From: Dave Chinner <dchinner@xxxxxxxxxx>
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@xxxxxxxxxx>
---
fs/xfs/xfs_log_cil.c | 19 +++++++++++++++----
1 file changed, 15 insertions(+), 4 deletions(-)
diff --git a/fs/xfs/xfs_log_cil.c b/fs/xfs/xfs_log_cil.c
index cdebd83..4ef6fdb 100644
--- a/fs/xfs/xfs_log_cil.c
+++ b/fs/xfs/xfs_log_cil.c
@@ -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);
--
1.8.4.rc3
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