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=c7c4748e11ffcc367cef04f76e02e931833cbd2...
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.
Fix this by setting usage as dirty in nilfs_sufile_mark_dirty(), and add lock in it to protect the usage modification.
Fixes: 9ff05123e3bf ("nilfs2: segment constructor") Cc: stable@vger.kernel.org Reported-by: syzbot+77e4f005cb899d4268d1@syzkaller.appspotmail.com Reported-by: Liu Shixin liushixin2@huawei.com Signed-off-by: Chen Zhongjin chenzhongjin@huawei.com Acked-by: Ryusuke Konishi konishi.ryusuke@gmail.com Tested-by: Ryusuke Konishi konishi.ryusuke@gmail.com --- v1 -> v2: 1) Add lock protection as Ryusuke suggested and slightly fix commit message. 2) Fix and add tags. --- 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; }