Messages in this thread |  | | Date | Mon, 21 Nov 2022 10:16:41 +0800 | Subject | Re: [PATCH v2] nilfs2: Fix nilfs_sufile_mark_dirty() not set segment usage as dirty | From | Chen Zhongjin <> |
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Hi,
On 2022/11/19 22:09, Ryusuke Konishi wrote: > On Sat, Nov 19, 2022 at 6:37 PM Chen Zhongjin 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). > The body of the patch looks OK, but this part of the commit log is a > bit misleading. > Could you please modify the expression so that we can understand this > patch fixes the issue when the disk image is corrupted and the leak > wasn't always there ?
Makes sense. I'm going to fix the message as this:
When extending segment, the current segment is allocated and set dirty by previous nilfs_sufile_alloc(). But for some special cases such as corrupted image it can be unreliable, so nilfs_sufile_mark_dirty() is called to promise that current segment is dirty.
However, nilfs_sufile_mark_dirty() only sets buffer and inode dirty while nilfs_segment_usage can still be clean an used by following nilfs_sufile_alloc() because it checks nilfs_segment_usage_clean(su).
This will cause the problem reported...
Could you please have a check? Thanks!
Best, Chen > Originally, the assumption was that the current and next segments > pointed to by log headers had been made dirty, and in fact mkfs.nilfs2 > and nilfs2 itself had created metadata that way, so it wasn't really a > problem. Usually the segment usage that this patch tries to dirty is > already marked dirty and usually results in duplicate processing. > nilfs_sufile_mark_dirty() is really only supposed to dirty that buffer > and inode, and this patch changes the role. > > However, that assumption was incomplete in the sense that it does not > assume broken metadata (whether intentionally or as a result of > device/media failure), and lacked checks or protection from it. In > the meantime, you showed the simple and safe workaround even though it > duplicates in almost all cases and even changes the semantics of the > function. > In terms of the stability and safety, your patch is good that we can > ignore the inefficiency, so I am pushing for this change. > > Thanks, > Ryusuke Konishi > >> 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. >> >> 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; >> } >> >> -- >> 2.17.1 >>
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