linux-kernel - Re: [PATCH V2] bcachefs: Add journal v2 entry nr value check

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Message-ID: <20240821023355.1619187-1-lizhi.xu@windriver.com>
Date: Wed, 21 Aug 2024 10:33:55 +0800
From: Lizhi Xu <lizhi.xu@...driver.com>
To: <kent.overstreet@...ux.dev>
CC: <linux-bcachefs@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <lizhi.xu@...driver.com>,
        <syzbot+47ecc948aadfb2ab3efc@...kaller.appspotmail.com>,
        <syzkaller-bugs@...glegroups.com>
Subject: Re: [PATCH V2] bcachefs: Add journal v2 entry nr value check

On Tue, 20 Aug 2024 19:34:18 -0400, Kent Overstreet wrote:
> > When journal v2 entry nr overflow, 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@...kaller.appspotmail.com
> > Signed-off-by: Lizhi Xu <lizhi.xu@...driver.com>
> > ---
> >  fs/bcachefs/journal_sb.c | 5 +++++
> >  1 file changed, 5 insertions(+)
> >
> > diff --git a/fs/bcachefs/journal_sb.c b/fs/bcachefs/journal_sb.c
> > index db80e506e3ab..db2b2100e4e5 100644
> > --- a/fs/bcachefs/journal_sb.c
> > +++ b/fs/bcachefs/journal_sb.c
> > @@ -119,6 +119,11 @@ static int bch2_sb_journal_v2_validate(struct bch_sb *sb, struct bch_sb_field *f
> >  	for (i = 0; i < nr; i++) {
> >  		b[i].start = le64_to_cpu(journal->d[i].start);
> >  		b[i].end = b[i].start + le64_to_cpu(journal->d[i].nr);
> > +		if (le64_to_cpu(journal->d[i].nr) > UINT_MAX) {
> > +			prt_printf(err, "journal v2 entry d[%u].nr %llu overflow\n",
> > +				i, le64_to_cpu(journal->d[i].nr));
> > +			goto err;
> > +		}
> 
> no, you need to sum up _all_ the entries and verify the total doesn't
> overflow UINT_MAX
The overflow value of le64_to_cpu(journal->d[i].nr) is 18446744073709551615(for u64),
or in other words, it is -1 for s64.

Therefore, the existing check for single entry is retained, and an overflow
check for the total value of all entry is will added.

BR,
Lizhi