mac: validate mac_partition is within sector

If md->signature == MAC_DRIVER_MAGIC and md->block_size == 1023, a single
512 byte sector would be read (secsize / 512). However the partition
structure would be located past the end of the buffer (secsize % 512).

Signed-off-by: Kees Cook <keescook@chromium.org>
Cc: stable@vger.kernel.org
Signed-off-by: Jens Axboe <axboe@fb.com>

diff --git a/block/partitions/mac.c b/block/partitions/mac.c
index c2c48ec64b2709c5f252e164bc3397df0c439210..621317ac4d59f5fd75e433718a194bad7b1c2a56 100644 (file)
--- a/block/partitions/mac.c
+++ b/block/partitions/mac.c
@@ -32,7 +32,7 @@ int mac_partition(struct parsed_partitions *state)
        Sector sect;
        unsigned char *data;
        int slot, blocks_in_map;
-       unsigned secsize;
+       unsigned secsize, datasize, partoffset;
 #ifdef CONFIG_PPC_PMAC
        int found_root = 0;
        int found_root_goodness = 0;
@@ -50,10 +50,14 @@ int mac_partition(struct parsed_partitions *state)
        }
        secsize = be16_to_cpu(md->block_size);
        put_dev_sector(sect);
-       data = read_part_sector(state, secsize/512, &sect);
+       datasize = round_down(secsize, 512);
+       data = read_part_sector(state, datasize / 512, &sect);
        if (!data)
                return -1;
-       part = (struct mac_partition *) (data + secsize%512);
+       partoffset = secsize % 512;
+       if (partoffset + sizeof(*part) > datasize)
+               return -1;
+       part = (struct mac_partition *) (data + partoffset);
        if (be16_to_cpu(part->signature) != MAC_PARTITION_MAGIC) {
                put_dev_sector(sect);
                return 0;               /* not a MacOS disk */