CVE-2026-68478 — memstick: ms_block: reject a card that reports too many blocks

Affected: Linux

In the Linux kernel, the following vulnerability has been resolved:

memstick: ms_block: reject a card that reports too many blocks

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.

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CVE-2026-68478 — memstick: ms_block: reject a card that reports too many blocks