[BUG] ptp: vmclock: KASAN slab-use-after-free in vmclock_miscdev_read

[BUG] ptp: vmclock: KASAN slab-use-after-free in vmclock_miscdev_read

[Shuangpeng Bai]

Hi,

I hit the following KASAN report while testing current upstream kernel.

The issue was reproduced by opening /dev/vmclock0, unbinding the vmclock
platform device, and then reading from the old fd.

KASAN: slab-use-after-free in vmclock_miscdev_read

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

The reproducer and .config files are here.
https://gist.github.com/shuangpengbai/7c2d117852611448a80026f8aa4d4bc4

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

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

[  148.011605][ T8390] BUG: KASAN: slab-use-after-free in vmclock_miscdev_read (drivers/ptp/ptp_vmclock.c:409)
[  148.015241][ T8390] Read of size 8 at addr ffff88811fdc7478 by task repro_vmclock_o/8390
[  148.018209][ T8390] 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
[  148.018216][ T8390] Call Trace:
[  148.018226][ T8390]  <TASK>
[  148.018232][ T8390]  dump_stack_lvl (lib/dump_stack.c:94 lib/dump_stack.c:120)
[  148.018248][ T8390]  print_report (mm/kasan/report.c:378 mm/kasan/report.c:482)
[  148.018314][ T8390]  kasan_report (mm/kasan/report.c:595)
[  148.018335][ T8390]  vmclock_miscdev_read (drivers/ptp/ptp_vmclock.c:409)
[  148.018384][ T8390]  vfs_read (fs/read_write.c:572)
[  148.018453][ T8390]  __x64_sys_pread64 (fs/read_write.c:765 fs/read_write.c:773 fs/read_write.c:770 fs/read_write.c:770)
[  148.018483][ T8390]  do_syscall_64 (arch/x86/entry/syscall_64.c:63 arch/x86/entry/syscall_64.c:94)
[  148.018498][ T8390]  entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:121)
[  148.018604][ T8390]  </TASK>
[  148.042173][ T8390] Freed by task 8390 on cpu 1 at 147.908511s:
[  148.042791][ T8390]  kasan_save_track (mm/kasan/common.c:57 mm/kasan/common.c:78)
[  148.043265][ T8390]  kasan_save_free_info (mm/kasan/generic.c:584)
[  148.043775][ T8390]  __kasan_slab_free (mm/kasan/common.c:253 mm/kasan/common.c:285)
[  148.044256][ T8390]  kfree (include/linux/kasan.h:235 mm/slub.c:2689 mm/slub.c:6251 mm/slub.c:6566)
[  148.044668][ T8390]  devres_release_all (drivers/base/devres.c:50 drivers/base/devres.c:547 drivers/base/devres.c:576)
[  148.045171][ T8390]  device_release_driver_internal (drivers/base/dd.c:598 drivers/base/dd.c:1357 drivers/base/dd.c:1375)
[  148.045791][ T8390]  unbind_store (drivers/base/bus.c:244)
[  148.046252][ T8390]  kernfs_fop_write_iter (fs/kernfs/file.c:352)
[  148.046798][ T8390]  vfs_write (fs/read_write.c:595 fs/read_write.c:688)
[  148.047229][ T8390]  ksys_write (fs/read_write.c:740)
[  148.047678][ T8390]  do_syscall_64 (arch/x86/entry/syscall_64.c:63 arch/x86/entry/syscall_64.c:94)
[  148.048144][ T8390]  entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:121)
[  148.048996][ T8390] The buggy address belongs to the object at ffff88811fdc7400
[  148.048996][ T8390]  which belongs to the cache kmalloc-512 of size 512
[  148.050394][ T8390] The buggy address is located 120 bytes inside of
[  148.050394][ T8390]  freed 512-byte region [ffff88811fdc7400, ffff88811fdc7600)


Best,
Shuangpeng