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

Ocean Chen
2019-07-03T15:04:05Z

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@google.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;
> >