linux-kernel - Re: [PATCH v2] f2fs: avoid out-of-range memory access

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Date:   Wed, 3 Jul 2019 23:03:55 +0800
From:   Ocean Chen <oceanchen@...gle.com>
To:     yuchao0@...wei.com, jaegeuk@...nel.org,
        linux-f2fs-devel@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] f2fs: avoid out-of-range memory access

Hi Yu Chao,

The cur_data_segno only was checked in mount process. In terms of
security concern, it's better to check value before using it. I know the
risk is low. IMHO, it can be safer.
BTW, I found we can only check blk_off before for loop instead of
checking 'j' in each iteratoin.

On Wed, Jul 03, 2019 at 10:07:11AM +0800, Chao Yu wrote:
> Hi Ocean,
> 
> If filesystem is corrupted, it should fail mount due to below check in
> f2fs_sanity_check_ckpt(), so we are safe in read_compacted_summaries() to access
> entries[0,blk_off], right?
> 
> 	for (i = 0; i < NR_CURSEG_DATA_TYPE; i++) {
> 		if (le32_to_cpu(ckpt->cur_data_segno[i]) >= main_segs ||
> 			le16_to_cpu(ckpt->cur_data_blkoff[i]) >= blocks_per_seg)
> 			return 1;
> 
> Thanks,
> 
> On 2019/7/2 16:05, Ocean Chen wrote:
> > blk_off might over 512 due to fs corrupt.
> > Use ENTRIES_IN_SUM to protect invalid memory access.
> > 
> > v2:
> > - fix typo
> > Signed-off-by: Ocean Chen <oceanchen@...gle.com>
> > ---
> >  fs/f2fs/segment.c | 2 ++
> >  1 file changed, 2 insertions(+)
> > 
> > diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> > index 8dee063c833f..a5e8af0bd62e 100644
> > --- a/fs/f2fs/segment.c
> > +++ b/fs/f2fs/segment.c
> > @@ -3403,6 +3403,8 @@ static int read_compacted_summaries(struct f2fs_sb_info *sbi)
> >  
> >  		for (j = 0; j < blk_off; j++) {
> >  			struct f2fs_summary *s;
> > +			if (j >= ENTRIES_IN_SUM)
> > +				return -EFAULT;
> >  			s = (struct f2fs_summary *)(kaddr + offset);
> >  			seg_i->sum_blk->entries[j] = *s;
> >  			offset += SUMMARY_SIZE;
> >