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

[Chao Yu <chao@kernel.org>]

On 6/5/25 15:18, 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>

Reviewed-by: Chao Yu <chao@kernel.org>

Thanks,