
RBP: 00007ffdf1260e80 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007fb883f15b4c
R13: 000000000000bac2 R14: 00007ffdf1260ea0 R15: 00007fb883e4d690
 </TASK>

Allocated by task 319:
 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]
 kmem_cache_alloc_trace+0x119/0x270 mm/slub.c:3274
 kmalloc include/linux/slab.h:619 [inline]
 kzalloc include/linux/slab.h:750 [inline]
 gs_port_alloc drivers/usb/gadget/function/u_serial.c:1158 [inline]
 gserial_alloc_line_no_console+0x238/0x700 drivers/usb/gadget/function/u_serial.c:1238
 obex_alloc_inst+0x86/0xe0 drivers/usb/gadget/function/f_obex.c:435
 try_get_usb_function_instance drivers/usb/gadget/functions.c:28 [inline]
 usb_get_function_instance+0xe2/0x2f0 drivers/usb/gadget/functions.c:44
 function_make+0x118/0x350 drivers/usb/gadget/configfs.c:642
 configfs_mkdir+0x50a/0x9c0 fs/configfs/dir.c:1329
 vfs_mkdir+0x38b/0x590 fs/namei.c:4073
 do_mkdirat+0x174/0x4d0 fs/namei.c:4098
 __do_sys_mkdirat fs/namei.c:4113 [inline]
 __se_sys_mkdirat fs/namei.c:4111 [inline]
 __x64_sys_mkdirat+0x89/0xa0 fs/namei.c:4111
 x64_sys_call+0x37e/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:259
 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 321:
 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
 gserial_free_port+0x245/0x2e0 drivers/usb/gadget/function/u_serial.c:1202
 gserial_free_line+0x9b/0x1a0 drivers/usb/gadget/function/u_serial.c:1219
 obex_free_inst+0x39/0x60 drivers/usb/gadget/function/f_obex.c:421
 usb_put_function_instance+0x85/0xa0 drivers/usb/gadget/functions.c:77
 obex_attr_release+0x15/0x20 drivers/usb/gadget/function/f_obex.c:391
 config_item_cleanup fs/configfs/item.c:128 [inline]
 config_item_release fs/configfs/item.c:137 [inline]
 kref_put include/linux/kref.h:65 [inline]
 config_item_put+0x158/0x210 fs/configfs/item.c:149
 configfs_rmdir+0x89f/0x960 fs/configfs/dir.c:1540
 vfs_rmdir+0x1ae/0x450 fs/namei.c:4157
 do_rmdir+0x261/0x6b0 fs/namei.c:4218
 __do_sys_rmdir fs/namei.c:4237 [inline]
 __se_sys_rmdir fs/namei.c:4235 [inline]
 __x64_sys_rmdir+0x49/0x50 fs/namei.c:4235
 x64_sys_call+0x25f/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:85
 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 ffff88810dc43800
 which belongs to the cache kmalloc-1k of size 1024
The buggy address is located 272 bytes inside of
 1024-byte region [ffff88810dc43800, ffff88810dc43c00)
The buggy address belongs to the page:
page:ffffea0004371000 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x10dc40
head:ffffea0004371000 order:3 compound_mapcount:0 compound_pincount:0
flags: 0x4000000000010200(slab|head|zone=1)
raw: 4000000000010200 0000000000000000 dead000000000122 ffff888100043080
raw: 0000000000000000 0000000000100010 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 3, migratetype Unmovable, gfp_mask 0xd20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 299, ts 47772114532, free_ts 47678805805
 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_fclone include/linux/skbuff.h:1233 [inline]
 sk_stream_alloc_skb+0x216/0xb70 net/ipv4/tcp.c:892
 tcp_sendmsg_locked+0xcbb/0x3330 net/ipv4/tcp.c:1317
 tcp_sendmsg+0x2f/0x50 net/ipv4/tcp.c:1460
 inet_sendmsg+0xa5/0xc0 net/ipv4/af_inet.c:830
 sock_sendmsg_nosec net/socket.c:704 [inline]
 __sock_sendmsg net/socket.c:716 [inline]
 sock_write_iter+0x2a6/0x3a0 net/socket.c:1080
 call_write_iter include/linux/fs.h:2212 [inline]
 new_sync_write fs/read_write.c:507 [inline]
 vfs_write+0x831/0xfd0 fs/read_write.c:594
 ksys_write+0x14a/0x260 fs/read_write.c:647
page last free stack trace:
 reset_page_owner include/linux/page_owner.h:26 [inline]
 free_pages_prepare mm/page_alloc.c:1474 [inline]
 free_pcp_prepare mm/page_alloc.c:1546 [inline]
 free_unref_page_prepare+0x5fa/0x600 mm/page_alloc.c:3536
 free_unref_page+0xae/0x540 mm/page_alloc.c:3618
 free_the_page mm/page_alloc.c:805 [inline]
 __free_pages+0x6c/0x100 mm/page_alloc.c:5900
 __free_slab+0xe5/0x1e0 mm/slub.c:2025
 free_slab mm/slub.c:2040 [inline]
 discard_slab mm/slub.c:2046 [inline]
 __unfreeze_partials+0x15a/0x190 mm/slub.c:2532
 put_cpu_partial+0xc6/0x120 mm/slub.c:2612
 __slab_free+0x1d4/0x290 mm/slub.c:3395
 do_slab_free mm/slub.c:3514 [inline]
 ___cache_free+0x104/0x120 mm/slub.c:3535
 qlink_free+0x4d/0x90 mm/kasan/quarantine.c:157
 qlist_free_all+0x5f/0xb0 mm/kasan/quarantine.c:176
 kasan_quarantine_reduce+0x14a/0x170 mm/kasan/quarantine.c:283
 __kasan_slab_alloc+0x2f/0xe0 mm/kasan/common.c:443
 kasan_slab_alloc include/linux/kasan.h:217 [inline]
 slab_post_alloc_hook+0x4f/0x2b0 mm/slab.h:550
 slab_alloc_node mm/slub.c:3245 [inline]
 slab_alloc mm/slub.c:3255 [inline]
 kmem_cache_alloc+0xf7/0x260 mm/slub.c:3260
 kmem_cache_zalloc include/linux/slab.h:740 [inline]
 alloc_vfsmnt+0x27/0x4a0 fs/namespace.c:208
 clone_mnt+0x6d/0xd00 fs/namespace.c:1067

Memory state around the buggy address:
 ffff88810dc43800: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88810dc43880: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff88810dc43900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                         ^
 ffff88810dc43980: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88810dc43a00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================
------------[ cut here ]------------
WARNING: CPU: 1 PID: 316 at drivers/usb/gadget/function/u_serial.c:686 gs_close+0x17d/0x9b0 drivers/usb/gadget/function/u_serial.c:686
Modules linked in:
CPU: 1 PID: 316 Comm: syz-executor950 Tainted: G    B             syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
RIP: 0010:gs_close+0x17d/0x9b0 drivers/usb/gadget/function/u_serial.c:686
Code: 83 3e fe 41 ff cc 42 0f b6 04 2b 84 c0 0f 85 c6 06 00 00 48 8b 44 24 20 44 89 20 48 8b 5c 24 38 e9 c2 02 00 00 e8 b3 83 3e fe <0f> 0b 48 8b 5c 24 38 e9 b1 02 00 00 e8 a2 83 3e fe 49 8d bf 90 02
RSP: 0018:ffffc90000ac7ae0 EFLAGS: 00010093
RAX: ffffffff832b33fd RBX: 1ffff11021b8871a RCX: ffff88810cb762c0
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: ffffc90000ac7be8 R08: 0000000000000003 R09: 0000000000000004
R10: dffffc0000000000 R11: fffff52000158f4c R12: 0000000000000000
R13: dffffc0000000000 R14: 1ffff92000158f64 R15: ffff88810dc43800
FS:  0000555568c7a3c0(0000) GS:ffff8881f7100000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fb883e90350 CR3: 000000010d7e8000 CR4: 00000000003506a0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 tty_release+0x3c8/0x1330 drivers/tty/tty_io.c:1773
 __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
 ptrace_notify+0x230/0x270 kernel/signal.c:2392
 ptrace_report_syscall include/linux/tracehook.h:66 [inline]
 tracehook_report_syscall_exit include/linux/tracehook.h:130 [inline]
 arch_syscall_exit_tracehook include/linux/entry-common.h:297 [inline]
 syscall_exit_work+0x87/0x160 kernel/entry/common.c:262
 syscall_exit_to_user_mode_prepare+0x1c/0x20 kernel/entry/common.c:289
 __syscall_exit_to_user_mode_work kernel/entry/common.c:294 [inline]
 syscall_exit_to_user_mode+0xd/0x30 kernel/entry/common.c:307
 do_syscall_64+0x58/0xa0 arch/x86/entry/common.c:86
 entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7fb883e9037e
Code: 08 0f 85 05 e3 ff ff 49 89 fb 48 89 f0 48 89 d7 48 89 ce 4c 89 c2 4d 89 ca 4c 8b 44 24 08 4c 8b 4c 24 10 4c 89 5c 24 08 0f 05 <c3> 90 41 57 41 56 4d 89 c6 41 55 4d 89 cd 41 54 55 53 48 83 ec 08
RSP: 002b:00007ffdf1260df8 EFLAGS: 00000246 ORIG_RAX: 0000000000000003
RAX: 0000000000000000 RBX: 0000555568c7a3c0 RCX: 00007fb883e9037e
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000003
RBP: 00007ffdf1260e80 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007fb883f15b4c
R13: 000000000000bac2 R14: 00007ffdf1260ea0 R15: 00007fb883e4d690
 </TASK>
---[ end trace 8ed7c3b6a9bf13f2 ]---

Crashes (3):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/08/27 22:36 android13-5.15-lts 54850912d011 69a01293 .config strace log report syz / log C [disk image] [vmlinux] [kernel image] ci2-android-5-15 KASAN: use-after-free Read in check_tty_count
2026/08/13 03:53 android13-5.15-lts 54275df9611d 359b2492 .config strace log report syz / log C [disk image] [vmlinux] [kernel image] ci2-android-5-15 KASAN: use-after-free Read in check_tty_count
2026/08/27 23:08 android13-5.15-lts 54850912d011 69a01293 .config strace log report syz / log [disk image] [vmlinux] [kernel image] ci2-android-5-15 KASAN: use-after-free Read in check_tty_count
* Struck through repros no longer work on HEAD.