Messages in this thread | | | Date | Sat, 19 Nov 2022 13:28:53 +0800 | Subject | Re: [PATCH] nilfs2: Fix nilfs_sufile_mark_dirty() not set segment usage as dirty | From | Chen Zhongjin <> |
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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@huawei.com> 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(). > > Wired that this problem is not discovered utill now. So I'm wondering > that whether this is a real-world > problem or just a use case constructed maliciously by syzkaller. But > according to the result of syzkaller bisection, > this problem should have a history. >>> --- 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? > Sorry that I'm not familiar with the specific use scenarios of nilfs2. > So I can't offer a better advice. I think if it > is a problem that not happen easily in normal situations there's no > necessary to backport it to stable.
I just noticed Ryusuke's mail so let's do it as his advice.
Thanks for your time!
Best,
Chen
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