dm: fix improper splitting for abnormal bios

"Abnormal" bios include discards, write zeroes and secure erase. By no
longer passing the calculated 'len' pointer, commit 7dd06a2 ("dm:
allow dm_accept_partial_bio() for dm_io without duplicate bios") took a
senseless approach to disallowing dm_accept_partial_bio() from working
for duplicate bios processed using __send_duplicate_bios().

It inadvertently and incorrectly stopped the use of 'len' when
initializing a target's io (in alloc_tio). As such the resulting tio
could address more area of a device than it should.

For example, when discarding an entire DM striped device with the
following DM table:
 vg-lvol0: 0 159744 striped 2 128 7:0 2048 7:1 2048
 vg-lvol0: 159744 45056 striped 2 128 7:2 2048 7:3 2048

Before this fix:

 device-mapper: striped: target_stripe=0, bdev=7:0, start=2048 len=102400
 blkdiscard: attempt to access beyond end of device
 loop0: rw=2051, sector=2048, nr_sectors = 102400 limit=81920

 device-mapper: striped: target_stripe=1, bdev=7:1, start=2048 len=102400
 blkdiscard: attempt to access beyond end of device
 loop1: rw=2051, sector=2048, nr_sectors = 102400 limit=81920

After this fix;

 device-mapper: striped: target_stripe=0, bdev=7:0, start=2048 len=79872
 device-mapper: striped: target_stripe=1, bdev=7:1, start=2048 len=79872

Fixes: 7dd06a2 ("dm: allow dm_accept_partial_bio() for dm_io without duplicate bios")
Cc: [email protected]
Reported-by: Orange Kao <[email protected]>
Signed-off-by: Mike Snitzer <[email protected]>

drivers/md/dm.c

@@ -1467,7 +1467,8 @@ static void setup_split_accounting(struct clone_info *ci, unsigned int len)
 }
 
 static void alloc_multiple_bios(struct bio_list *blist, struct clone_info *ci,
-				struct dm_target *ti, unsigned int num_bios)
+				struct dm_target *ti, unsigned int num_bios,
+				unsigned *len)
 {
 	struct bio *bio;
 	int try;
@@ -1478,7 +1479,7 @@ static void alloc_multiple_bios(struct bio_list *blist, struct clone_info *ci,
 		if (try)
 			mutex_lock(&ci->io->md->table_devices_lock);
 		for (bio_nr = 0; bio_nr < num_bios; bio_nr++) {
-			bio = alloc_tio(ci, ti, bio_nr, NULL,
+			bio = alloc_tio(ci, ti, bio_nr, len,
 					try ? GFP_NOIO : GFP_NOWAIT);
 			if (!bio)
 				break;
@@ -1514,7 +1515,7 @@ static int __send_duplicate_bios(struct clone_info *ci, struct dm_target *ti,
 		break;
 	default:
 		/* dm_accept_partial_bio() is not supported with shared tio->len_ptr */
-		alloc_multiple_bios(&blist, ci, ti, num_bios);
+		alloc_multiple_bios(&blist, ci, ti, num_bios, len);
 		while ((clone = bio_list_pop(&blist))) {
 			dm_tio_set_flag(clone_to_tio(clone), DM_TIO_IS_DUPLICATE_BIO);
 			__map_bio(clone);