possible deadlock in uvcg_default_output_i_terminal_show

Status: upstream: reported on 2026/08/12 00:11
Subsystems: usb
Labels: prio:low
[Documentation on labels]
Reported-by: syzbot+a5ab3e09c246a659fe9c@syzkaller.appspotmail.com
First crash: 6d18h, last: 6d18h
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ID Workflow Result Correct Bug Created Started Finished Revision
0a692c58 assessment-security DenialOfService: ❌ Exploitable: ❌ FilesystemTrigger: ❌ NetworkTrigger: ❌ PeripheralTrigger: ❌ RemoteTrigger: ❌ Unprivileged: ❌ UserNamespace: ❌ VMGuestTrigger: ❌ VMHostTrigger: ❌ ❓ possible deadlock in uvcg_default_output_i_terminal_show 2026/08/08 21:32 2026/08/08 21:32 2026/08/08 22:04 5d63f80b
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[syzbot] [usb?] possible deadlock in uvcg_default_output_i_terminal_show 0 (1) 2026/08/12 00:11

Sample crash report:
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Tainted: G             L     
------------------------------------------------------
syz.5.3720/17064 is trying to acquire lock:
ffffffff901d0fe8 (gadget_subsys.su_mutex){+.+.}-{4:4}, at: uvcg_default_output_i_terminal_show+0x49/0x180 drivers/usb/gadget/function/uvc_configfs.c:671

but task is already holding lock:
ffff888025961970 (&p->frag_sem){++++}-{4:4}, at: fill_read_buffer fs/configfs/file.c:66 [inline]
ffff888025961970 (&p->frag_sem){++++}-{4:4}, at: configfs_read_iter+0x346/0x6f0 fs/configfs/file.c:88

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #3 (&p->frag_sem){++++}-{4:4}:
       lock_acquire kernel/locking/lockdep.c:5868 [inline]
       lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5825
       down_write_killable+0x93/0x250 kernel/locking/rwsem.c:1643
       configfs_rmdir+0x3fa/0x950 fs/configfs/dir.c:1534
       vfs_rmdir fs/namei.c:5381 [inline]
       vfs_rmdir+0x328/0x8a0 fs/namei.c:5354
       filename_rmdir+0x31a/0x5c0 fs/namei.c:5438
       __do_sys_rmdir fs/namei.c:5461 [inline]
       __se_sys_rmdir fs/namei.c:5458 [inline]
       __x64_sys_rmdir+0x46/0x70 fs/namei.c:5458
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0x115/0x870 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #2 (&sb->s_type->i_mutex_key#24){++++}-{4:4}:
       lock_acquire kernel/locking/lockdep.c:5868 [inline]
       lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5825
       down_write+0x8b/0x1f0 kernel/locking/rwsem.c:1631
       inode_lock include/linux/fs.h:1024 [inline]
       configfs_depend_item_unlocked+0xf3/0x6a0 fs/configfs/dir.c:1259
       usbg_make_tpg+0x261/0x620 drivers/usb/gadget/function/f_tcm.c:1686
       target_fabric_make_tpg+0xab/0x8c0 drivers/target/target_core_fabric_configfs.c:939
       configfs_mkdir+0x51e/0xb70 fs/configfs/dir.c:1360
       vfs_mkdir+0x361/0x850 fs/namei.c:5276
       filename_mkdirat+0x48b/0x5e0 fs/namei.c:5309
       __do_sys_mkdirat fs/namei.c:5330 [inline]
       __se_sys_mkdirat fs/namei.c:5327 [inline]
       __x64_sys_mkdirat+0x89/0xc0 fs/namei.c:5327
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0x115/0x870 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (&opts->dep_lock){+.+.}-{4:4}:
       lock_acquire kernel/locking/lockdep.c:5868 [inline]
       lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5825
       __mutex_lock_common kernel/locking/mutex.c:646 [inline]
       __mutex_lock+0x1a4/0x1bd0 kernel/locking/mutex.c:821
       tcm_set_name+0x29/0xb0 drivers/usb/gadget/function/f_tcm.c:2669
       function_make+0x21c/0x3f0 drivers/usb/gadget/configfs.c:636
       configfs_mkdir+0x51e/0xb70 fs/configfs/dir.c:1360
       vfs_mkdir+0x361/0x850 fs/namei.c:5276
       filename_mkdirat+0x48b/0x5e0 fs/namei.c:5309
       __do_sys_mkdirat fs/namei.c:5330 [inline]
       __se_sys_mkdirat fs/namei.c:5327 [inline]
       __x64_sys_mkdirat+0x89/0xc0 fs/namei.c:5327
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0x115/0x870 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0
 (
gadget_subsys.su_mutex){+.+.}-{4:4}:
       check_prev_add+0xeb/0xe60 kernel/locking/lockdep.c:3165
       check_prevs_add kernel/locking/lockdep.c:3284 [inline]
       validate_chain kernel/locking/lockdep.c:3908 [inline]
       __lock_acquire+0x136c/0x1a40 kernel/locking/lockdep.c:5237
       lock_acquire kernel/locking/lockdep.c:5868 [inline]
       lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5825
       __mutex_lock_common kernel/locking/mutex.c:646 [inline]
       __mutex_lock+0x1a4/0x1bd0 kernel/locking/mutex.c:821
       uvcg_default_output_i_terminal_show+0x49/0x180 drivers/usb/gadget/function/uvc_configfs.c:671
       fill_read_buffer fs/configfs/file.c:68 [inline]
       configfs_read_iter+0x426/0x6f0 fs/configfs/file.c:88
       __kernel_read+0x397/0xad0 fs/read_write.c:532
       integrity_kernel_read+0x7e/0xb0 security/integrity/iint.c:28
       ima_calc_file_hash_tfm+0x25e/0x350 security/integrity/ima/ima_crypto.c:222
       ima_calc_file_hash+0x1e3/0x380 security/integrity/ima/ima_crypto.c:280
       ima_collect_measurement+0x94f/0xb30 security/integrity/ima/ima_api.c:300
       process_measurement+0xdfe/0x2350 security/integrity/ima/ima_main.c:425
       ima_file_check+0xc3/0x110 security/integrity/ima/ima_main.c:685
       security_file_post_open+0xc4/0x210 security/security.c:2755
       do_open fs/namei.c:4702 [inline]
       path_openat+0x985/0x4280 fs/namei.c:4863
       do_file_open+0x20e/0x430 fs/namei.c:4892
       do_sys_openat2+0x10f/0x1e0 fs/open.c:1368
       do_sys_open fs/open.c:1374 [inline]
       __do_sys_openat fs/open.c:1390 [inline]
       __se_sys_openat fs/open.c:1385 [inline]
       __x64_sys_openat+0x12d/0x210 fs/open.c:1385
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0x115/0x870 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

other info that might help us debug this:

Chain exists of:
  gadget_subsys.su_mutex --> &sb->s_type->i_mutex_key#24 --> &p->frag_sem

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  rlock(&p->frag_sem);
                               lock(&sb->s_type->i_mutex_key#24);
                               lock(&p->frag_sem);
  lock(gadget_subsys.su_mutex);

 *** DEADLOCK ***

3 locks held by syz.5.3720/17064:
 #0: ffff88802bcb8ab0 (&ima_iint_mutex_key[depth]){+.+.}-{4:4}, at: process_measurement+0x5ab/0x2350 security/integrity/ima/ima_main.c:319
 #1: ffff888053449c80 (&buffer->mutex){+.+.}-{4:4}, at: configfs_read_iter+0x79/0x6f0 fs/configfs/file.c:86
 #2: ffff888025961970 (&p->frag_sem){++++}-{4:4}, at: fill_read_buffer fs/configfs/file.c:66 [inline]
 #2: ffff888025961970 (&p->frag_sem){++++}-{4:4}, at: configfs_read_iter+0x346/0x6f0 fs/configfs/file.c:88

stack backtrace:
CPU: 1 UID: 0 PID: 17064 Comm: syz.5.3720 Tainted: G             L      syzkaller #0 PREEMPT(full) 
Tainted: [L]=SOFTLOCKUP
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x100/0x190 lib/dump_stack.c:120
 print_circular_bug.cold+0x178/0x1c7 kernel/locking/lockdep.c:2043
 check_noncircular+0x146/0x160 kernel/locking/lockdep.c:2175
 check_prev_add+0xeb/0xe60 kernel/locking/lockdep.c:3165
 check_prevs_add kernel/locking/lockdep.c:3284 [inline]
 validate_chain kernel/locking/lockdep.c:3908 [inline]
 __lock_acquire+0x136c/0x1a40 kernel/locking/lockdep.c:5237
 lock_acquire kernel/locking/lockdep.c:5868 [inline]
 lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5825
 __mutex_lock_common kernel/locking/mutex.c:646 [inline]
 __mutex_lock+0x1a4/0x1bd0 kernel/locking/mutex.c:821
 uvcg_default_output_i_terminal_show+0x49/0x180 drivers/usb/gadget/function/uvc_configfs.c:671
 fill_read_buffer fs/configfs/file.c:68 [inline]
 configfs_read_iter+0x426/0x6f0 fs/configfs/file.c:88
 __kernel_read+0x397/0xad0 fs/read_write.c:532
 integrity_kernel_read+0x7e/0xb0 security/integrity/iint.c:28
 ima_calc_file_hash_tfm+0x25e/0x350 security/integrity/ima/ima_crypto.c:222
 ima_calc_file_hash+0x1e3/0x380 security/integrity/ima/ima_crypto.c:280
 ima_collect_measurement+0x94f/0xb30 security/integrity/ima/ima_api.c:300
 process_measurement+0xdfe/0x2350 security/integrity/ima/ima_main.c:425
 ima_file_check+0xc3/0x110 security/integrity/ima/ima_main.c:685
 security_file_post_open+0xc4/0x210 security/security.c:2755
 do_open fs/namei.c:4702 [inline]
 path_openat+0x985/0x4280 fs/namei.c:4863
 do_file_open+0x20e/0x430 fs/namei.c:4892
 do_sys_openat2+0x10f/0x1e0 fs/open.c:1368
 do_sys_open fs/open.c:1374 [inline]
 __do_sys_openat fs/open.c:1390 [inline]
 __se_sys_openat fs/open.c:1385 [inline]
 __x64_sys_openat+0x12d/0x210 fs/open.c:1385
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x115/0x870 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fb58099e0d9
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:00007fb581891028 EFLAGS: 00000246 ORIG_RAX: 0000000000000101
RAX: ffffffffffffffda RBX: 00007fb580c25fa0 RCX: 00007fb58099e0d9
RDX: 0000000000000000 RSI: 0000200000000800 RDI: ffffffffffffff9c
RBP: 00007fb580a35024 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fb580c26038 R14: 00007fb580c25fa0 R15: 00007ffec8a97b18
 </TASK>

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/08/06 14:00 upstream 0d8395707651 cc56899a .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream possible deadlock in uvcg_default_output_i_terminal_show
* Struck through repros no longer work on HEAD.