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Message-ID: <CAHJ8P3JCV9wjRXC530WgPjZx-_XEhVRoG3B9Mcn4XG_Y-x1nGQ@mail.gmail.com>
Date: Wed, 4 Jun 2025 19:14:31 +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] f2fs: compress: fix UAF of f2fs_inode_info in f2fs_free_dic
Chao Yu <chao@...nel.org> 于2025年6月4日周三 19:09写道：
>
> On 6/4/25 18:49, Zhiguo Niu wrote:
> > Chao Yu <chao@...nel.org> 于2025年6月4日周三 17:48写道：
> >>
> >> On 6/4/25 13:54, 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 increase inode->i_count before f2fs_free_dic and decrease it
> >>> 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>
> >>> ---
> >>> fs/f2fs/compress.c | 19 ++++++++++++++-----
> >>> 1 file changed, 14 insertions(+), 5 deletions(-)
> >>>
> >>> diff --git a/fs/f2fs/compress.c b/fs/f2fs/compress.c
> >>> index b3c1df9..6b3b3a7 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 +1775,11 @@ static void f2fs_free_dic(struct decompress_io_ctx *dic,
> >>> }
> >>>
> >>> page_array_free(dic->inode, dic->rpages, dic->nr_rpages);
> >>> + if (late_free) {
> >>> + spin_lock(&dic->inode->i_lock);
> >>> + atomic_dec(&dic->inode->i_count);
> >>> + spin_unlock(&dic->inode->i_lock);
> >>
> >> If it is the last one release i_count, it needs to call iput_final to evict inode
> >> like what iput did, so we'd better to call iput() here?
> > Hi Chao,
> > Yes, we have also tested this method(iput/__iget), and it worked.
> > Just think It is simpler and easier to read to directly operate
> > i_count, and then free it
> > by relying on the memory module when i_count=0.
> > But It seems iput/__iget is better.
> >>
> >>> + }
> >>> kmem_cache_free(dic_entry_slab, dic);
> >>> }
> >>>
> >>> @@ -1783,16 +1788,20 @@ 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);
> >>> + atomic_inc(&dic->inode->i_count);
> >>> + spin_unlock(&dic->inode->i_lock);
> >>
> >> iget()?
> >>
> >> BTW, can we store i_compress_algorithm in dic to avoid inode access?
> >
> > Also thought of this method, but it would require more changes.
> > dic->inode used in f2fs_free_dic are all needed to modify except
> > i_compress_algorithm.
> > such as page_array_free(dic->inode),
>
> Zhiguo,
>
> page_array_free() parses dic->inode to get sbi only, so we can pass sbi to
> page_array_free() directly to avoid using dic->inode.
Hi Chao,
but now sbi is not in dic structure, so we also need to add it ?
>
> > allow_memalloc_for_decomp(F2FS_I_SB(dic->inode)).
> >
> > Do you have any other suggestions?
>
> Using iget/iput looks fine to me, please go ahead.
OK~
thanks!
>
> Thanks,
>
> > thanks！
> >
> >>
> >> Thanks,
> >>
> >>> queue_work(F2FS_I_SB(dic->inode)->post_read_wq,
> >>> &dic->free_work);
> >>> }
> >>
>
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