[PATCH] block: Don't allow illegal discard requests

[Jan Kara <jack@suse.com>]

Currently blkdev_issue_discard() doesn't check that submitted discard
request matches granularity required by the underlying device.
Submitting such requests to the device can have unexpected consequences
(e.g. brd driver just discards more / less data depending on how exactly
the request is aligned). So test that submitted discard request has the
granularity required by the driver.

Signed-off-by: Jan Kara <jack@suse.com>
---
 block/blk-lib.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/block/blk-lib.c b/block/blk-lib.c
index bd40292e5009..7170d02e9e9a 100644
--- a/block/blk-lib.c
+++ b/block/blk-lib.c
@@ -61,6 +61,13 @@ int blkdev_issue_discard(struct block_device *bdev, sector_t sector,
 	if (!blk_queue_discard(q))
 		return -EOPNOTSUPP;
 
+	if (q->limits.discard_granularity) {
+		unsigned int gran_sect = q->limits.discard_granularity >> 9;
+
+		if (sector % gran_sect || nr_sects % gran_sect)
+			return -EINVAL;
+	}
+
 	if (flags & BLKDEV_DISCARD_SECURE) {
 		if (!blk_queue_secdiscard(q))
 			return -EOPNOTSUPP;
-- 
2.1.4