[PATCH] memstick: ms_block: reject a card that reports too many blocks

[Maoyi Xie <maoyixie.tju@gmail.com>]

msb_ftl_initialize() computes the zone count from the card block count
with no bound:

	msb->zone_count = msb->block_count / MS_BLOCKS_IN_ZONE;
	...
	for (i = 0; i < msb->zone_count; i++)
		msb->free_block_count[i] = MS_BLOCKS_IN_ZONE;

msb->block_count is a card value. msb_read_boot_blocks() reads
number_of_blocks from the card boot page and byte swaps it.
free_block_count is a fixed int[MS_MAX_ZONES]. MS_MAX_ZONES is 16, so the
valid indices are 0 to 15. The init loop above indexes it by zone_count.
msb_mark_block_used() and msb_mark_block_unused() index it by
pba / MS_BLOCKS_IN_ZONE, for pba up to block_count - 1. A card may report
up to 65535 blocks. A block_count above 8192 (MS_MAX_ZONES *
MS_BLOCKS_IN_ZONE) lets the pba index reach 16. That writes past
free_block_count[] and corrupts struct msb_data. A larger count runs the
init loop past the end too.

A real Memory Stick has at most 16 zones. So it has at most 8192 blocks.
msb_ftl_initialize() now rejects a card that reports more than
MS_MAX_ZONES * MS_BLOCKS_IN_ZONE blocks.

Fixes: 0ab30494bc4f ("memstick: add support for legacy memorysticks")
Cc: stable@vger.kernel.org
Signed-off-by: Maoyi Xie <maoyixie.tju@gmail.com>
---
I do not have the hardware. I showed the overflow with a small harness.
The harness replays the store loop into free_block_count[].

 drivers/memstick/core/ms_block.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/memstick/core/ms_block.c b/drivers/memstick/core/ms_block.c
index a01fe31355..ce33907bfc 100644
--- a/drivers/memstick/core/ms_block.c
+++ b/drivers/memstick/core/ms_block.c
@@ -1338,6 +1338,10 @@ static int msb_ftl_initialize(struct msb_data *msb)
 		return 0;
 
 	msb->zone_count = msb->block_count / MS_BLOCKS_IN_ZONE;
+	if (msb->block_count > MS_MAX_ZONES * MS_BLOCKS_IN_ZONE) {
+		pr_err("Too many blocks: %d\n", msb->block_count);
+		return -EINVAL;
+	}
 	msb->logical_block_count = msb->zone_count * 496 - 2;
 
 	msb->used_blocks_bitmap = bitmap_zalloc(msb->block_count, GFP_KERNEL);
-- 
2.34.1