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-rw-r--r--target/linux/generic/pending-4.9/142-mtd-bcm47xxpart-improve-handling-TRX-partition-size.patch65
1 files changed, 65 insertions, 0 deletions
diff --git a/target/linux/generic/pending-4.9/142-mtd-bcm47xxpart-improve-handling-TRX-partition-size.patch b/target/linux/generic/pending-4.9/142-mtd-bcm47xxpart-improve-handling-TRX-partition-size.patch
new file mode 100644
index 0000000..60c8ecb
--- /dev/null
+++ b/target/linux/generic/pending-4.9/142-mtd-bcm47xxpart-improve-handling-TRX-partition-size.patch
@@ -0,0 +1,65 @@
+From: =?UTF-8?q?Rafa=C5=82=20Mi=C5=82ecki?= <rafal@milecki.pl>
+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 be a separated 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>
+---
+
+--- 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;
+ }
+