On Sat, Nov 19, 2022 at 4:17 PM Ryusuke Konishi wrote: > > 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); Sorry, the location of this down_write() was wrong in this email. In my tested change, I put it before nilfs_sufile_get_segment_usage_block() like others. > + 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; > > 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. Regards, Ryusuke Konishi > > 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
