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

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Message-ID: <zdrkmfo2ln2t7e3oh3mz3yr2xs67qm3ea4wfe4fnv6zw4fk4pd@k5peuzfz5ods>
Date: Tue, 20 Aug 2024 23:00:05 -0400
From: Kent Overstreet <kent.overstreet@...ux.dev>
To: Lizhi Xu <lizhi.xu@...driver.com>
Cc: linux-bcachefs@...r.kernel.org, linux-kernel@...r.kernel.org, 
	syzbot+47ecc948aadfb2ab3efc@...kaller.appspotmail.com, syzkaller-bugs@...glegroups.com
Subject: Re: [PATCH V3] bcachefs: Add journal v2 entry nr value check

On Wed, Aug 21, 2024 at 10:57:37AM GMT, Lizhi Xu 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@...kaller.appspotmail.com
> Signed-off-by: Lizhi Xu <lizhi.xu@...driver.com>
> ---
>  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.

> +		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);
> -- 
> 2.43.0
>