Re: [BUG] KASAN: slab-use-after-free in _copy_to_user from platform/x86/dell-smbios-wmi

[Armin Wolf]

Am 14.06.26 um 21:15 schrieb Shuangpeng Bai:

> Hi Kernel Maintainers,
>
> I hit the following report while testing current upstream kernel:
>
> KASAN: slab-use-after-free in _copy_to_user from platform/x86/dell-smbios-wmi
>
> on commit: e8c2f9fdadee7cbc75134dc463c1e0d856d6e5c7 (May 25 2026)
>
> The reproducer and .config files are here.
> https://gist.github.com/shuangpengbai/f5b15c099e80897486b4238ddb91df79
>
> I'm happy to test debug patches or provide additional information.

It seems that unbinding the dell-smbios-wmi driver races with any outstanding
file operations on the misc device, causing them to access memory already freed
by the unbound driver.

I do not know if the misc device synchronizes file operations against removal,
but i do not think that this is the case. I added the maintains of the char drivers
to the discussion, maybe they know this.

Thanks,
Armin Wolf

> Reported-by: Shuangpeng Bai <shuangpeng.kernel@xxxxxxxxx>
>
> [   92.502430][ T8394] BUG: KASAN: slab-use-after-free in _copy_to_user (include/linux/instrumented.h:129 include/linux/uaccess.h:205 lib/usercopy.c:26)
> [   92.504528][ T8394] Read of size 8 at addr ffff888126eec360 by task dell_smbios_wmi/8394
> [   92.506899][ T8394] 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
> [   92.506905][ T8394] Call Trace:
> [   92.506914][ T8394]  <TASK>
> [   92.506919][ T8394]  dump_stack_lvl (lib/dump_stack.c:94 lib/dump_stack.c:120)
> [   92.506931][ T8394]  print_report (mm/kasan/report.c:378 mm/kasan/report.c:482)
> [   92.506956][ T8394]  kasan_report (mm/kasan/report.c:595)
> [   92.506972][ T8394]  kasan_check_range (mm/kasan/generic.c:? mm/kasan/generic.c:200)
> [   92.506979][ T8394]  _copy_to_user (include/linux/instrumented.h:129 include/linux/uaccess.h:205 lib/usercopy.c:26)
> [   92.506986][ T8394]  simple_read_from_buffer (include/linux/uaccess.h:236 fs/libfs.c:1155)
> [   92.506998][ T8394]  vfs_read (fs/read_write.c:572)
> [   92.507049][ T8394]  ksys_read (fs/read_write.c:717)
> [   92.507072][ T8394]  do_syscall_64 (arch/x86/entry/syscall_64.c:63 arch/x86/entry/syscall_64.c:94)
> [   92.507095][ T8394]  entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:121)
> [   92.507163][ T8394]  </TASK>
> [   92.530149][ T8394] Freed by task 8394 on cpu 0 at 92.299564s:
> [   92.530733][ T8394]  kasan_save_track (mm/kasan/common.c:57 mm/kasan/common.c:78)
> [   92.531183][ T8394]  kasan_save_free_info (mm/kasan/generic.c:584)
> [   92.531673][ T8394]  __kasan_slab_free (mm/kasan/common.c:253 mm/kasan/common.c:285)
> [   92.532133][ T8394]  kfree (include/linux/kasan.h:235 mm/slub.c:2689 mm/slub.c:6251 mm/slub.c:6566)
> [   92.532509][ T8394]  devres_release_all (drivers/base/devres.c:50 drivers/base/devres.c:547 drivers/base/devres.c:576)
> [   92.533000][ T8394]  device_release_driver_internal (drivers/base/dd.c:598 drivers/base/dd.c:1357 drivers/base/dd.c:1375)
> [   92.533574][ T8394]  unbind_store (drivers/base/bus.c:244)
> [   92.534021][ T8394]  kernfs_fop_write_iter (fs/kernfs/file.c:352)
> [   92.534531][ T8394]  vfs_write (fs/read_write.c:595 fs/read_write.c:688)
> [   92.534950][ T8394]  ksys_write (fs/read_write.c:740)
> [   92.535364][ T8394]  do_syscall_64 (arch/x86/entry/syscall_64.c:63 arch/x86/entry/syscall_64.c:94)
> [   92.535811][ T8394]  entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:121)
> [   92.536610][ T8394] The buggy address belongs to the object at ffff888126eec300
> [   92.536610][ T8394]  which belongs to the cache kmalloc-192 of size 192
> [   92.537941][ T8394] The buggy address is located 96 bytes inside of
> [   92.537941][ T8394]  freed 192-byte region [ffff888126eec300, ffff888126eec3c0)
>
>
> Best,
> Shuangpeng