The abuild-tar binary can read past the end of an invalid tar header if
the contained link name does not end with a terminating NUL character.
In this case it reads past the end of hdr.linkname and maybe even past
the end of the header if no further NUL bytes are contained.
The strnlen function is used in apk-tools for such cases as well, so I
recommend to use it here too.
How to reproduce (compile abuild-tar with -fsanitize=address):
cat > poc.tar.b64 << EOF
b3dvAAAAAAAAAAADAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAADAwMDAwMDAAMDAwMDAw
MAAwMDAwMDAwADAwMDAwMDAwMDAwADAwMDAwMDAwMDAwADAwMDAwMAAAMm93b29vb29vb29vb29v
b29vb29vb29vb29vb29vb29vb29vb29vb29vb29vb29vb29vb29vb29vb29vb29vb29vb29vb29v
b29vb29vb29vb29vb29vb29vb29vb29vb29vb29vb29vb29vb29vb29vb29vb29vb29vb29vb29v
b29vb29vb29vb29vb29vb29vb29vb29vb29vb29vb29vb29vb29vb29vb29vb29vb29vb29vb29v
b29vb29vb29vb29vb29vb29vb29vb29vb29vb29vb29vb29vb29vb29vb29vb29vb29vb29vb29v
b29vb29vb29vb29vb29vb29vb29vb29vb29vb29vb29vb29vb29vb29vb29vb29vb29vb29vb29v
b29vb29vb29vb29vb29vb29vb29vb29vb29vb29vb29vb29vb29vb29vb29vb29vb29vb29vb28=
EOF
base64 -d < poc.tar.b64 | abuild-tar --hash
Arithmetic operations with void pointers are an extension by some
compilers and not part of the C standard, which does not specify the
size of void.
CFLAGS with -pedantic reveals this during compile time. I have adjusted
the usage of ?: so CFLAGS can contain -pedantic now.
- ability to embed an checksum inside the tar header for regular
files (to avoid checksumming at apk installation time)
- way to remove the end-of-archive marker to create concenatable
.tar.gz:s for signed apks