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mtd: bcm47xxpart: improve handling TRX partition size

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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>
This commit is contained in:
Rafał Miłecki 2018-04-12 07:24:52 +02:00 committed by Boris Brezillon
parent 5ac67ce36c
commit 237ea0d476
1 changed files with 18 additions and 4 deletions
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22
drivers/mtd/bcm47xxpart.c
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@ -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;
}