Re: [PATCH] nilfs2: Fix nilfs_sufile_mark_dirty() not set segment usage as dirty

[Andrew Morton <akpm@linux-foundation.org>]

On Fri, 18 Nov 2022 14:33:04 +0800 Chen Zhongjin <chenzhongjin@huawei.com> wrote:

> In nilfs_sufile_mark_dirty(), the buffer and inode are set dirty, but
> nilfs_segment_usage is not set dirty, which makes it can be found by
> nilfs_sufile_alloc() because it checks nilfs_segment_usage_clean(su).
> 
> This will cause the problem reported by syzkaller:
> https://syzkaller.appspot.com/bug?id=c7c4748e11ffcc367cef04f76e02e931833cbd24
> 
> It's because the case starts with segbuf1.segnum = 3, nextnum = 4, and
> nilfs_sufile_alloc() not called to allocate a new segment.
> 
> The first time nilfs_segctor_extend_segments() allocated segment
> segbuf2.segnum = segbuf1.nextnum = 4, then nilfs_sufile_alloc() found
> nextnextnum = 4 segment because its su is not set dirty.
> So segbuf2.nextnum = 4, which causes next segbuf3.segnum = 4.
> 
> sb_getblk() will get same bh for segbuf2 and segbuf3, and this bh is
> added to both buffer lists of two segbuf.
> It makes the list head of second list linked to the first one. When
> iterating the first one, it will access and deref the head of second,
> which causes NULL pointer dereference.
> 
> Fixes: 9ff05123e3bf ("nilfs2: segment constructor")

Merged in 2009!

> --- a/fs/nilfs2/sufile.c
> +++ b/fs/nilfs2/sufile.c
> @@ -495,12 +495,18 @@ void nilfs_sufile_do_free(struct inode *sufile, __u64 segnum,
>  int nilfs_sufile_mark_dirty(struct inode *sufile, __u64 segnum)
>  {
>  	struct buffer_head *bh;
> +	void *kaddr;
> +	struct nilfs_segment_usage *su;
>  	int ret;
>  
>  	ret = nilfs_sufile_get_segment_usage_block(sufile, segnum, 0, &bh);
>  	if (!ret) {
>  		mark_buffer_dirty(bh);
>  		nilfs_mdt_mark_dirty(sufile);
> +		kaddr = kmap_atomic(bh->b_page);
> +		su = nilfs_sufile_block_get_segment_usage(sufile, segnum, bh, kaddr);
> +		nilfs_segment_usage_set_dirty(su);
> +		kunmap_atomic(kaddr);
>  		brelse(bh);
>  	}
>  	return ret;

Do we feel that this fix should be backported into -stable kernels?