syzbot


WARNING: refcount bug in bnep_session (2)

Status: moderation: reported on 2026/05/15 12:38
Subsystems: kernel
[Documentation on labels]
Reported-by: syzbot+69778c8531605ad81b57@syzkaller.appspotmail.com
First crash: 4d20h, last: 4d20h
✨ AI Jobs (1)
ID Workflow Result Correct Bug Created Started Finished Revision Error
3528dd6c-522d-4589-b276-995a65ce1784 assessment-security 💥 WARNING: refcount bug in bnep_session (2) 2026/05/15 05:25 2026/05/15 05:25 2026/05/15 05:27 6ccb967e465e832a7bfd7a116ad00d52a0923a5d failed to run ["make" "KERNELVERSION=syzkaller" "KERNELRELEASE=syzkaller" "LOCALVERSION=-syzkaller" "-j" "32" "ARCH=x86_64" "CC=ccache clang" "LD=ld.lld" "O=/app/workdir/cache/build/2054c2e912eb67edb977119539f2ce3a8137a0b6" "-s" "bzImage" "compile_commands.json"]: exit status 2 * * Restart config... * * * General architecture-dependent options * SMT (Hyperthreading) scheduler support (SCHED_SMT) [Y/?] y Cluster scheduler support (SCHED_CLUSTER) [Y/n/?] y Multi-Core Cache (MC) scheduler support (SCHED_MC) [Y/n/?] y Kprobes (KPROBES) [N/y/?] n Optimize very unlikely/likely branches (JUMP_LABEL) [Y/n/?] y Static key selftest (STATIC_KEYS_SELFTEST) [N/y/?] n Static call selftest (STATIC_CALL_SELFTEST) [N/y/?] n Enable seccomp to safely execute untrusted bytecode (SECCOMP) [Y/n/?] y Show seccomp filter cache status in /proc/pid/seccomp_cache (SECCOMP_CACHE_DEBUG) [N/y/?] n Stack Protector buffer overflow detection (STACKPROTECTOR) [Y/n/?] y Strong Stack Protector (STACKPROTECTOR_STRONG) [Y/n/?] y Link Time Optimization (LTO) > 1. None (LTO_NONE) choice[1]: 1 Enable Clang's AutoFDO build (EXPERIMENTAL) (AUTOFDO_CLANG) [N/y/?] (NEW) Error in reading or end of file. Enable Clang's Propeller build (PROPELLER_CLANG) [N/y/?] (NEW) Error in reading or end of file. Use Kernel Control Flow Integrity (kCFI) (CFI) [N/y/?] (NEW) Error in reading or end of file. Number of bits to use for ASLR of mmap base address (ARCH_MMAP_RND_BITS) [28] 28 Number of bits to use for ASLR of mmap base address for compatible applications (ARCH_MMAP_RND_COMPAT_BITS) [8] 8 MMU page size > 1. 4KiB pages (PAGE_SIZE_4KB) choice[1]: 1 Provide system calls for 32-bit time_t (COMPAT_32BIT_TIME) [Y/n/?] y Use a virtually-mapped stack (VMAP_STACK) [Y/n/?] y Support for randomizing kernel stack offset on syscall entry (RANDOMIZE_KSTACK_OFFSET) [Y/n/?] y Default state of kernel stack offset randomization (RANDOMIZE_KSTACK_OFFSET_DEFAULT) [N/y/?] n Locking event counts collection (LOCK_EVENT_COUNTS) [N/y/?] n * * Memory initialization * Initialize kernel stack variables at function entry 1. no automatic stack variable initialization (weakest) (INIT_STACK_NONE) 2. pattern-init everything (strongest) (INIT_STACK_ALL_PATTERN) > 3. zero-init everything (strongest and safest) (INIT_STACK_ALL_ZERO) choice[1-3?]: 3 Poison kernel stack before returning from syscalls (KSTACK_ERASE) [N/y/?] (NEW) Error in reading or end of file. Enable heap memory zeroing on allocation by default (INIT_ON_ALLOC_DEFAULT_ON) [Y/n/?] y Enable heap memory zeroing on free by default (INIT_ON_FREE_DEFAULT_ON) [N/y/?] n Enable register zeroing on function exit (ZERO_CALL_USED_REGS) [N/y/?] n * * Kernel hardening options * Randomize layout of sensitive kernel structures > 1. Disable structure layout randomization (RANDSTRUCT_NONE) 2. Fully randomize structure layout (RANDSTRUCT_FULL) (NEW) choice[1-2?]: Error in reading or end of file. /app/workdir/cache/src/ecd8bb68855fdd08aa08215ac485989bac875215/lib/maple_tree.c:3514:20: warning: stack frame size (2424) exceeds limit (2048) in 'mas_wr_store_entry' [-Wframe-larger-than] 3514 | static inline void mas_wr_store_entry(struct ma_wr_state *wr_mas) | ^ 1 warning generated. /app/workdir/cache/src/ecd8bb68855fdd08aa08215ac485989bac875215/sound/usb/mixer_s1810c.c:634:5: warning: stack frame size (2360) exceeds limit (2048) in 'snd_sc1810_init_mixer' [-Wframe-larger-than] 634 | int snd_sc1810_init_mixer(struct usb_mixer_interface *mixer) | ^ 1 warning generated. fatal error: error in backend: IO failure on output stream: No space left on device PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace, preprocessed source, and associated run script. Stack dump: 0. Program arguments: /usr/bin/clang --target=x86_64-linux-gnu -fintegrated-as -Werror=unknown-warning-option -Werror=ignored-optimization-argument -Werror=option-ignored -Werror=unused-command-line-argument -fmacro-prefix-map=/app/workdir/cache/src/ecd8bb68855fdd08aa08215ac485989bac875215/= -fsho
Similar bugs (1)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream WARNING: refcount bug in bnep_session kernel 13 149 116d 534d 0/29 auto-obsoleted due to no activity on 2026/03/30 12:30

Sample crash report:
------------[ cut here ]------------
refcount_t: underflow; use-after-free.
WARNING: lib/refcount.c:28 at refcount_warn_saturate+0xf4/0x130 lib/refcount.c:28, CPU#1: kbnepd bnep0/6521
Modules linked in:
CPU: 1 UID: 0 PID: 6521 Comm: kbnepd bnep0 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
RIP: 0010:refcount_warn_saturate+0xf4/0x130 lib/refcount.c:28
Code: cc e8 30 3b 0f fd 48 8d 3d 89 d1 e8 0b 67 48 0f b9 3a e8 1f 3b 0f fd 5b 5d e9 58 4f 94 06 e8 13 3b 0f fd 48 8d 3d 7c d1 e8 0b <67> 48 0f b9 3a e8 02 3b 0f fd 5b 5d c3 cc cc cc cc e8 f6 3a 0f fd
RSP: 0018:ffffc900059ff958 EFLAGS: 00010293
RAX: 0000000000000000 RBX: ffff888052bcdc78 RCX: ffffffff84f96b3b
RDX: ffff888020be8000 RSI: ffffffff84f96bcd RDI: ffffffff90e23d50
RBP: 0000000000000003 R08: 0000000000000005 R09: 0000000000000004
R10: 0000000000000003 R11: 0000000000000000 R12: ffff88802b509000
R13: ffff888052bcdc78 R14: ffffffff86352db0 R15: 0000000000000000
FS:  0000000000000000(0000) GS:ffff888124472000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fea969ea4c0 CR3: 000000005c73e000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 __refcount_sub_and_test include/linux/refcount.h:400 [inline]
 __refcount_dec_and_test include/linux/refcount.h:432 [inline]
 refcount_dec_and_test include/linux/refcount.h:450 [inline]
 kref_put include/linux/kref.h:64 [inline]
 klist_dec_and_del lib/klist.c:206 [inline]
 klist_put+0x18a/0x1d0 lib/klist.c:217
 device_del+0x1b8/0x9b0 drivers/base/core.c:3872
 unregister_netdevice_many_notify+0x179e/0x24f0 net/core/dev.c:12453
 unregister_netdevice_many net/core/dev.c:12481 [inline]
 unregister_netdevice_queue net/core/dev.c:12291 [inline]
 unregister_netdevice_queue+0x30b/0x3c0 net/core/dev.c:12281
 unregister_netdevice include/linux/netdevice.h:3444 [inline]
 unregister_netdev+0x1f/0x60 net/core/dev.c:12499
 bnep_session+0x223f/0x2d90 net/bluetooth/bnep/core.c:532
 kthread+0x370/0x450 kernel/kthread.c:436
 ret_from_fork+0x72b/0xd50 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>
----------------
Code disassembly (best guess):
   0:	cc                   	int3
   1:	e8 30 3b 0f fd       	call   0xfd0f3b36
   6:	48 8d 3d 89 d1 e8 0b 	lea    0xbe8d189(%rip),%rdi        # 0xbe8d196
   d:	67 48 0f b9 3a       	ud1    (%edx),%rdi
  12:	e8 1f 3b 0f fd       	call   0xfd0f3b36
  17:	5b                   	pop    %rbx
  18:	5d                   	pop    %rbp
  19:	e9 58 4f 94 06       	jmp    0x6944f76
  1e:	e8 13 3b 0f fd       	call   0xfd0f3b36
  23:	48 8d 3d 7c d1 e8 0b 	lea    0xbe8d17c(%rip),%rdi        # 0xbe8d1a6
* 2a:	67 48 0f b9 3a       	ud1    (%edx),%rdi <-- trapping instruction
  2f:	e8 02 3b 0f fd       	call   0xfd0f3b36
  34:	5b                   	pop    %rbx
  35:	5d                   	pop    %rbp
  36:	c3                   	ret
  37:	cc                   	int3
  38:	cc                   	int3
  39:	cc                   	int3
  3a:	cc                   	int3
  3b:	e8 f6 3a 0f fd       	call   0xfd0f3b36

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/05/11 12:31 upstream 5d6919055dec e6eb7c0b .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-selinux-root WARNING: refcount bug in bnep_session
* Struck through repros no longer work on HEAD.