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?
> queue_work(F2FS_I_SB(dic->inode)->post_read_wq,
> &dic->free_work);
> }
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