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Subject[RFC][Update][Patch 8/16]Avoid potential block overflow when writing journal metadata tags
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Date
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>
Acked-by: Badari Pulavarty <pbadari@us.ibm.com>


---
linux-2.6.17-ming/fs/jbd/commit.c | 11 ++++++-----
linux-2.6.17-ming/include/linux/jbd.h | 3 +++
2 files changed, 9 insertions(+), 5 deletions(-)
diff -puN fs/jbd/commit.c~jbd-avoid-blk-overflow-write-journal-metadata-tag fs/jbd/commit.c
--- linux-2.6.17/fs/jbd/commit.c~jbd-avoid-blk-overflow-write-journal-metadata-tag 2006-06-28 16:46:58.783710948 -0700
+++ linux-2.6.17-ming/fs/jbd/commit.c 2006-06-28 16:46:58.791710030 -0700
@@ -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 -puN include/linux/jbd.h~jbd-avoid-blk-overflow-write-journal-metadata-tag include/linux/jbd.h
--- linux-2.6.17/include/linux/jbd.h~jbd-avoid-blk-overflow-write-journal-metadata-tag 2006-06-28 16:46:58.787710489 -0700
+++ linux-2.6.17-ming/include/linux/jbd.h 2006-06-28 16:46:58.793709801 -0700
@@ -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
_


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