genhd: check for int overflow in disk_expand_part_tbl()

We can get here from blkdev_ioctl() -> blkpg_ioctl() -> add_partition()
with a user passed in partno value. If we pass in 0x7fffffff, the
new target in disk_expand_part_tbl() overflows the 'int' and we
access beyond the end of ptbl->part[] and even write to it when we
do the rcu_assign_pointer() to assign the new partition.

Reported-by: David Ramos <daramos@stanford.edu>
Cc: stable@kernel.org
Signed-off-by: Jens Axboe <axboe@fb.com>

1 files changed, 9 insertions, 2 deletions

diff --git a/block/genhd.c b/block/genhd.c
index bd3060684ab2..0a536dc05f3b 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -1070,9 +1070,16 @@ int disk_expand_part_tbl(struct gendisk *disk, int partno)
         struct disk_part_tbl *old_ptbl = disk->part_tbl;
         struct disk_part_tbl *new_ptbl;
         int len = old_ptbl ? old_ptbl->len : 0;
-        int target = partno + 1;
+        int i, target;
         size_t size;
-        int i;
+
+        /*
+         * check for int overflow, since we can get here from blkpg_ioctl()
+         * with a user passed 'partno'.
+         */
+        target = partno + 1;
+        if (target < 0)
+                return -EINVAL;
 
         /* disk_max_parts() is zero during initialization, ignore if so */
         if (disk_max_parts(disk) && target > disk_max_parts(disk))