Re: [PATCH] jbd2: gate checksum calculations on crc driver presence, not sb flags

[Nikolay Borisov]

On 09/30/2015 08:47 PM, Darrick J. Wong wrote:
> Change the journal's checksum functions to gate on whether or not the
> crc32c driver is loaded, and gate the loading on the superblock bits.
> This prevents a journal crash if someone loads a journal in no-csum
> mode and then randomizes the superblock, thus flipping on the feature
> bits.
> 
> Reported-by: Nikolay Borisov <kernel@xxxxxxxx>
> Signed-off-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
> ---
>  fs/jbd2/journal.c    |   12 +++++++++---
>  include/linux/jbd2.h |   10 ++++++----
>  2 files changed, 15 insertions(+), 7 deletions(-)
> 
> diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
> index 8270fe9..16e3a46 100644
> --- a/fs/jbd2/journal.c
> +++ b/fs/jbd2/journal.c
> @@ -122,9 +122,15 @@ EXPORT_SYMBOL(__jbd2_debug);
>  #endif
>  
>  /* Checksumming functions */
> +static bool journal_has_csum_v2or3_feature(journal_t *j)
> +{
> +	return JBD2_HAS_INCOMPAT_FEATURE(j, JBD2_FEATURE_INCOMPAT_CSUM_V2) ||
> +	       JBD2_HAS_INCOMPAT_FEATURE(j, JBD2_FEATURE_INCOMPAT_CSUM_V3);
> +}
> +
>  static int jbd2_verify_csum_type(journal_t *j, journal_superblock_t *sb)
>  {
> -	if (!jbd2_journal_has_csum_v2or3(j))
> +	if (!journal_has_csum_v2or3_feature(j))
>  		return 1;
>  
>  	return sb->s_checksum_type == JBD2_CRC32C_CHKSUM;
> @@ -1531,7 +1537,7 @@ static int journal_get_superblock(journal_t *journal)
>  		goto out;
>  	}
>  
> -	if (jbd2_journal_has_csum_v2or3(journal) &&
> +	if (journal_has_csum_v2or3_feature(journal) &&
>  	    JBD2_HAS_COMPAT_FEATURE(journal, JBD2_FEATURE_COMPAT_CHECKSUM)) {
>  		/* Can't have checksum v1 and v2 on at the same time! */
>  		printk(KERN_ERR "JBD2: Can't enable checksumming v1 and v2/3 "
> @@ -1545,7 +1551,7 @@ static int journal_get_superblock(journal_t *journal)
>  	}
>  
>  	/* Load the checksum driver */
> -	if (jbd2_journal_has_csum_v2or3(journal)) {
> +	if (journal_has_csum_v2or3_feature(journal)) {
>  		journal->j_chksum_driver = crypto_alloc_shash("crc32c", 0, 0);
>  		if (IS_ERR(journal->j_chksum_driver)) {
>  			printk(KERN_ERR "JBD2: Cannot load crc32c driver.\n");
> diff --git a/include/linux/jbd2.h b/include/linux/jbd2.h
> index df07e78..c74c786 100644
> --- a/include/linux/jbd2.h
> +++ b/include/linux/jbd2.h
> @@ -1340,11 +1340,13 @@ extern size_t journal_tag_bytes(journal_t *journal);
>  
>  static inline int jbd2_journal_has_csum_v2or3(journal_t *journal)
>  {
> -	if (JBD2_HAS_INCOMPAT_FEATURE(journal, JBD2_FEATURE_INCOMPAT_CSUM_V2) ||
> -	    JBD2_HAS_INCOMPAT_FEATURE(journal, JBD2_FEATURE_INCOMPAT_CSUM_V3))
> -		return 1;
> +	WARN_ON_ONCE((JBD2_HAS_INCOMPAT_FEATURE(journal,
> +				JBD2_FEATURE_INCOMPAT_CSUM_V2) ||
> +		 JBD2_HAS_INCOMPAT_FEATURE(journal,
> +				JBD2_FEATURE_INCOMPAT_CSUM_V3)) &&
> +		     journal->j_chksum_driver == NULL);
>  
> -	return 0;
> +	return journal->j_chksum_driver != NULL;
>  }
>  
>  /*

Tested-By: Nikolay Borisov <kernel@xxxxxxxx>
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