Re: [PATCH] binder: fix use-after-free in binderfs_evict_inode()

[Carlos Llamas]

On Mon, Mar 24, 2025 at 04:24:27PM +0300, Dmitry Antipov wrote:
> Running 'stress-ng --binderfs 16 --timeout 300' under KASAN-enabled
> kernel, I've noticed the following:
> 
> BUG: KASAN: slab-use-after-free in binderfs_evict_inode+0x1de/0x2d0
> Write of size 8 at addr ffff88807379bc08 by task stress-ng-binde/1699
> 
> CPU: 0 UID: 0 PID: 1699 Comm: stress-ng-binde Not tainted 6.14.0-rc7-g586de92313fc-dirty #13
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.3-3.fc41 04/01/2014
> Call Trace:
>  <TASK>
>  dump_stack_lvl+0x1c2/0x2a0
>  ? __pfx_dump_stack_lvl+0x10/0x10
>  ? __pfx__printk+0x10/0x10
>  ? __pfx_lock_release+0x10/0x10
>  ? __virt_addr_valid+0x18c/0x540
>  ? __virt_addr_valid+0x469/0x540
>  print_report+0x155/0x840
>  ? __virt_addr_valid+0x18c/0x540
>  ? __virt_addr_valid+0x469/0x540
>  ? __phys_addr+0xba/0x170
>  ? binderfs_evict_inode+0x1de/0x2d0
>  kasan_report+0x147/0x180
>  ? binderfs_evict_inode+0x1de/0x2d0
>  binderfs_evict_inode+0x1de/0x2d0
>  ? __pfx_binderfs_evict_inode+0x10/0x10
>  evict+0x524/0x9f0
>  ? __pfx_lock_release+0x10/0x10
>  ? __pfx_evict+0x10/0x10
>  ? do_raw_spin_unlock+0x4d/0x210
>  ? _raw_spin_unlock+0x28/0x50
>  ? iput+0x697/0x9b0
>  __dentry_kill+0x209/0x660
>  ? shrink_kill+0x8d/0x2c0
>  shrink_kill+0xa9/0x2c0
>  shrink_dentry_list+0x2e0/0x5e0
>  shrink_dcache_parent+0xa2/0x2c0
>  ? __pfx_shrink_dcache_parent+0x10/0x10
>  ? __pfx_lock_release+0x10/0x10
>  ? __pfx_do_raw_spin_lock+0x10/0x10
>  do_one_tree+0x23/0xe0
>  shrink_dcache_for_umount+0xa0/0x170
>  generic_shutdown_super+0x67/0x390
>  kill_litter_super+0x76/0xb0
>  binderfs_kill_super+0x44/0x90
>  deactivate_locked_super+0xb9/0x130
>  cleanup_mnt+0x422/0x4c0
>  ? lockdep_hardirqs_on+0x9d/0x150
>  task_work_run+0x1d2/0x260
>  ? __pfx_task_work_run+0x10/0x10
>  resume_user_mode_work+0x52/0x60
>  syscall_exit_to_user_mode+0x9a/0x120
>  do_syscall_64+0x103/0x210
>  ? asm_sysvec_apic_timer_interrupt+0x1a/0x20
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> RIP: 0033:0xcac57b
> Code: c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 f3 0f 1e fa 31 f6 e9 05 00 00 00 0f 1f 44 00 00 f3 0f 1e fa b8
> RSP: 002b:00007ffecf4226a8 EFLAGS: 00000246 ORIG_RAX: 00000000000000a6
> RAX: 0000000000000000 RBX: 00007ffecf422720 RCX: 0000000000cac57b
> RDX: 0000000000000000 RSI: 0000000000000000 RDI: 00007ffecf422850
> RBP: 00007ffecf422850 R08: 0000000028d06ab1 R09: 7fffffffffffffff
> R10: 3fffffffffffffff R11: 0000000000000246 R12: 00007ffecf422718
> R13: 00007ffecf422710 R14: 00007f478f87b658 R15: 00007ffecf422830
>  </TASK>
> 
> Allocated by task 1705:
>  kasan_save_track+0x3e/0x80
>  __kasan_kmalloc+0x8f/0xa0
>  __kmalloc_cache_noprof+0x213/0x3e0
>  binderfs_binder_device_create+0x183/0xa80
>  binder_ctl_ioctl+0x138/0x190
>  __x64_sys_ioctl+0x120/0x1b0
>  do_syscall_64+0xf6/0x210
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> 
> Freed by task 1705:
>  kasan_save_track+0x3e/0x80
>  kasan_save_free_info+0x46/0x50
>  __kasan_slab_free+0x62/0x70
>  kfree+0x194/0x440
>  evict+0x524/0x9f0
>  do_unlinkat+0x390/0x5b0
>  __x64_sys_unlink+0x47/0x50
>  do_syscall_64+0xf6/0x210
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> 
> This 'stress-ng' workload causes the concurrent deletions from
> 'binder_devices' and so requires full-featured synchronization
> to prevent list corruption.
> 
> I've found this issue independently but pretty sure that syzbot did
> the same, so Reported-by: and Closes: should be applicable here as well.
> 
> Reported-by: syzbot+353d7b75658a95aa955a@xxxxxxxxxxxxxxxxxxxxxxxxx
> Closes: https://syzkaller.appspot.com/bug?extid=353d7b75658a95aa955a
> Fixes: e77aff5528a18 ("binderfs: fix use-after-free in binder_devices")
> Signed-off-by: Dmitry Antipov <dmantipov@xxxxxxxxx>
> ---

Thanks Dmitry, I was just running an almost identical fix. :)

Acked-by: Carlos Llamas <cmllamas@xxxxxxxxxx>