mtd: bcm47xxpart: improve handling TRX partition size (237ea0d4) · Commits · 戴 / test

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 <rafal@milecki.pl> Signed-off-by:

Boris Brezillon <boris.brezillon@bootlin.com>

drivers/mtd/bcm47xxpart.c

+18 −4

Original line number	Diff line number	Diff line
		@@ -186,6 +186,8 @@ static int bcm47xxpart_parse(struct mtd_info *master,
		/* 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_info *master,
		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;
		}

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