Hi Chen Zhongjin, On Sat, Nov 19, 2022 at 2:29 PM Chen Zhongjin wrote: > > > On 2022/11/19 13:24, Chen Zhongjin wrote: > > On 2022/11/19 6:11, Andrew Morton wrote: > >> 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! > > > > Yes, seems it is introduced at the beginning of this file and the > > function called nilfs_touch_segusage(). > > Could you please resubmit the patch reflecting the following comments ? After I replied to Andrew, I noticed them. Also, When reposting, it would be helpful if you could add all the tags I asked for Andrew in advance. Comments: 1) Please change nilfs_sufile_mark_dirty() so that it protects the segusage modification with &NILFS_MDT(sufile)->mi_sem: > --- 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); + down_write(&NILFS_MDT(sufile)->mi_sem); > 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; All functions that modify metadata on the sufile need protection with this R/W semaphore. You may not see this protection for some sufile functions as is, but in that case, the wrapper function that uses them acquires this R/W semaphore instead. Since I retested for this change as well, you don't have to drop my "Tested-by" tag. 2) Please use the following complete email address for the "Reported-by" tag of syzbot. Reported-by: syzbot+77e4f005cb899d4268d1@xxxxxxxxxxxxxxxxxxxxxxxxx Your tag is partially abbreviated. I don't know that abbreviation is valid, but there are very few examples of such. And even if it's valid for syzbot, I don't think that omission is desirable as some tools may not support it. Thanks, Ryusuke Konishi
