KASAN: use-after-free Read in check_tty_count

Status: upstream: reported C repro on 2026/08/13 03:54
Reported-by: syzbot+bdf7edb71630a4a328b0@syzkaller.appspotmail.com
First crash: 1d16h, last: 1d16h
▶ ▼ Similar bugs (3)
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 19 syz, C 3 4d08h 4d09h 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 2 4d17h 4d17h 0/2 upstream: reported C repro on 2026/08/10 02:57
android-6-12 KASAN: slab-use-after-free Read in check_tty_count 19 syz 2 3d04h 3d05h 0/1 premoderation: reported syz repro on 2026/08/11 15:00

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 ffff888107bcd910 by task syz-executor637/314

CPU: 0 PID: 314 Comm: syz-executor637 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: 0033:0x7f25faf29bfe
Code: 08 0f 85 05 e2 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:00007ffeca1b1b48 EFLAGS: 00000246 ORIG_RAX: 0000000000000003
RAX: 0000000000000000 RBX: 000055555c9793c0 RCX: 00007f25faf29bfe
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000003
RBP: 00007ffeca1b1bd0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f25fafafb4c
R13: 00000000000089bd R14: 00007ffeca1b1bf0 R15: 00007f25faee8360
 </TASK>

Allocated by task 315:
 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
 gserial_alloc_line+0x15/0x20 drivers/usb/gadget/function/u_serial.c:1272
 acm_alloc_instance+0x86/0xe0 drivers/usb/gadget/function/f_acm.c:845
 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 315:
 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
 acm_free_instance+0x39/0x60 drivers/usb/gadget/function/f_acm.c:832
 usb_put_function_instance+0x85/0xa0 drivers/usb/gadget/functions.c:77
 acm_attr_release+0x15/0x20 drivers/usb/gadget/function/f_acm.c:781
 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 ffff888107bcd800
 which belongs to the cache kmalloc-1k of size 1024
The buggy address is located 272 bytes inside of
 1024-byte region [ffff888107bcd800, ffff888107bcdc00)
The buggy address belongs to the page:
page:ffffea00041ef200 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x107bc8
head:ffffea00041ef200 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 90, ts 35246911126, free_ts 26710585607
 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]
 alloc_skb_with_frags+0xa8/0x620 net/core/skbuff.c:6207
 sock_alloc_send_pskb+0x87f/0x9a0 net/core/sock.c:2542
 unix_dgram_sendmsg+0x6f3/0x19b0 net/unix/af_unix.c:1816
 sock_sendmsg_nosec net/socket.c:704 [inline]
 __sock_sendmsg net/socket.c:716 [inline]
 __sys_sendto+0x46d/0x620 net/socket.c:2063
 __do_sys_sendto net/socket.c:2075 [inline]
 __se_sys_sendto net/socket.c:2071 [inline]
 __x64_sys_sendto+0xe5/0x100 net/socket.c:2071
 x64_sys_call+0x178/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:45
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
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_compound_page+0x78/0xa0 mm/page_alloc.c:828
 destroy_compound_page include/linux/mm.h:1000 [inline]
 __put_compound_page+0x77/0xb0 mm/swap.c:111
 __put_page+0xbc/0xe0 mm/swap.c:127
 put_page include/linux/mm.h:1306 [inline]
 __skb_frag_unref include/linux/skbuff.h:3275 [inline]
 skb_release_data+0x37c/0xa20 net/core/skbuff.c:673
 skb_release_all net/core/skbuff.c:743 [inline]
 __kfree_skb+0x50/0x70 net/core/skbuff.c:757
 sk_eat_skb include/net/sock.h:2800 [inline]
 tcp_recvmsg_locked+0x13d1/0x24f0 net/ipv4/tcp.c:2520
 tcp_recvmsg+0x233/0x770 net/ipv4/tcp.c:2566
 inet_recvmsg+0x13a/0x470 net/ipv4/af_inet.c:861
 sock_recvmsg_nosec net/socket.c:967 [inline]
 sock_recvmsg net/socket.c:985 [inline]
 sock_read_iter+0x2c2/0x380 net/socket.c:1058
 call_read_iter include/linux/fs.h:2206 [inline]
 new_sync_read fs/read_write.c:404 [inline]
 vfs_read+0x6c0/0xc20 fs/read_write.c:485
 ksys_read+0x14a/0x260 fs/read_write.c:623
 __do_sys_read fs/read_write.c:633 [inline]
 __se_sys_read fs/read_write.c:631 [inline]
 __x64_sys_read+0x7b/0x90 fs/read_write.c:631
 x64_sys_call+0x96d/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:1
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80

Memory state around the buggy address:
 ffff888107bcd800: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff888107bcd880: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff888107bcd900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                         ^
 ffff888107bcd980: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff888107bcda00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================
------------[ cut here ]------------
WARNING: CPU: 0 PID: 314 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: 0 PID: 314 Comm: syz-executor637 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: 88 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 d3 88 3e fe <0f> 0b 48 8b 5c 24 38 e9 b1 02 00 00 e8 c2 88 3e fe 49 8d bf 90 02
RSP: 0018:ffffc90000aa7ae0 EFLAGS: 00010093
RAX: ffffffff832b2e0d RBX: 1ffff11020f79b1a RCX: ffff888107fecf00
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: ffffc90000aa7be8 R08: 0000000000000003 R09: 0000000000000004
R10: dffffc0000000000 R11: fffff52000154f4c R12: 0000000000000000
R13: dffffc0000000000 R14: 1ffff92000154f64 R15: ffff888107bcd800
FS:  000055555c9793c0(0000) GS:ffff8881f7000000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007ffc60ddfff0 CR3: 0000000124dc1000 CR4: 00000000003506b0
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: 0033:0x7f25faf29bfe
Code: 08 0f 85 05 e2 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:00007ffeca1b1b48 EFLAGS: 00000246 ORIG_RAX: 0000000000000003
RAX: 0000000000000000 RBX: 000055555c9793c0 RCX: 00007f25faf29bfe
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000003
RBP: 00007ffeca1b1bd0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f25fafafb4c
R13: 00000000000089bd R14: 00007ffeca1b1bf0 R15: 00007f25faee8360
 </TASK>
---[ end trace da04d5a5b1082c37 ]---

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
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
* Struck through repros no longer work on HEAD.