KASAN: use-after-free Read in check_tty_count

Status: upstream: reported C repro on 2026/08/10 02:57
Reported-by: syzbot+90ffe1583ffe9c58c485@syzkaller.appspotmail.com
First crash: 56d, last: 8d09h
▶ ▼ Similar bugs (4)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
android-5-15 KASAN: use-after-free Read in check_tty_count 19 syz, C 3 23d 53d 0/2 upstream: reported C repro on 2026/08/13 03:54
android-6-1 KASAN: use-after-free Read in check_tty_count origin:upstream 19 syz, C 4 15d 56d 0/2 upstream: reported C repro on 2026/08/10 10:56
upstream KASAN: slab-use-after-free Read in check_tty_count prio:normal serial 19 syz, C error 4 4d15h 49d 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 26d 55d 0/1 premoderation: reported C repro on 2026/08/11 15:00
▶ ▼ Fix bisection attempts (1)
Created Duration User Patch Repo Result
2026/09/27 11:54 1h57m bisect fix android13-5.10-lts OK (0) 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.h:616 [inline]
BUG: KASAN: use-after-free in check_tty_count+0x1a8/0x330 drivers/tty/tty_io.c:295
Read of size 8 at addr ffff888107593110 by task syz-executor780/305

CPU: 1 PID: 305 Comm: syz-executor780 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
Call Trace:
 __dump_stack+0x21/0x24 lib/dump_stack.c:77
 dump_stack_lvl+0x1a7/0x208 lib/dump_stack.c:118
 print_address_description+0x7f/0x2c0 mm/kasan/report.c:248
 __kasan_report mm/kasan/report.c:435 [inline]
 kasan_report+0x100/0x140 mm/kasan/report.c:452
 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.h:616 [inline]
 check_tty_count+0x1a8/0x330 drivers/tty/tty_io.c:295
 tty_release+0xc9/0x1330 drivers/tty/tty_io.c:1747
 __fput+0x2dc/0x730 fs/file_table.c:281
 ____fput+0x15/0x20 fs/file_table.c:314
 task_work_run+0x127/0x190 kernel/task_work.c:189
 exit_task_work include/linux/task_work.h:33 [inline]
 do_exit+0xa7c/0x24e0 kernel/exit.c:873
 do_group_exit+0x149/0x310 kernel/exit.c:987
 __do_sys_exit_group kernel/exit.c:998 [inline]
 __se_sys_exit_group kernel/exit.c:996 [inline]
 __x64_sys_exit_group+0x3f/0x40 kernel/exit.c:996
 do_syscall_64+0x31/0x40 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x61/0xcb
RIP: 0033:0x7fce6da24745
Code: Unable to access opcode bytes at RIP 0x7fce6da2471b.
RSP: 002b:00007ffd603230a8 EFLAGS: 00000202 ORIG_RAX: 00000000000000e7
RAX: ffffffffffffffda RBX: 0000000000000001 RCX: 00007fce6da24745
RDX: 00000000000000e7 RSI: ffffffffffffffd0 RDI: 0000000000000000
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000202 R12: 0000000000000000
R13: 00007fce6dad5120 R14: 00007fce6dad74e8 R15: 00007fce6dad7500

Allocated by task 307:
 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:430 [inline]
 ____kasan_kmalloc mm/kasan/common.c:509 [inline]
 __kasan_kmalloc+0xd4/0x100 mm/kasan/common.c:518
 kasan_kmalloc include/linux/kasan.h:254 [inline]
 kmem_cache_alloc_trace+0x179/0x2e0 mm/slub.c:2979
 kmalloc include/linux/slab.h:555 [inline]
 kzalloc include/linux/slab.h:667 [inline]
 gs_port_alloc drivers/usb/gadget/function/u_serial.c:1162 [inline]
 gserial_alloc_line_no_console+0x238/0x700 drivers/usb/gadget/function/u_serial.c:1242
 gserial_alloc_line+0x15/0x20 drivers/usb/gadget/function/u_serial.c:1276
 acm_alloc_instance+0x86/0xe0 drivers/usb/gadget/function/f_acm.c:849
 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:636
 configfs_mkdir+0x5d2/0xd90 fs/configfs/dir.c:1354
 vfs_mkdir+0x42c/0x600 fs/namei.c:3798
 do_mkdirat+0x14c/0x340 fs/namei.c:3820
 __do_sys_mkdirat fs/namei.c:3831 [inline]
 __se_sys_mkdirat fs/namei.c:3829 [inline]
 __x64_sys_mkdirat+0x7b/0x90 fs/namei.c:3829
 do_syscall_64+0x31/0x40 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x61/0xcb

Freed by task 307:
 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:362
 __kasan_slab_free+0x11/0x20 mm/kasan/common.c:370
 kasan_slab_free include/linux/kasan.h:220 [inline]
 slab_free_hook mm/slub.c:1600 [inline]
 slab_free_freelist_hook+0xc5/0x190 mm/slub.c:1626
 slab_free mm/slub.c:3208 [inline]
 kfree+0xc0/0x270 mm/slub.c:4196
 gserial_free_port+0x240/0x2d0 drivers/usb/gadget/function/u_serial.c:1206
 gserial_free_line+0x9f/0x1b0 drivers/usb/gadget/function/u_serial.c:1223
 acm_free_instance+0x39/0x60 drivers/usb/gadget/function/f_acm.c:836
 usb_put_function_instance+0x85/0xa0 drivers/usb/gadget/functions.c:77
 acm_attr_release+0x15/0x20 drivers/usb/gadget/function/f_acm.c:785
 config_item_cleanup fs/configfs/item.c:130 [inline]
 config_item_release fs/configfs/item.c:139 [inline]
 kref_put include/linux/kref.h:65 [inline]
 config_item_put+0x158/0x210 fs/configfs/item.c:151
 configfs_rmdir+0x89f/0x960 fs/configfs/dir.c:1580
 vfs_rmdir+0x1ab/0x3c0 fs/namei.c:3860
 do_rmdir+0x232/0x630 fs/namei.c:3920
 __do_sys_rmdir fs/namei.c:3938 [inline]
 __se_sys_rmdir fs/namei.c:3936 [inline]
 __x64_sys_rmdir+0x49/0x50 fs/namei.c:3936
 do_syscall_64+0x31/0x40 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x61/0xcb

The buggy address belongs to the object at ffff888107593000
 which belongs to the cache kmalloc-1k of size 1024
The buggy address is located 272 bytes inside of
 1024-byte region [ffff888107593000, ffff888107593400)
The buggy address belongs to the page:
page:ffffea00041d6400 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x107590
head:ffffea00041d6400 order:3 compound_mapcount:0 compound_pincount:0
flags: 0x4000000000010200(slab|head)
raw: 4000000000010200 dead000000000100 dead000000000122 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 3, migratetype Unmovable, gfp_mask 0xd2a20(GFP_ATOMIC|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 295, ts 25177018857, free_ts 25175064365
 set_page_owner include/linux/page_owner.h:35 [inline]
 post_alloc_hook mm/page_alloc.c:2456 [inline]
 prep_new_page+0x176/0x190 mm/page_alloc.c:2462
 get_page_from_freelist+0x225f/0x23f0 mm/page_alloc.c:4254
 __alloc_pages_nodemask+0x29a/0x640 mm/page_alloc.c:5384
 alloc_slab_page mm/slub.c:-1 [inline]
 allocate_slab mm/slub.c:1813 [inline]
 new_slab+0x84/0x3f0 mm/slub.c:1874
 new_slab_objects mm/slub.c:2632 [inline]
 ___slab_alloc+0x2f8/0x4c0 mm/slub.c:2796
 __slab_alloc+0x63/0xa0 mm/slub.c:2836
 slab_alloc_node mm/slub.c:2918 [inline]
 slab_alloc mm/slub.c:2960 [inline]
 __kmalloc_track_caller+0x1e4/0x310 mm/slub.c:4541
 __kmalloc_reserve net/core/skbuff.c:144 [inline]
 __alloc_skb+0xdc/0x520 net/core/skbuff.c:212
 __napi_alloc_skb+0x158/0x2e0 net/core/skbuff.c:522
 napi_alloc_skb include/linux/skbuff.h:2975 [inline]
 page_to_skb+0x40/0x930 drivers/net/virtio_net.c:432
 receive_mergeable drivers/net/virtio_net.c:1049 [inline]
 receive_buf+0xc03/0x46a0 drivers/net/virtio_net.c:1159
 virtnet_receive drivers/net/virtio_net.c:1451 [inline]
 virtnet_poll+0x3c9/0xef0 drivers/net/virtio_net.c:1560
 napi_poll net/core/dev.c:6885 [inline]
 net_rx_action+0x48d/0xed0 net/core/dev.c:6955
 __do_softirq+0x255/0x563 kernel/softirq.c:309
page last free stack trace:
 reset_page_owner include/linux/page_owner.h:28 [inline]
 free_pages_prepare mm/page_alloc.c:1349 [inline]
 __free_pages_ok+0x80b/0x830 mm/page_alloc.c:1629
 free_compound_page+0x73/0x90 mm/page_alloc.c:710
 destroy_compound_page include/linux/mm.h:970 [inline]
 __put_compound_page+0x77/0xb0 mm/swap.c:117
 __put_page+0xbd/0xe0 mm/swap.c:133
 put_page include/linux/mm.h:1268 [inline]
 page_to_skb+0x3d9/0x930 drivers/net/virtio_net.c:473
 receive_mergeable drivers/net/virtio_net.c:1049 [inline]
 receive_buf+0xc03/0x46a0 drivers/net/virtio_net.c:1159
 virtnet_receive drivers/net/virtio_net.c:1451 [inline]
 virtnet_poll+0x3c9/0xef0 drivers/net/virtio_net.c:1560
 napi_poll net/core/dev.c:6885 [inline]
 net_rx_action+0x48d/0xed0 net/core/dev.c:6955
 __do_softirq+0x255/0x563 kernel/softirq.c:309

Memory state around the buggy address:
 ffff888107593000: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff888107593080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff888107593100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                         ^
 ffff888107593180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff888107593200: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================
------------[ cut here ]------------
WARNING: CPU: 0 PID: 305 at drivers/usb/gadget/function/u_serial.c:690 gs_close+0x17d/0x9a0 drivers/usb/gadget/function/u_serial.c:690
Modules linked in:
CPU: 0 PID: 305 Comm: syz-executor780 Tainted: G    B             syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
RIP: 0010:gs_close+0x17d/0x9a0 drivers/usb/gadget/function/u_serial.c:690
Code: 7c 56 fe 41 ff cc 42 0f b6 04 2b 84 c0 0f 85 c1 06 00 00 48 8b 44 24 20 44 89 20 48 8b 5c 24 38 e9 bd 02 00 00 e8 83 7c 56 fe <0f> 0b 48 8b 5c 24 38 e9 ac 02 00 00 e8 72 7c 56 fe 49 8d bf 90 02
RSP: 0018:ffffc9000095fac0 EFLAGS: 00010093
RAX: ffffffff830e295d RBX: 1ffff11020eb261a RCX: ffff888122113b40
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: ffffc9000095fbd8 R08: 0000000000000003 R09: 0000000000000004
R10: dffffc0000000000 R11: fffff5200012bf48 R12: 0000000000000000
R13: dffffc0000000000 R14: 1ffff9200012bf60 R15: ffff888107593000
FS:  0000000000000000(0000) GS:ffff8881f7000000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fce6da77da0 CR3: 0000000105be7000 CR4: 00000000003506b0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 tty_release+0x3c8/0x1330 drivers/tty/tty_io.c:1764
 __fput+0x2dc/0x730 fs/file_table.c:281
 ____fput+0x15/0x20 fs/file_table.c:314
 task_work_run+0x127/0x190 kernel/task_work.c:189
 exit_task_work include/linux/task_work.h:33 [inline]
 do_exit+0xa7c/0x24e0 kernel/exit.c:873
 do_group_exit+0x149/0x310 kernel/exit.c:987
 __do_sys_exit_group kernel/exit.c:998 [inline]
 __se_sys_exit_group kernel/exit.c:996 [inline]
 __x64_sys_exit_group+0x3f/0x40 kernel/exit.c:996
 do_syscall_64+0x31/0x40 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x61/0xcb
RIP: 0033:0x7fce6da24745
Code: Unable to access opcode bytes at RIP 0x7fce6da2471b.
RSP: 002b:00007ffd603230a8 EFLAGS: 00000202 ORIG_RAX: 00000000000000e7
RAX: ffffffffffffffda RBX: 0000000000000001 RCX: 00007fce6da24745
RDX: 00000000000000e7 RSI: ffffffffffffffd0 RDI: 0000000000000000
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000202 R12: 0000000000000000
R13: 00007fce6dad5120 R14: 00007fce6dad74e8 R15: 00007fce6dad7500
---[ end trace 857023a59222e9c6 ]---

Crashes (3):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/08/10 02:52 android13-5.10-lts 447db0046f21 5d63f80b .config strace log report syz / log C [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in check_tty_count
2026/08/20 01:50 android13-5.10-lts e334a66065d3 1e72964b .config strace log report syz / log [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in check_tty_count
2026/08/10 01:58 android13-5.10-lts 447db0046f21 5d63f80b .config strace log report syz / log [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in check_tty_count
* Struck through repros no longer work on HEAD.