[BUG] lockd: KASAN: slab-use-after-free in nlm_async_call

[BUG] lockd: KASAN: slab-use-after-free in nlm_async_call

[Shuangpeng Bai]

Hi Kernel Maintainers,

I hit the following report while testing current upstream kernel:

KASAN: slab-use-after-free in nlm_async_call

on commit: 3aa1dcaa4f6f5ae08936491e08bd456f331f2d40 (2026-08-13)

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/e0569a211da5a1738fb91b1833465662

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

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

[  193.891339][ T8377] BUG: KASAN: slab-use-after-free in nlm_async_call+0xd6/0x230
[  193.893522][ T8377] Read of size 8 at addr ffff88811b04c808 by task lockd/8377
[  193.895154][ T8377]
[  193.895574][ T8377] Call Trace:
[  193.895578][ T8377]  <TASK>
[  193.895581][ T8377]  dump_stack_lvl+0x26/0x80
[  193.895592][ T8377]  print_report+0x147/0x790
[  193.895619][ T8377]  kasan_report+0xc3/0x100
[  193.895631][ T8377]  nlm_async_call+0xd6/0x230
[  193.895688][ T8377]  nlmsvc_retry_blocked+0x61c/0x800
[  193.895695][ T8377]  lockd+0x144/0x1c0
[  193.895702][ T8377]  kthread+0x2f2/0x3c0
[  193.895722][ T8377]  ret_from_fork+0x27d/0x670
[  193.895747][ T8377]  ret_from_fork_asm+0x1a/0x30
[  193.895754][ T8377]  </TASK>
[  193.913276][ T8377] Allocated by task 8377 on cpu 1 at 181.704904s:
[  193.914652][ T8377]  __kmalloc_cache_noprof+0x248/0x4b0
[  193.915123][ T8377]  nlm_alloc_call+0x4b/0x1b0
[  193.915527][ T8377]  nlmsvc_lock+0x3d2/0xfc0
[  193.915922][ T8377]  nlm4svc_do_lock+0x291/0x480
[  193.916341][ T8377]  nlmsvc_dispatch+0xac/0x1b0
[  193.916752][ T8377]  svc_process_common+0x1229/0x1700
[  193.917211][ T8377]  svc_process+0x26b/0x560
[  193.917601][ T8377]  svc_recv+0x1690/0x1c70
[  193.917986][ T8377]  lockd+0x14e/0x1c0
[  193.919766][ T8377] Freed by task 8392 on cpu 1 at 192.290946s:
[  193.921551][ T8377]  kfree+0x134/0x450
[  193.921895][ T8377]  nlmsvc_release_block+0x231/0x290
[  193.922345][ T8377]  nlmsvc_traverse_blocks+0x139/0x1b0
[  193.922816][ T8377]  nlm_traverse_files+0x1aa/0xa00
[  193.923250][ T8377]  nlmsvc_free_host_resources+0x12/0x60
[  193.923726][ T8377]  nlm_shutdown_hosts_net+0x127/0x280
[  193.924193][ T8377]  lockd_down+0xd5/0x1c0
[  193.924561][ T8377]  nfsd_destroy_serv+0x265/0x400
[  193.924994][ T8377]  nfsd_shutdown_threads+0xbb/0x100
[  193.925443][ T8377]  nfsd_umount+0x3b/0xc0
[  193.925815][ T8377]  deactivate_locked_super+0x9c/0x230
[  193.926279][ T8377]  cleanup_mnt+0x3a8/0x420


Best,
Shuangpeng