This program aims to rebuild ADB backup files that were corrupted by --shared on Android versions 4.0.3 / 4.0.4.
The corrupt ADB backup files are still fully usable and contain no data loss. Instead, the problem is that an uncompressed chunk of data is written to the file directly -- bypassing any encryption and all compression. Additionally, this happens before the encryption/compression are able to finish writing out the compressed data which causes decryption and inflation routines to fail.
Standard TAR file header blocks contain the text "ustar", so this text is used to identify the beginning of uncompressed data within the input file.
Android's native C++ code chunks the uncompressed TAR data into blocks of up to 32768 bytes, prepends the byte-size of each block, and sends it back to Java code to be compressed and included into the backup file. Prior to Android 4.1, shared storage TAR data (including chunk sizes) was dumped directly to the output file. To pull it out, each chunk is read and written to a shared data TAR.
A chunk size of 0 is used to indicate EOD (End of Data), so this can also be used to determine the location that compressed data resumes.
Because the corrupted data is not decrypted or parsed in any way, no password input or external libraries are required.
Only a working C compiler with standard libraries should be required.
This has only been tested with GCC in Linux, built and working with the following commands:
gcc rebuild-adb-backup.c
./a.out <backup.ab> [fixed_backup.ab] [shared_data.tar]
- backup.ab: The backup file that was incorrectly built by Android
- fixed_backup.ab: The target filename to rebuild the backup.ab file into. The default is fixed_backup.ab.
- shared_data.tar: The target filename to extract the uncompressed shared storage TAR. The default is shared_data.tar.
Warning: This will overwrite any output file without confirmation. Do NOT specify the same input and output file.
- Contributors to XDA's Perl scripts to encrypt/decrypt adb backup files
thread:
- puterboy for tarfix.pl as an initial pointer into how the TAR file was chunked, even though his description isn't fully accurate.
- binaryhero for better description of uncompressed data being dumped into the middle of the output data file
- GrepCode for hosting the Java parts of Android's API source
The MIT License (MIT)
Copyright (c) 2013 Robert Grimm
Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
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