On Sep 30, 2015, at 11:47 AM, Darrick J. Wong <darrick.wong@xxxxxxxxxx> 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;
> }
Why not use:
WARN_ON_ONCE(journal_has_csum_v2orv3_feature() &&
journal->j_chksum_driver == NULL);
rather than open-coding it? Yes, you would have to move that function
to the header and give it a better name.
As a side note, I've long thought about changing the macros to be shorter:
#define JBD2_HAS_INCOMPAT_FEATURE(j, name) \
((j)->j_format_version >= 2 && \
((j)->j_superblock->s_feature_incompat & \
cpu_to_be32((JBD2_HAS_INCOMPAT_FEATURE_ ## name))))
so they can be used like:
static bool jbd2_journal_has_csum_v2or3_feature(journal_t *journal)
{
return JBD2_HAS_INCOMPAT_FEATURE(journal, CSUM_V2) ||
JBD2_HAS_INCOMPAT_FEATURE(journal, CSUM_V3);
}
This not only makes the code much shorter and more readable, it also
avoids potentially hard-to-spot bugs like the following:
JBD2_HAS_INCOMPAT_FEATURE(j, JBD2_FEATURE_COMPAT_CHECKSUM)
The same would be useful for the equivalent ext4 macros as well.
Cheers, Andreas
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