Re: [PATCH 2/2] f2fs: compress: fix UAF of f2fs_inode_info in f2fs_free_dic

[Chao Yu <chao@kernel.org>]

On 2025/6/13 9:50, 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 store compress_algorithm and sbi in dic to avoid inode UAF.
> 
> In addition, the previous solution is deprecated in [1] may cause system hang.
> [1] https://lore.kernel.org/all/c36ab955-c8db-4a8b-a9d0-f07b5f426c3f@kernel.org
> 
> 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,