Chao Yu <c...@kernel.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 <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?
OK, thanks for your suggestions.
>
> Thanks,
>
> > Thanks!
> >
> >>
> >>> queue_work(F2FS_I_SB(dic->inode)->post_read_wq,
> >>> &dic->free_work);
> >>> }
> >>
>
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