dm table: fix invalid memory accesses with too high sector number

If the sector number is too high, dm_table_find_target() should return a
pointer to a zeroed dm_target structure (the caller should test it with
dm_target_is_valid).

However, for some table sizes, the code in dm_table_find_target() that
performs btree lookup will access out of bound memory structures.

Fix this bug by testing the sector number at the beginning of
dm_table_find_target(). Also, add an "inline" keyword to the function
dm_table_get_size() because this is a hot path.

Fixes: 512875b ("dm: table detect io beyond device")
Cc: stable@vger.kernel.org
Reported-by: Zhang Tao <kontais@zoho.com>
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

drivers/md/dm-table.c

@@ -1342,7 +1342,7 @@ void dm_table_event(struct dm_table *t)
 }
 EXPORT_SYMBOL(dm_table_event);
 
-sector_t dm_table_get_size(struct dm_table *t)
+inline sector_t dm_table_get_size(struct dm_table *t)
 {
 	return t->num_targets ? (t->highs[t->num_targets - 1] + 1) : 0;
 }
@@ -1367,6 +1367,9 @@ struct dm_target *dm_table_find_target(struct dm_table *t, sector_t sector)
 	unsigned int l, n = 0, k = 0;
 	sector_t *node;
 
+	if (unlikely(sector >= dm_table_get_size(t)))
+		return &t->targets[t->num_targets];
+
 	for (l = 0; l < t->depth; l++) {
 		n = get_child(n, k);
 		node = get_node(t, l, n);