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[PATCH] f2fs: fix to avoid use-after-free in f2fs_stop_gc_thread()

Chao Yu posted 1 patch 1 year, 6 months ago
There is a newer version of this series
fs/f2fs/file.c | 3 +++
1 file changed, 3 insertions(+)
[PATCH] f2fs: fix to avoid use-after-free in f2fs_stop_gc_thread()
Posted by Chao Yu 1 year, 6 months ago 
syzbot reports a f2fs bug as below:

 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0x241/0x360 lib/dump_stack.c:114
 print_report+0xe8/0x550 mm/kasan/report.c:491
 kasan_report+0x143/0x180 mm/kasan/report.c:601
 kasan_check_range+0x282/0x290 mm/kasan/generic.c:189
 instrument_atomic_read_write include/linux/instrumented.h:96 [inline]
 atomic_fetch_add_relaxed include/linux/atomic/atomic-instrumented.h:252 [inline]
 __refcount_add include/linux/refcount.h:184 [inline]
 __refcount_inc include/linux/refcount.h:241 [inline]
 refcount_inc include/linux/refcount.h:258 [inline]
 get_task_struct include/linux/sched/task.h:118 [inline]
 kthread_stop+0xca/0x630 kernel/kthread.c:704
 f2fs_stop_gc_thread+0x65/0xb0 fs/f2fs/gc.c:210
 f2fs_do_shutdown+0x192/0x540 fs/f2fs/file.c:2283
 f2fs_ioc_shutdown fs/f2fs/file.c:2325 [inline]
 __f2fs_ioctl+0x443a/0xbe60 fs/f2fs/file.c:4325
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:907 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:893
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

The root cause is below race condition, it may cause use-after-free
issue in sbi->gc_th pointer.

- remount
 - f2fs_remount
  - f2fs_stop_gc_thread
   - kfree(gc_th)
				- f2fs_ioc_shutdown
				 - f2fs_do_shutdown
				  - f2fs_stop_gc_thread
				   - kthread_stop(gc_th->f2fs_gc_task)

We will call f2fs_do_shutdown() in two paths:
- for f2fs_ioc_shutdown() path, we should grab sb->s_umount semaphore
for fixing.
- for f2fs_shutdown() path, it's safe since caller has already grabbed
sb->s_umount semaphore.

Reported-by: syzbot+1a8e2b31f2ac9bd3d148@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/linux-f2fs-devel/0000000000005c7ccb061e032b9b@google.com
Fixes: 7950e9ac638e ("f2fs: stop gc/discard thread after fs shutdown")
Signed-off-by: Chao Yu <chao@kernel.org>
---
 fs/f2fs/file.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
index 7a37f2b393b9..62d72da25754 100644
--- a/fs/f2fs/file.c
+++ b/fs/f2fs/file.c
@@ -2388,7 +2388,10 @@ static int f2fs_ioc_shutdown(struct file *filp, unsigned long arg)
 		}
 	}
 
+	/* grab sb->s_umount to avoid racing w/ remount() */
+	down_read(&sbi->sb->s_umount);
 	ret = f2fs_do_shutdown(sbi, in, readonly);
+	up_read(&sbi->sb->s_umount);
 
 	if (need_drop)
 		mnt_drop_write_file(filp);
-- 
2.40.1
Re: [PATCH] f2fs: fix to avoid use-after-free in f2fs_stop_gc_thread()
Posted by Jaegeuk Kim 1 year, 6 months ago 
On 07/25, Chao Yu wrote:
> syzbot reports a f2fs bug as below:
> 
>  __dump_stack lib/dump_stack.c:88 [inline]
>  dump_stack_lvl+0x241/0x360 lib/dump_stack.c:114
>  print_report+0xe8/0x550 mm/kasan/report.c:491
>  kasan_report+0x143/0x180 mm/kasan/report.c:601
>  kasan_check_range+0x282/0x290 mm/kasan/generic.c:189
>  instrument_atomic_read_write include/linux/instrumented.h:96 [inline]
>  atomic_fetch_add_relaxed include/linux/atomic/atomic-instrumented.h:252 [inline]
>  __refcount_add include/linux/refcount.h:184 [inline]
>  __refcount_inc include/linux/refcount.h:241 [inline]
>  refcount_inc include/linux/refcount.h:258 [inline]
>  get_task_struct include/linux/sched/task.h:118 [inline]
>  kthread_stop+0xca/0x630 kernel/kthread.c:704
>  f2fs_stop_gc_thread+0x65/0xb0 fs/f2fs/gc.c:210
>  f2fs_do_shutdown+0x192/0x540 fs/f2fs/file.c:2283
>  f2fs_ioc_shutdown fs/f2fs/file.c:2325 [inline]
>  __f2fs_ioctl+0x443a/0xbe60 fs/f2fs/file.c:4325
>  vfs_ioctl fs/ioctl.c:51 [inline]
>  __do_sys_ioctl fs/ioctl.c:907 [inline]
>  __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:893
>  do_syscall_x64 arch/x86/entry/common.c:52 [inline]
>  do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> 
> The root cause is below race condition, it may cause use-after-free
> issue in sbi->gc_th pointer.
> 
> - remount
>  - f2fs_remount
>   - f2fs_stop_gc_thread
>    - kfree(gc_th)
> 				- f2fs_ioc_shutdown
> 				 - f2fs_do_shutdown
> 				  - f2fs_stop_gc_thread
> 				   - kthread_stop(gc_th->f2fs_gc_task)
> 
> We will call f2fs_do_shutdown() in two paths:
> - for f2fs_ioc_shutdown() path, we should grab sb->s_umount semaphore
> for fixing.
> - for f2fs_shutdown() path, it's safe since caller has already grabbed
> sb->s_umount semaphore.
> 
> Reported-by: syzbot+1a8e2b31f2ac9bd3d148@syzkaller.appspotmail.com
> Closes: https://lore.kernel.org/linux-f2fs-devel/0000000000005c7ccb061e032b9b@google.com
> Fixes: 7950e9ac638e ("f2fs: stop gc/discard thread after fs shutdown")
> Signed-off-by: Chao Yu <chao@kernel.org>
> ---
>  fs/f2fs/file.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
> index 7a37f2b393b9..62d72da25754 100644
> --- a/fs/f2fs/file.c
> +++ b/fs/f2fs/file.c
> @@ -2388,7 +2388,10 @@ static int f2fs_ioc_shutdown(struct file *filp, unsigned long arg)
>  		}
>  	}
>  
> +	/* grab sb->s_umount to avoid racing w/ remount() */
> +	down_read(&sbi->sb->s_umount);

Is this safe for freeze_bdev()?

>  	ret = f2fs_do_shutdown(sbi, in, readonly);
> +	up_read(&sbi->sb->s_umount);
>  
>  	if (need_drop)
>  		mnt_drop_write_file(filp);
> -- 
> 2.40.1
Re: [PATCH] f2fs: fix to avoid use-after-free in f2fs_stop_gc_thread()
Posted by Jaegeuk Kim 1 year, 6 months ago 
On 07/27, Jaegeuk Kim wrote:
> On 07/25, Chao Yu wrote:
> > syzbot reports a f2fs bug as below:
> > 
> >  __dump_stack lib/dump_stack.c:88 [inline]
> >  dump_stack_lvl+0x241/0x360 lib/dump_stack.c:114
> >  print_report+0xe8/0x550 mm/kasan/report.c:491
> >  kasan_report+0x143/0x180 mm/kasan/report.c:601
> >  kasan_check_range+0x282/0x290 mm/kasan/generic.c:189
> >  instrument_atomic_read_write include/linux/instrumented.h:96 [inline]
> >  atomic_fetch_add_relaxed include/linux/atomic/atomic-instrumented.h:252 [inline]
> >  __refcount_add include/linux/refcount.h:184 [inline]
> >  __refcount_inc include/linux/refcount.h:241 [inline]
> >  refcount_inc include/linux/refcount.h:258 [inline]
> >  get_task_struct include/linux/sched/task.h:118 [inline]
> >  kthread_stop+0xca/0x630 kernel/kthread.c:704
> >  f2fs_stop_gc_thread+0x65/0xb0 fs/f2fs/gc.c:210
> >  f2fs_do_shutdown+0x192/0x540 fs/f2fs/file.c:2283
> >  f2fs_ioc_shutdown fs/f2fs/file.c:2325 [inline]
> >  __f2fs_ioctl+0x443a/0xbe60 fs/f2fs/file.c:4325
> >  vfs_ioctl fs/ioctl.c:51 [inline]
> >  __do_sys_ioctl fs/ioctl.c:907 [inline]
> >  __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:893
> >  do_syscall_x64 arch/x86/entry/common.c:52 [inline]
> >  do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
> >  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> > 
> > The root cause is below race condition, it may cause use-after-free
> > issue in sbi->gc_th pointer.
> > 
> > - remount
> >  - f2fs_remount
> >   - f2fs_stop_gc_thread
> >    - kfree(gc_th)
> > 				- f2fs_ioc_shutdown
> > 				 - f2fs_do_shutdown
> > 				  - f2fs_stop_gc_thread
> > 				   - kthread_stop(gc_th->f2fs_gc_task)
> > 
> > We will call f2fs_do_shutdown() in two paths:
> > - for f2fs_ioc_shutdown() path, we should grab sb->s_umount semaphore
> > for fixing.
> > - for f2fs_shutdown() path, it's safe since caller has already grabbed
> > sb->s_umount semaphore.
> > 
> > Reported-by: syzbot+1a8e2b31f2ac9bd3d148@syzkaller.appspotmail.com
> > Closes: https://lore.kernel.org/linux-f2fs-devel/0000000000005c7ccb061e032b9b@google.com
> > Fixes: 7950e9ac638e ("f2fs: stop gc/discard thread after fs shutdown")
> > Signed-off-by: Chao Yu <chao@kernel.org>
> > ---
> >  fs/f2fs/file.c | 3 +++
> >  1 file changed, 3 insertions(+)
> > 
> > diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
> > index 7a37f2b393b9..62d72da25754 100644
> > --- a/fs/f2fs/file.c
> > +++ b/fs/f2fs/file.c
> > @@ -2388,7 +2388,10 @@ static int f2fs_ioc_shutdown(struct file *filp, unsigned long arg)
> >  		}
> >  	}
> >  
> > +	/* grab sb->s_umount to avoid racing w/ remount() */
> > +	down_read(&sbi->sb->s_umount);
> 
> Is this safe for freeze_bdev()?

bdev_freeze
 -> fs_bdev_freeze
  -> get_bdev_super
   -> bdev_super_lock(bdev, true)
    -> super_lock(sb, true)
     -> __super_lock(sb, true)
      -> down_write(s_umount)

> 
> >  	ret = f2fs_do_shutdown(sbi, in, readonly);
> > +	up_read(&sbi->sb->s_umount);
> >  
> >  	if (need_drop)
> >  		mnt_drop_write_file(filp);
> > -- 
> > 2.40.1
Re: [PATCH] f2fs: fix to avoid use-after-free in f2fs_stop_gc_thread()
Posted by Chao Yu 1 year, 6 months ago 
On 2024/7/27 23:27, Jaegeuk Kim wrote:
> On 07/27, Jaegeuk Kim wrote:
>> On 07/25, Chao Yu wrote:
>>> syzbot reports a f2fs bug as below:
>>>
>>>   __dump_stack lib/dump_stack.c:88 [inline]
>>>   dump_stack_lvl+0x241/0x360 lib/dump_stack.c:114
>>>   print_report+0xe8/0x550 mm/kasan/report.c:491
>>>   kasan_report+0x143/0x180 mm/kasan/report.c:601
>>>   kasan_check_range+0x282/0x290 mm/kasan/generic.c:189
>>>   instrument_atomic_read_write include/linux/instrumented.h:96 [inline]
>>>   atomic_fetch_add_relaxed include/linux/atomic/atomic-instrumented.h:252 [inline]
>>>   __refcount_add include/linux/refcount.h:184 [inline]
>>>   __refcount_inc include/linux/refcount.h:241 [inline]
>>>   refcount_inc include/linux/refcount.h:258 [inline]
>>>   get_task_struct include/linux/sched/task.h:118 [inline]
>>>   kthread_stop+0xca/0x630 kernel/kthread.c:704
>>>   f2fs_stop_gc_thread+0x65/0xb0 fs/f2fs/gc.c:210
>>>   f2fs_do_shutdown+0x192/0x540 fs/f2fs/file.c:2283
>>>   f2fs_ioc_shutdown fs/f2fs/file.c:2325 [inline]
>>>   __f2fs_ioctl+0x443a/0xbe60 fs/f2fs/file.c:4325
>>>   vfs_ioctl fs/ioctl.c:51 [inline]
>>>   __do_sys_ioctl fs/ioctl.c:907 [inline]
>>>   __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:893
>>>   do_syscall_x64 arch/x86/entry/common.c:52 [inline]
>>>   do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
>>>   entry_SYSCALL_64_after_hwframe+0x77/0x7f
>>>
>>> The root cause is below race condition, it may cause use-after-free
>>> issue in sbi->gc_th pointer.
>>>
>>> - remount
>>>   - f2fs_remount
>>>    - f2fs_stop_gc_thread
>>>     - kfree(gc_th)
>>> 				- f2fs_ioc_shutdown
>>> 				 - f2fs_do_shutdown
>>> 				  - f2fs_stop_gc_thread
>>> 				   - kthread_stop(gc_th->f2fs_gc_task)
>>>
>>> We will call f2fs_do_shutdown() in two paths:
>>> - for f2fs_ioc_shutdown() path, we should grab sb->s_umount semaphore
>>> for fixing.
>>> - for f2fs_shutdown() path, it's safe since caller has already grabbed
>>> sb->s_umount semaphore.
>>>
>>> Reported-by: syzbot+1a8e2b31f2ac9bd3d148@syzkaller.appspotmail.com
>>> Closes: https://lore.kernel.org/linux-f2fs-devel/0000000000005c7ccb061e032b9b@google.com
>>> Fixes: 7950e9ac638e ("f2fs: stop gc/discard thread after fs shutdown")
>>> Signed-off-by: Chao Yu <chao@kernel.org>
>>> ---
>>>   fs/f2fs/file.c | 3 +++
>>>   1 file changed, 3 insertions(+)
>>>
>>> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
>>> index 7a37f2b393b9..62d72da25754 100644
>>> --- a/fs/f2fs/file.c
>>> +++ b/fs/f2fs/file.c
>>> @@ -2388,7 +2388,10 @@ static int f2fs_ioc_shutdown(struct file *filp, unsigned long arg)
>>>   		}
>>>   	}
>>>   
>>> +	/* grab sb->s_umount to avoid racing w/ remount() */
>>> +	down_read(&sbi->sb->s_umount);
>>
>> Is this safe for freeze_bdev()?
> 
> bdev_freeze
>   -> fs_bdev_freeze
>    -> get_bdev_super
>     -> bdev_super_lock(bdev, true)
>      -> super_lock(sb, true)
>       -> __super_lock(sb, true)
>        -> down_write(s_umount)

Oops, let me check this.

Thanks,

> 
>>
>>>   	ret = f2fs_do_shutdown(sbi, in, readonly);
>>> +	up_read(&sbi->sb->s_umount);
>>>   
>>>   	if (need_drop)
>>>   		mnt_drop_write_file(filp);
>>> -- 
>>> 2.40.1

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