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: stable@xxxxxxxxxxxxxxx Reported-by: syzbot+77e4f005cb899d4268d1@xxxxxxxxxxxxxxxxxxxxxxxxx Reported-by: Liu Shixin <liushixin2@xxxxxxxxxx> Signed-off-by: Chen Zhongjin <chenzhongjin@xxxxxxxxxx> Acked-by: Ryusuke Konishi <konishi.ryusuke@xxxxxxxxx> Tested-by: Ryusuke Konishi <konishi.ryusuke@xxxxxxxxx> --- 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. --- 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
