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xfs: ensure correct log item buffer alignment

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On 32 bit platforms, the log item vector headers are not 64 bit
aligned or sized. hence if we don't take care to align them
correctly or pad the buffer appropriately for 8 byte alignment, we
can end up with alignment issues when accessing the user buffer
directly as a structure.

To solve this, simply pad the buffer headers to 64 bit offset so
that the data section is always 8 byte aligned.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reported-by: Michael L. Semon <mlsemon35@gmail.com>
Tested-by: Michael L. Semon <mlsemon35@gmail.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Dave Chinner <david@fromorbit.com>
This commit is contained in:
Dave Chinner 2014-02-10 10:37:18 +11:00 committed by Dave Chinner
parent fe60a8a091
commit 3895e51f6d
1 changed files with 15 additions and 4 deletions
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19
fs/xfs/xfs_log_cil.c
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@ -205,16 +205,25 @@ xlog_cil_insert_format_items(
/*
* We 64-bit align the length of each iovec so that the start
* of the next one is naturally aligned. We'll need to
* account for that slack space here.
* account for that slack space here. Then round nbytes up
* to 64-bit alignment so that the initial buffer alignment is
* easy to calculate and verify.
*/
nbytes += niovecs * sizeof(uint64_t);
nbytes = round_up(nbytes, sizeof(uint64_t));
/* grab the old item if it exists for reservation accounting */
old_lv = lip->li_lv;
/* calc buffer size */
buf_size = sizeof(struct xfs_log_vec) + nbytes +
niovecs * sizeof(struct xfs_log_iovec);
/*
* The data buffer needs to start 64-bit aligned, so round up
* that space to ensure we can align it appropriately and not
* overrun the buffer.
*/
buf_size = nbytes +
round_up((sizeof(struct xfs_log_vec) +
niovecs * sizeof(struct xfs_log_iovec)),
sizeof(uint64_t));
/* compare to existing item size */
if (lip->li_lv && buf_size <= lip->li_lv->lv_size) {
@ -251,6 +260,8 @@ xlog_cil_insert_format_items(
/* The allocated data region lies beyond the iovec region */
lv->lv_buf_len = 0;
lv->lv_buf = (char *)lv + buf_size - nbytes;
ASSERT(IS_ALIGNED((unsigned long)lv->lv_buf, sizeof(uint64_t)));
lip->li_ops->iop_format(lip, lv);
insert:
ASSERT(lv->lv_buf_len <= nbytes);