linux-kernel - Re: [PATCH v3] f2fs: compress: fix UAF of f2fs_inode_info in f2fs_free

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Message-ID: <CAHJ8P3LNrSRT8hfbr=x5HvkQRGBSTpftPbd7NrfUdO-2LgSLfg@mail.gmail.com>
Date: Wed, 11 Jun 2025 14:41:42 +0800
From: Zhiguo Niu <niuzhiguo84@...il.com>
To: Chao Yu <chao@...nel.org>
Cc: Jaegeuk Kim <jaegeuk@...nel.org>, Zhiguo Niu <zhiguo.niu@...soc.com>, 
	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 v3] f2fs: compress: fix UAF of f2fs_inode_info in f2fs_free_dic

Chao Yu <chao@...nel.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?"
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@...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>
> >> ---
> >> 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
>