[BUG] KASAN: slab-use-after-free in mutex_lock from vduse

[Shuangpeng Bai <shuangpeng.kernel@gmail.com>]

Hi Kernel Maintainers,

I hit the following report while testing current upstream kernel:

KASAN: slab-use-after-free in mutex_lock from vduse

I reproduced this on commit: e8c2f9fdadee7cbc75134dc463c1e0d856d6e5c7 (May 25 2026)

To help trigger the bug more reliably, we applied a minimal diagnostic patch
that only adds delays and print statements.

The reproducer and .config files are here.
https://gist.github.com/shuangpengbai/947d604f1b5d86d8b7a3c7a4000455ad

I'm happy to test debug patches or provide additional information.

Reported-by: Shuangpeng Bai <shuangpeng.kernel@gmail.com>

[  111.459938][ T8370] BUG: KASAN: slab-use-after-free in mutex_lock (include/linux/instrumented.h:112 include/linux/atomic/atomic-instrumented.h:4456 kernel/locking/mutex.c:161 kernel/locking/mutex.c:318)
[  111.460790][ T8370] Write of size 8 at addr ffff88811bb7a028 by task vduse_open_dest/8370
[  111.461901][ T8370]
[  111.462229][ T8370] Hardware name: QEMU Ubuntu 24.04 PC v2 (i440FX + PIIX, arch_caps fix, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
[  111.462233][ T8370] Call Trace:
[  111.462238][ T8370]  <TASK>
[  111.462240][ T8370]  dump_stack_lvl (lib/dump_stack.c:94 lib/dump_stack.c:120)
[  111.462249][ T8370]  print_report (mm/kasan/report.c:378 mm/kasan/report.c:482)
[  111.462265][ T8370]  kasan_report (mm/kasan/report.c:595)
[  111.462285][ T8370]  kasan_check_range (mm/kasan/generic.c:? mm/kasan/generic.c:200)
[  111.462290][ T8370]  mutex_lock (include/linux/instrumented.h:112 include/linux/atomic/atomic-instrumented.h:4456 kernel/locking/mutex.c:161 kernel/locking/mutex.c:318)
[  111.462311][ T8370]  vduse_dev_open (drivers/vdpa/vdpa_user/vduse_dev.c:1663)
[  111.462327][ T8370]  chrdev_open (fs/char_dev.c:411)
[  111.462347][ T8370]  do_dentry_open (fs/open.c:947)
[  111.462356][ T8370]  vfs_open (fs/open.c:1079)
[  111.462361][ T8370]  path_openat (fs/namei.c:4699 fs/namei.c:4858)
[  111.462384][ T8370]  do_file_open (fs/namei.c:4887)
[  111.462436][ T8370]  do_sys_openat2 (fs/open.c:1364)
[  111.462462][ T8370]  __x64_sys_openat (fs/open.c:1370 fs/open.c:1386 fs/open.c:1381 fs/open.c:1381)
[  111.462479][ T8370]  do_syscall_64 (arch/x86/entry/syscall_64.c:63 arch/x86/entry/syscall_64.c:94)
[  111.462486][ T8370]  entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:121)
[  111.462492][ T8370] RIP: 0033:0x7facc56097e4
[  111.462497][ T8370] Code: 84 00 00 00 00 00 44 89 54 24 0c e8 36 f5 ff ff 44 8b 54 24 0c 44 89 e2 48 89 ee 41 89 c0 bf 9c ff ff ff b8 01 01 00 00 0f 05 <48> 3d 00 f0 ff ff 77 34 44 89 c7 89 44 24 0c e8 68 f5 ff ff 8b 44
[  111.462502][ T8370] RSP: 002b:00007facc2418e70 EFLAGS: 00000293 ORIG_RAX: 0000000000000101
[  111.462509][ T8370] RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007facc56097e4
[  111.462512][ T8370] RDX: 0000000000080002 RSI: 00007ffe00ff5eb0 RDI: 00000000ffffff9c
[  111.462515][ T8370] RBP: 00007ffe00ff5eb0 R08: 0000000000000000 R09: 00007facc2419700
[  111.462518][ T8370] R10: 0000000000000000 R11: 0000000000000293 R12: 0000000000080002
[  111.462520][ T8370] R13: 00007ffe00ff5ccf R14: 00007facc2418fc0 R15: 0000000000802000
[  111.462526][ T8370]  </TASK>
[  111.462528][ T8370]
[  111.465710][ T8370] Freed by task 8361 on cpu 1 at 111.442076s:
[  111.465718][ T8370]  kasan_save_track (mm/kasan/common.c:57 mm/kasan/common.c:78)
[  111.467048][ T8370]  kasan_save_free_info (mm/kasan/generic.c:584)
[  111.467993][ T8370]  __kasan_slab_free (mm/kasan/common.c:253 mm/kasan/common.c:285)
[  111.469000][ T8370]  kfree (include/linux/kasan.h:235 mm/slub.c:2689 mm/slub.c:6251 mm/slub.c:6566)
[  111.469887][ T8370]  vduse_ioctl (drivers/vdpa/vdpa_user/vduse_dev.c:1866 drivers/vdpa/vdpa_user/vduse_dev.c:1908 drivers/vdpa/vdpa_user/vduse_dev.c:2208)
[  111.470848][ T8370]  __se_sys_ioctl (fs/ioctl.c:51 fs/ioctl.c:597 fs/ioctl.c:583)
[  111.471775][ T8370]  do_syscall_64 (arch/x86/entry/syscall_64.c:63 arch/x86/entry/syscall_64.c:94)
[  111.472940][ T8370]  entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:121)
[  111.473875][ T8370]
[  111.475022][ T8370] The buggy address belongs to the object at ffff88811bb7a000
[  111.475022][ T8370]  which belongs to the cache kmalloc-512 of size 512
[  111.475948][ T8370] The buggy address is located 40 bytes inside of
[  111.475948][ T8370]  freed 512-byte region [ffff88811bb7a000, ffff88811bb7a200)
[  111.476936][ T8370]


Best,
Shuangpeng