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

[Chao Yu <chao@kernel.org>]

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,

> 
> 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