On Fri, 18 Nov 2022 14:33:04 +0800 Chen Zhongjin <chenzhongjin@xxxxxxxxxx> 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?
