[PATCH 1/5] Avoid potential block overflow when writing journal metadata tags

When writing block numbers into a journal descriptor block, don't write
the top 32 bits of a tag unless we're using a 64-bit journal.  That
avoids any possibility of overflowing off the end of the descriptor
block in the case where the last 32-bit tag only just fits into the
descriptor block.

Also cleans up the tag handling slightly by introducing new macros for
the size of 32- and 64-bit descriptor tags.

Signed-off-by: Stephen Tweedie <sct@redhat.com>
---
 fs/jbd/commit.c     |   11 ++++++-----
 include/linux/jbd.h |    3 +++
 2 files changed, 9 insertions(+), 5 deletions(-)

diff --git a/fs/jbd/commit.c b/fs/jbd/commit.c
index 680353f..3c2ad09 100644
--- a/fs/jbd/commit.c
+++ b/fs/jbd/commit.c
@@ -160,10 +160,12 @@ static int journal_write_commit_record(j
 	return (ret == -EIO);
 }
 
-static inline void write_split_be64(__be32 *high, __be32 *low, u64 val)
+static inline void write_tag_block(int tag_bytes, journal_block_tag_t *tag,
+				   sector_t block)
 {
-	*low = cpu_to_be32(val & (u32)~0);
-	*high = cpu_to_be32(val >> 32);
+	tag->t_blocknr = cpu_to_be32(block & (u32)~0);
+	if (tag_bytes > JBD_TAG_SIZE32)
+		tag->t_blocknr_high = cpu_to_be32((block >> 31) >> 1);
 }
 
 /*
@@ -560,8 +562,7 @@ write_out_data:
 			tag_flag |= JFS_FLAG_SAME_UUID;
 
 		tag = (journal_block_tag_t *) tagp;
-		write_split_be64(&tag->t_blocknr_high, &tag->t_blocknr,
-				jh2bh(jh)->b_blocknr);
+		write_tag_block(tag_bytes, tag, jh2bh(jh)->b_blocknr);
 		tag->t_flags = cpu_to_be32(tag_flag);
 		tagp += tag_bytes;
 		space_left -= tag_bytes;
diff --git a/include/linux/jbd.h b/include/linux/jbd.h
index 46cbc26..9579bbb 100644
--- a/include/linux/jbd.h
+++ b/include/linux/jbd.h
@@ -159,6 +159,9 @@ typedef struct journal_block_tag_s
 	__be32		t_blocknr_high; /* most-significant high 32bits. */
 } journal_block_tag_t;
 
+#define JBD_TAG_SIZE32 (offsetof(journal_block_tag_t, t_blocknr_high))
+#define JBD_TAG_SIZE64 (sizeof(journal_block_tag_t))
+
 /* 
  * The revoke descriptor: used on disk to describe a series of blocks to
  * be revoked from the log 
-- 
1.4.0


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