From 237ea0d4762cc14d0fc80e80d61f0f08e1050c7f Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Rafa=C5=82=20Mi=C5=82ecki?= Date: Thu, 12 Apr 2018 07:24:52 +0200 Subject: [PATCH] mtd: bcm47xxpart: improve handling TRX partition size MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit When bcm47xxpart finds a TRX partition (container) it's supposed to jump to the end of it and keep looking for more partitions. TRX and its subpartitions are handled by a separate parser. The problem with old code was relying on the length specified in a TRX header. That isn't reliable as TRX is commonly modified to have checksum cover only non-changing subpartitions. Otherwise modifying e.g. a rootfs would result in CRC32 mismatch and bootloader refusing to boot a firmware. Fix it by trying better to figure out a real TRX size. We can securely assume that TRX has to cover all subpartitions and the last one is at least of a block size in size. Then compare it with a length field. This makes code more optimal & reliable thanks to skipping data that shouldn't be parsed. Signed-off-by: Rafał Miłecki Signed-off-by: Boris Brezillon --- drivers/mtd/bcm47xxpart.c | 22 ++++++++++++++++++---- 1 file changed, 18 insertions(+), 4 deletions(-) --- a/drivers/mtd/bcm47xxpart.c +++ b/drivers/mtd/bcm47xxpart.c @@ -186,6 +186,8 @@ static int bcm47xxpart_parse(struct mtd_ /* TRX */ if (buf[0x000 / 4] == TRX_MAGIC) { struct trx_header *trx; + uint32_t last_subpart; + uint32_t trx_size; if (trx_num >= ARRAY_SIZE(trx_parts)) pr_warn("No enough space to store another TRX found at 0x%X\n", @@ -195,11 +197,23 @@ static int bcm47xxpart_parse(struct mtd_ bcm47xxpart_add_part(&parts[curr_part++], "firmware", offset, 0); - /* Jump to the end of TRX */ + /* + * Try to find TRX size. The "length" field isn't fully + * reliable as it could be decreased to make CRC32 cover + * only part of TRX data. It's commonly used as checksum + * can't cover e.g. ever-changing rootfs partition. + * Use offsets as helpers for assuming min TRX size. + */ trx = (struct trx_header *)buf; - offset = roundup(offset + trx->length, blocksize); - /* Next loop iteration will increase the offset */ - offset -= blocksize; + last_subpart = max3(trx->offset[0], trx->offset[1], + trx->offset[2]); + trx_size = max(trx->length, last_subpart + blocksize); + + /* + * Skip the TRX data. Decrease offset by block size as + * the next loop iteration will increase it. + */ + offset += roundup(trx_size, blocksize) - blocksize; continue; }