[PATCH 3.16.y-ckt 064/126] mac: validate mac_partition is within sector

[Luis Henriques]

3.16.7-ckt22 -stable review patch.  If anyone has any objections, please let me 
know.

------------------

From: Kees Cook <keesc...@chromium.org>

commit 02e2a5bfebe99edcf9d694575a75032d53fe1b73 upstream.

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 <keesc...@chromium.org>
Signed-off-by: Jens Axboe <ax...@fb.com>
Signed-off-by: Luis Henriques <luis.henriq...@canonical.com>
---
 block/partitions/mac.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/block/partitions/mac.c b/block/partitions/mac.c
index 76d8ba6379a9..bd5b91465230 100644
--- 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 */
--
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