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>

diff --git a/block/genhd.c b/block/genhd.c
index bd3060684ab2f0cb3f0e926f6ac62071442709a7..0a536dc05f3b559d6d04c1e819d65290f96f7c35 100644 (file)
--- 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))