target/linux/generic/patches-4.4/141-mtd-bcm47xxpart-improve-handling-TRX-partition-size.patch

   1 From: =?UTF-8?q?Rafa=C5=82=20Mi=C5=82ecki?= <rafal@milecki.pl>
   2 Subject: [PATCH] mtd: bcm47xxpart: improve handling TRX partition size
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   6
   7 When bcm47xxpart finds a TRX partition (container) it's supposed to jump
   8 to the end of it and keep looking for more partitions. TRX and its
   9 subpartitions are handled be a separated parser.
  10
  11 The problem with old code was relying on the length specified in a TRX
  12 header. That isn't reliable as TRX is commonly modified to have checksum
  13 cover only non-changing subpartitions. Otherwise modifying e.g. a rootfs
  14 would result in CRC32 mismatch and bootloader refusing to boot a
  15 firmware.
  16
  17 Fix it by trying better to figure out a real TRX size. We can securely
  18 assume that TRX has to cover all subpartitions and the last one is at
  19 least of a block size in size. Then compare it with a length field.
  20
  21 This makes code more optimal & reliable thanks to skipping data that
  22 shouldn't be parsed.
  23
  24 Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
  25 ---
  26
  27 --- a/drivers/mtd/bcm47xxpart.c
  28 +++ b/drivers/mtd/bcm47xxpart.c
  29 @@ -268,6 +268,8 @@ static int bcm47xxpart_parse(struct mtd_
  30                 /* TRX */
  31                 if (buf[0x000 / 4] == TRX_MAGIC) {
  32                         struct trx_header *trx;
  33 +                       uint32_t last_subpart;
  34 +                       uint32_t trx_size;
  35
  36                         if (trx_num >= ARRAY_SIZE(trx_parts))
  37                                 pr_warn("No enough space to store another TRX found at 0x%X\n",
  38 @@ -277,11 +279,23 @@ static int bcm47xxpart_parse(struct mtd_
  39                         bcm47xxpart_add_part(&parts[curr_part++], "firmware",
  40                                              offset, 0);
  41
  42 -                       /* Jump to the end of TRX */
  43 +                       /*
  44 +                        * Try to find TRX size. The "length" field isn't fully
  45 +                        * reliable as it could be decreased to make CRC32 cover
  46 +                        * only part of TRX data. It's commonly used as checksum
  47 +                        * can't cover e.g. ever-changing rootfs partition.
  48 +                        * Use offsets as helpers for assuming min TRX size.
  49 +                        */
  50                         trx = (struct trx_header *)buf;
  51 -                       offset = roundup(offset + trx->length, blocksize);
  52 -                       /* Next loop iteration will increase the offset */
  53 -                       offset -= blocksize;
  54 +                       last_subpart = max3(trx->offset[0], trx->offset[1],
  55 +                                           trx->offset[2]);
  56 +                       trx_size = max(trx->length, last_subpart + blocksize);
  57 +
  58 +                       /*
  59 +                        * Skip the TRX data. Decrease offset by block size as
  60 +                        * the next loop iteration will increase it.
  61 +                        */
  62 +                       offset += roundup(trx_size, blocksize) - blocksize;
  63                         continue;
  64                 }
  65