On Mon, Nov 21, 2022 at 6:14 PM Chen Zhongjin wrote:
>
> When extending segments, nilfs_sufile_alloc() is called to get an
> unassigned segment, then mark it as dirty to avoid accidentally
> allocating the same segment in the future.
>
> But for some special cases such as a corrupted image it can be
> unreliable.
> If such corruption of the dirty state of the segment occurs, nilfs2 may
> reallocate a segment that is in use and pick the same segment for
> writing twice at the same time.
>
> This will cause the problem reported by syzkaller:
> https://syzkaller.appspot.com/bug?id=c7c4748e11ffcc367cef04f76e02e931833cbd24
>
> This case started with segbuf1.segnum = 3, nextnum = 4 when constructed.
> It supposed segment 4 has already been allocated and marked as dirty.
>
> However the dirty state was corrupted and segment 4 usage was not dirty.
> For the first time nilfs_segctor_extend_segments() segment 4 was
> allocated again, which made segbuf2 and next segbuf3 had same segment 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 lists broken
> which causes NULL pointer dereference.
>
> Fix the problem by setting usage as dirty every time in
> nilfs_sufile_mark_dirty(), which is called during constructing current
> segment to be written out and before allocating next segment.
>
> Fixes: 9ff05123e3bf ("nilfs2: segment constructor")
> Cc: [email protected]
> Reported-by: [email protected]
> Reported-by: Liu Shixin <[email protected]>
> Signed-off-by: Chen Zhongjin <[email protected]>
> Acked-by: Ryusuke Konishi <[email protected]>
> Tested-by: Ryusuke Konishi <[email protected]>
> ---
> v1 -> v2:
> 1) Add lock protection as Ryusuke suggested and slightly fix commit
> message.
> 2) Fix and add tags.
>
> v2 -> v3:
> Fix commit message to make it clear.
Looks good to me.
Andrew, could you please apply this patch instead of the currently queued patch?
Thanks,
Ryusuke Konishi
> ---
> fs/nilfs2/sufile.c | 8 ++++++++
> 1 file changed, 8 insertions(+)
>
> diff --git a/fs/nilfs2/sufile.c b/fs/nilfs2/sufile.c
> index 77ff8e95421f..dc359b56fdfa 100644
> --- a/fs/nilfs2/sufile.c
> +++ b/fs/nilfs2/sufile.c
> @@ -495,14 +495,22 @@ 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;
>
> + down_write(&NILFS_MDT(sufile)->mi_sem);
> 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);
> }
> + up_write(&NILFS_MDT(sufile)->mi_sem);
> return ret;
> }
>
> --
> 2.17.1
>