linux-ext4 - Re: [PATCH v2] jbd2: fix r_count overflows leading to buffer overflow in journal recovery

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Date:	Thu, 14 May 2015 22:48:26 +0200
From:	Jan Kara <jack@...e.cz>
To:	"Darrick J. Wong" <darrick.wong@...cle.com>
Cc:	tytso@....edu, Jan Kara <jack@...e.cz>, linux-ext4@...r.kernel.org
Subject: Re: [PATCH v2] jbd2: fix r_count overflows leading to buffer
 overflow in journal recovery

On Thu 14-05-15 12:34:24, Darrick J. Wong wrote:
> The journal revoke block recovery code does not check r_count for
> sanity, which means that an evil value of r_count could result in
> the kernel reading off the end of the revoke table and into whatever
> garbage lies beyond.  This could crash the kernel, so fix that.
> 
> However, in testing this fix, I discovered that the code to write
> out the revoke tables also was not correctly checking to see if the
> block was full -- the current offset check is fine so long as the
> revoke table space size is a multiple of the record size, but this
> is not true when either journal_csum_v[23] are set.
> 
> v2: The comparison on the revoke block writer code should allow the
> revoke block to become totally full.
> 
> Signed-off-by: Darrick J. Wong <darrick.wong@...cle.com>
  Looks good. You can add:
Reviewed-by: Jan Kara <jack@...e.cz>

								Honza

> ---
>  fs/jbd2/recovery.c |   10 +++++++++-
>  fs/jbd2/revoke.c   |   18 ++++++++++--------
>  2 files changed, 19 insertions(+), 9 deletions(-)
> 
> diff --git a/fs/jbd2/recovery.c b/fs/jbd2/recovery.c
> index b5128c6..a9079d0 100644
> --- a/fs/jbd2/recovery.c
> +++ b/fs/jbd2/recovery.c
> @@ -842,15 +842,23 @@ static int scan_revoke_records(journal_t *journal, struct buffer_head *bh,
>  {
>  	jbd2_journal_revoke_header_t *header;
>  	int offset, max;
> +	int csum_size = 0;
> +	__u32 rcount;
>  	int record_len = 4;
>  
>  	header = (jbd2_journal_revoke_header_t *) bh->b_data;
>  	offset = sizeof(jbd2_journal_revoke_header_t);
> -	max = be32_to_cpu(header->r_count);
> +	rcount = be32_to_cpu(header->r_count);
>  
>  	if (!jbd2_revoke_block_csum_verify(journal, header))
>  		return -EINVAL;
>  
> +	if (jbd2_journal_has_csum_v2or3(journal))
> +		csum_size = sizeof(struct jbd2_journal_revoke_tail);
> +	if (rcount > journal->j_blocksize - csum_size)
> +		return -EINVAL;
> +	max = rcount;
> +
>  	if (JBD2_HAS_INCOMPAT_FEATURE(journal, JBD2_FEATURE_INCOMPAT_64BIT))
>  		record_len = 8;
>  
> diff --git a/fs/jbd2/revoke.c b/fs/jbd2/revoke.c
> index c6cbaef..14214da 100644
> --- a/fs/jbd2/revoke.c
> +++ b/fs/jbd2/revoke.c
> @@ -577,7 +577,7 @@ static void write_one_revoke_record(journal_t *journal,
>  {
>  	int csum_size = 0;
>  	struct buffer_head *descriptor;
> -	int offset;
> +	int sz, offset;
>  	journal_header_t *header;
>  
>  	/* If we are already aborting, this all becomes a noop.  We
> @@ -594,9 +594,14 @@ static void write_one_revoke_record(journal_t *journal,
>  	if (jbd2_journal_has_csum_v2or3(journal))
>  		csum_size = sizeof(struct jbd2_journal_revoke_tail);
>  
> +	if (JBD2_HAS_INCOMPAT_FEATURE(journal, JBD2_FEATURE_INCOMPAT_64BIT))
> +		sz = 8;
> +	else
> +		sz = 4;
> +
>  	/* Make sure we have a descriptor with space left for the record */
>  	if (descriptor) {
> -		if (offset >= journal->j_blocksize - csum_size) {
> +		if (offset + sz > journal->j_blocksize - csum_size) {
>  			flush_descriptor(journal, descriptor, offset, write_op);
>  			descriptor = NULL;
>  		}
> @@ -619,16 +624,13 @@ static void write_one_revoke_record(journal_t *journal,
>  		*descriptorp = descriptor;
>  	}
>  
> -	if (JBD2_HAS_INCOMPAT_FEATURE(journal, JBD2_FEATURE_INCOMPAT_64BIT)) {
> +	if (JBD2_HAS_INCOMPAT_FEATURE(journal, JBD2_FEATURE_INCOMPAT_64BIT))
>  		* ((__be64 *)(&descriptor->b_data[offset])) =
>  			cpu_to_be64(record->blocknr);
> -		offset += 8;
> -
> -	} else {
> +	else
>  		* ((__be32 *)(&descriptor->b_data[offset])) =
>  			cpu_to_be32(record->blocknr);
> -		offset += 4;
> -	}
> +	offset += sz;
>  
>  	*offsetp = offset;
>  }
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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