Re: [PATCH v3] f2fs: compress: fix UAF of f2fs_inode_info in f2fs_free_dic

[Chao Yu <chao@kernel.org>]

On 6/11/25 14:41, Zhiguo Niu wrote:
> Chao Yu <chao@kernel.org> 于2025年6月11日周三 14:07写道：
>>
>> On 6/11/25 00:08, Jaegeuk Kim wrote:
>>> Hi Zhiguo,
>>>
>>> This patch causes CPU hang when running fsstress on compressed/non-compressed
>>> files. Please check.
>>
>> Oh, seems it may cause below deadlock:
>>
>> CPU0
>> process A
>> - spin_lock(i_lock)
>> software IRQ
>> - end_io
>>  - igrab
>>   - spin_lock(i_lock)
>>
>> Thanks,
> Hi Chao,
> Thanks for pointing this out.
> I have tested this patch locally about some basic cases before submission.
> So it seems that should use the following method  to solve this problem?
> " store i_compress_algorithm/sbi in dic to avoid inode access?"

Zhiguo,

Yeah, I guess so.

Thanks,

> thanks！
> 
> 
>>
>>>
>>> On 06/05, Zhiguo Niu wrote:
>>>> The decompress_io_ctx may be released asynchronously after
>>>> I/O completion. If this file is deleted immediately after read,
>>>> and the kworker of processing post_read_wq has not been executed yet
>>>> due to high workloads, It is possible that the inode(f2fs_inode_info)
>>>> is evicted and freed before it is used f2fs_free_dic.
>>>>
>>>>     The UAF case as below:
>>>>     Thread A                                      Thread B
>>>>     - f2fs_decompress_end_io
>>>>      - f2fs_put_dic
>>>>       - queue_work
>>>>         add free_dic work to post_read_wq
>>>>                                                    - do_unlink
>>>>                                                     - iput
>>>>                                                      - evict
>>>>                                                       - call_rcu
>>>>     This file is deleted after read.
>>>>
>>>>     Thread C                                 kworker to process post_read_wq
>>>>     - rcu_do_batch
>>>>      - f2fs_free_inode
>>>>       - kmem_cache_free
>>>>      inode is freed by rcu
>>>>                                              - process_scheduled_works
>>>>                                               - f2fs_late_free_dic
>>>>                                                - f2fs_free_dic
>>>>                                                 - f2fs_release_decomp_mem
>>>>                                       read (dic->inode)->i_compress_algorithm
>>>>
>>>> This patch use igrab before f2fs_free_dic and iput after free the dic when dic free
>>>> action is done by kworker.
>>>>
>>>> Cc: Daeho Jeong <daehojeong@google.com>
>>>> Fixes: bff139b49d9f ("f2fs: handle decompress only post processing in softirq")
>>>> Signed-off-by: Zhiguo Niu <zhiguo.niu@unisoc.com>
>>>> Signed-off-by: Baocong Liu <baocong.liu@unisoc.com>
>>>> ---
>>>> v3: use igrab to replace __iget
>>>> v2: use __iget/iput function
>>>> ---
>>>>  fs/f2fs/compress.c | 14 +++++++++-----
>>>>  1 file changed, 9 insertions(+), 5 deletions(-)
>>>>
>>>> diff --git a/fs/f2fs/compress.c b/fs/f2fs/compress.c
>>>> index b3c1df9..729ad16 100644
>>>> --- a/fs/f2fs/compress.c
>>>> +++ b/fs/f2fs/compress.c
>>>> @@ -1687,7 +1687,7 @@ static void f2fs_release_decomp_mem(struct decompress_io_ctx *dic,
>>>>  }
>>>>
>>>>  static void f2fs_free_dic(struct decompress_io_ctx *dic,
>>>> -            bool bypass_destroy_callback);
>>>> +            bool bypass_destroy_callback, bool late_free);
>>>>
>>>>  struct decompress_io_ctx *f2fs_alloc_dic(struct compress_ctx *cc)
>>>>  {
>>>> @@ -1743,12 +1743,12 @@ struct decompress_io_ctx *f2fs_alloc_dic(struct compress_ctx *cc)
>>>>      return dic;
>>>>
>>>>  out_free:
>>>> -    f2fs_free_dic(dic, true);
>>>> +    f2fs_free_dic(dic, true, false);
>>>>      return ERR_PTR(ret);
>>>>  }
>>>>
>>>>  static void f2fs_free_dic(struct decompress_io_ctx *dic,
>>>> -            bool bypass_destroy_callback)
>>>> +            bool bypass_destroy_callback, bool late_free)
>>>>  {
>>>>      int i;
>>>>
>>>> @@ -1775,6 +1775,8 @@ static void f2fs_free_dic(struct decompress_io_ctx *dic,
>>>>      }
>>>>
>>>>      page_array_free(dic->inode, dic->rpages, dic->nr_rpages);
>>>> +    if (late_free)
>>>> +            iput(dic->inode);
>>>>      kmem_cache_free(dic_entry_slab, dic);
>>>>  }
>>>>
>>>> @@ -1783,16 +1785,18 @@ static void f2fs_late_free_dic(struct work_struct *work)
>>>>      struct decompress_io_ctx *dic =
>>>>              container_of(work, struct decompress_io_ctx, free_work);
>>>>
>>>> -    f2fs_free_dic(dic, false);
>>>> +    f2fs_free_dic(dic, false, true);
>>>>  }
>>>>
>>>>  static void f2fs_put_dic(struct decompress_io_ctx *dic, bool in_task)
>>>>  {
>>>>      if (refcount_dec_and_test(&dic->refcnt)) {
>>>>              if (in_task) {
>>>> -                    f2fs_free_dic(dic, false);
>>>> +                    f2fs_free_dic(dic, false, false);
>>>>              } else {
>>>>                      INIT_WORK(&dic->free_work, f2fs_late_free_dic);
>>>> +                    /* use igrab to avoid inode is evicted simultaneously */
>>>> +                    f2fs_bug_on(F2FS_I_SB(dic->inode), !igrab(dic->inode));
>>>>                      queue_work(F2FS_I_SB(dic->inode)->post_read_wq,
>>>>                                      &dic->free_work);
>>>>              }
>>>> --
>>>> 1.9.1
>>