This adds a couple of BUILD_BUG_ON()s and moves some arithmetic after
the validation code that checks the arithmetic’s preconditions. The
previous code was correct but could potentially trip sanitizers that
check for unsigned integer wraparound.
Signed-off-by: Demi Marie Obenour <demi@xxxxxxxxxxxxxxxxxxxxxx>
---
drivers/block/xen-blkback/blkback.c | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)
diff --git a/drivers/block/xen-blkback/blkback.c b/drivers/block/xen-blkback/blkback.c
index c362f4ad80ab07bfb58caff0ed7da37dc1484fc5..ac760a08d559085ab875784f1c58cdf2ead95a43 100644
--- a/drivers/block/xen-blkback/blkback.c
+++ b/drivers/block/xen-blkback/blkback.c
@@ -1342,6 +1342,8 @@ static int dispatch_rw_block_io(struct xen_blkif_ring *ring,
nseg = req->operation == BLKIF_OP_INDIRECT ?
req->u.indirect.nr_segments : req->u.rw.nr_segments;
+ BUILD_BUG_ON(offsetof(struct blkif_request, u.rw.id) != 8);
+ BUILD_BUG_ON(offsetof(struct blkif_request, u.indirect.id) != 8);
if (unlikely(nseg == 0 && operation_flags != REQ_PREFLUSH) ||
unlikely((req->operation != BLKIF_OP_INDIRECT) &&
(nseg > BLKIF_MAX_SEGMENTS_PER_REQUEST)) ||
@@ -1365,13 +1367,13 @@ static int dispatch_rw_block_io(struct xen_blkif_ring *ring,
preq.sector_number = req->u.rw.sector_number;
for (i = 0; i < nseg; i++) {
pages[i]->gref = req->u.rw.seg[i].gref;
- seg[i].nsec = req->u.rw.seg[i].last_sect -
- req->u.rw.seg[i].first_sect + 1;
- seg[i].offset = (req->u.rw.seg[i].first_sect << 9);
if ((req->u.rw.seg[i].last_sect >= (XEN_PAGE_SIZE >> 9)) ||
(req->u.rw.seg[i].last_sect <
req->u.rw.seg[i].first_sect))
goto fail_response;
+ seg[i].nsec = req->u.rw.seg[i].last_sect -
+ req->u.rw.seg[i].first_sect + 1;
+ seg[i].offset = (req->u.rw.seg[i].first_sect << 9);
preq.nr_sects += seg[i].nsec;
}
} else {
--
Sincerely,
Demi Marie Obenour (she/her/hers)
Invisible Things Lab
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