linux-kernel - Re: [PATCH v2] f2fs: compress: fix UAF of f2fs_inode_info in f2fs_free

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Message-ID: <CAHJ8P3JcGAtwQVTqCfno+_agZjkEMn3XHtgBeOicUAPkONvnTQ@mail.gmail.com>
Date: Thu, 5 Jun 2025 12:05:17 +0800
From: Zhiguo Niu <niuzhiguo84@...il.com>
To: Chao Yu <chao@...nel.org>
Cc: Zhiguo Niu <zhiguo.niu@...soc.com>, jaegeuk@...nel.org, 
	linux-f2fs-devel@...ts.sourceforge.net, linux-kernel@...r.kernel.org, 
	ke.wang@...soc.com, Hao_hao.Wang@...soc.com, baocong.liu@...soc.com
Subject: Re: [PATCH v2] f2fs: compress: fix UAF of f2fs_inode_info in f2fs_free_dic

Chao Yu <chao@...nel.org> 于2025年6月5日周四 11:31写道：
>
> On 6/5/25 10:44, Zhiguo Niu wrote:
> > Chao Yu <chao@...nel.org> 于2025年6月5日周四 10:23写道：
> >>
> >> On 6/4/25 19:37, 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 __iget before f2fs_free_dic and iput after free the dic.
> >>>
> >>> Cc: Daeho Jeong <daehojeong@...gle.com>
> >>> Fixes: bff139b49d9f ("f2fs: handle decompress only post processing in softirq")
> >>> Signed-off-by: Zhiguo Niu <zhiguo.niu@...soc.com>
> >>> Signed-off-by: Baocong Liu <baocong.liu@...soc.com>
> >>> ---
> >>> v2: use __iget/iput function
> >>> ---
> >>>  fs/f2fs/compress.c | 16 +++++++++++-----
> >>>  1 file changed, 11 insertions(+), 5 deletions(-)
> >>>
> >>> diff --git a/fs/f2fs/compress.c b/fs/f2fs/compress.c
> >>> index b3c1df9..3f0c18d 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 +1785,20 @@ 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);
> >>> +                     /* to avoid inode is evicted simultaneously */
> >>> +                     spin_lock(&dic->inode->i_lock);
> >>> +                     __iget(dic->inode);
> >>> +                     spin_unlock(&dic->inode->i_lock);
> >>
> >> Oh, how about using igrab() instead?
> > Hi Chao,
> > after I check igrab, I think it is ok,
> > but here We don't need care about igarb's return value, right?
>
> I guess "return NULL" should be impossible case, but still we can add
> f2fs_bug_on() to detect any potential bug, right?
OK, thanks for your suggestions.
>
> Thanks,
>
> > Thanks!
> >
> >>
> >>>                       queue_work(F2FS_I_SB(dic->inode)->post_read_wq,
> >>>                                       &dic->free_work);
> >>>               }
> >>
>