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Commit 09a150b3 authored by Jakub Pawlowski's avatar Jakub Pawlowski
Browse files

Remove bytes after first zero length field in legacy advertisements 

This is for compatibility with many existing old devices, that have
non-zero bytes after zero length field. This is currently causing
advertisements to be dropped, rendering those devices invisible.

Bug: 68907583
Test: AdvertiseDataParserTest.RemoveTrailingZerosMalformed
Change-Id: Ib51950f7e0c6a2771f56c6f69108fa10f2517f38
parent 52b06d66

system/stack/btm/btm_ble_gap.cc

+2 −1
Original line number Diff line number Diff line
@@ -2013,7 +2013,8 @@ static void btm_ble_process_adv_pkt_cont( 
  bool is_start =

      ble_evt_type_is_legacy(evt_type) && is_scannable && !is_scan_resp;



  if (is_start) AdvertiseDataParser::RemoveTrailingZeros(tmp);

  if (ble_evt_type_is_legacy(evt_type))

    AdvertiseDataParser::RemoveTrailingZeros(tmp);



  // We might have send scan request to this device before, but didn't get the

  // response. In such case make sure data is put at start, not appended to

system/stack/include/advertise_data_parser.h

+1 −6
Original line number Diff line number Diff line
@@ -57,12 +57,7 @@ class AdvertiseDataParser { 
      // end of the packet. Otherwise i.e. gluing scan response to advertise

      // data will result in data with zero padding in the middle.

      if (len == 0) {

        size_t zeros_start = position;

        for (size_t i = position + 1; i < ad_len; i++) {

          if (ad[i] != 0) return;

        }



        ad.erase(ad.begin() + zeros_start, ad.end());

        ad.erase(ad.begin() + position, ad.end());

        return;

      }

system/stack/test/ad_parser_unittest.cc

+28 −2
Original line number Diff line number Diff line
@@ -137,15 +137,41 @@ TEST(AdvertiseDataParserTest, RemoveTrailingZeros) { 
      0x02, 0x01, 0x02, 0x11, 0x06, 0x66, 0x9a, 0x0c, 0x20, 0x00, 0x08,

      0x37, 0xa8, 0xe5, 0x11, 0x81, 0x8b, 0xd0, 0xf0, 0xf0, 0xf0, 0x00,

      0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00};

  const std::vector<uint8_t> podo_scan_resp{

  std::vector<uint8_t> podo_scan_resp{

      0x03, 0x19, 0x00, 0x80, 0x09, 0x09, 0x50, 0x6f, 0x64, 0x6f, 0x51,

      0x35, 0x56, 0x47, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,

      0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00};



  AdvertiseDataParser::RemoveTrailingZeros(podo_ad_data);

  AdvertiseDataParser::RemoveTrailingZeros(podo_scan_resp);



  std::vector<uint8_t> glued(podo_ad_data);

  glued.insert(glued.end(), podo_ad_data.begin(), podo_ad_data.end());

  glued.insert(glued.end(), podo_scan_resp.begin(), podo_scan_resp.end());



  EXPECT_TRUE(AdvertiseDataParser::IsValid(glued));

}



// This test makes sure that RemoveTrailingZeros is removing all bytes after

// first zero length field. It does run the RemoveTrailingZeros for data with

// non-zero bytes after zero length field, then glue scan response at end of it,

// and checks that the resulting data is good. Note: specification requires all

// bytes after zero length field to be zero padding, but many legacy devices got

// this wrong, causing us to have this workaround.

TEST(AdvertiseDataParserTest, RemoveTrailingZerosMalformed) {

  std::vector<uint8_t> ad_data{0x02, 0x01, 0x02, 0x11, 0x06, 0x66, 0x9a, 0x0c,

                               0x20, 0x00, 0x08, 0x37, 0xa8, 0xe5, 0x11, 0x81,

                               0x8b, 0xd0, 0xf0, 0xf0, 0xf0, 0x00, 0xFF, 0xFF,

                               0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF};

  std::vector<uint8_t> scan_resp{0x03, 0x19, 0x00, 0x80, 0x09, 0x09, 0x50, 0x6f,

                                 0x64, 0x6f, 0x51, 0x35, 0x56, 0x47, 0x00, 0xFF,

                                 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,

                                 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF};



  AdvertiseDataParser::RemoveTrailingZeros(ad_data);

  AdvertiseDataParser::RemoveTrailingZeros(scan_resp);



  std::vector<uint8_t> glued(ad_data);

  glued.insert(glued.end(), scan_resp.begin(), scan_resp.end());



  EXPECT_TRUE(AdvertiseDataParser::IsValid(glued));

}
 
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