Re: [PATCH V3] bcachefs: Add journal v2 entry nr value check

[Lizhi Xu]

On Tue, 20 Aug 2024 23:00:05 -0400, Kent Overstreet wrote:
> > When the nr value of a signle entry or their sum overflows, it will
> > cause the value of ja->nr to be incorrect, this will result in the
> > allocated memory to ja->buckets being too small, leading to out of
> > bounds access in bch2_dev_journal_init.
> > 
> > Reported-by: syzbot+47ecc948aadfb2ab3efc@xxxxxxxxxxxxxxxxxxxxxxxxx
> > Signed-off-by: Lizhi Xu <lizhi.xu@xxxxxxxxxxxxx>
> > ---
> >  fs/bcachefs/journal_sb.c | 16 +++++++++++++++-
> >  1 file changed, 15 insertions(+), 1 deletion(-)
> > 
> > diff --git a/fs/bcachefs/journal_sb.c b/fs/bcachefs/journal_sb.c
> > index db80e506e3ab..230ed99130e4 100644
> > --- a/fs/bcachefs/journal_sb.c
> > +++ b/fs/bcachefs/journal_sb.c
> > @@ -107,6 +107,7 @@ static int bch2_sb_journal_v2_validate(struct bch_sb *sb, struct bch_sb_field *f
> >  	unsigned nr;
> >  	unsigned i;
> >  	struct u64_range *b;
> > +	u64 total_nr = 0, entry_nr;
> >  
> >  	nr = bch2_sb_field_journal_v2_nr_entries(journal);
> >  	if (!nr)
> > @@ -117,8 +118,21 @@ static int bch2_sb_journal_v2_validate(struct bch_sb *sb, struct bch_sb_field *f
> >  		return -BCH_ERR_ENOMEM_sb_journal_v2_validate;
> >  
> >  	for (i = 0; i < nr; i++) {
> > +		entry_nr = le64_to_cpu(journal->d[i].nr);
> > +		if (entry_nr > UINT_MAX) {
> > +			prt_printf(err, "Journal v2 entry d[%u] nr %llu overflow\n",
> > +				i, entry_nr);
> > +			goto err;
> > +		}
> 
> This check is unnecessary; we know the sum can't overflow a u64 because
> we're also checking that the entries are nonoverlapping.
You didn't read my previous email carefully.
In this issue, journal->d[0] is 7, journal->d[1] is 18446744073709551615,
so the sum of their u64 type values will definitely overflow.
> 
> > +		total_nr += entry_nr;
> >  		b[i].start = le64_to_cpu(journal->d[i].start);
> > -		b[i].end = b[i].start + le64_to_cpu(journal->d[i].nr);
> > +		b[i].end = b[i].start + entry_nr;
> > +	}
> > +
> > +	if (total_nr > UINT_MAX) {
> > +		prt_printf(err, "Sum of journal v2 entries nr %llu overflow\n",
> > +				total_nr);
> > +		goto err;
> >  	}
> >  
> >  	sort(b, nr, sizeof(*b), u64_range_cmp, NULL);
> > -- 

BR,
Lizhi