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Message-ID: <c36ab955-c8db-4a8b-a9d0-f07b5f426c3f@kernel.org>
Date: Wed, 11 Jun 2025 14:47:14 +0800
From: Chao Yu <chao@...nel.org>
To: Zhiguo Niu <niuzhiguo84@...il.com>
Cc: chao@...nel.org, 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
On 6/11/25 14:41, Zhiguo Niu wrote:
> 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?"
Zhiguo,
Yeah, I guess so.
Thanks,
> 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
>>
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