On 6/5/25 10:44, Zhiguo Niu wrote:
> Chao Yu <c...@kernel.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 <daehoje...@google.com>
>>> Fixes: bff139b49d9f ("f2fs: handle decompress only post processing in
>>> softirq")
>>> Signed-off-by: Zhiguo Niu <zhiguo....@unisoc.com>
>>> Signed-off-by: Baocong Liu <baocong....@unisoc.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?
Thanks,
> Thanks!
>
>>
>>> queue_work(F2FS_I_SB(dic->inode)->post_read_wq,
>>> &dic->free_work);
>>> }
>>
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