The old implementation of counting up from a random starting
point had the problem that is allowed an attacker to find out
the write order of the blocks.
This fixes relative symlinks:
$ tar xf linux-4.2.tar.gz
tar: linux-4.2/tools/testing/selftests/powerpc/vphn/vphn.h: Cannot utime: No such file or directory
tar: linux-4.2/tools/testing/selftests/powerpc/vphn/vphn.c: Cannot utime: No such file or directory
tar: linux-4.2/tools/testing/selftests/powerpc/stringloops/memcmp_64.S: Cannot utime: No such file or directory
tar: linux-4.2/tools/testing/selftests/powerpc/primitives/word-at-a-time.h: Cannot utime: No such file or directory
tar: linux-4.2/tools/testing/selftests/powerpc/primitives/asm/asm-compat.h: Cannot utime: No such file or directory
tar: linux-4.2/tools/testing/selftests/powerpc/copyloops/memcpy_power7.S: Cannot utime: No such file or directory
tar: linux-4.2/tools/testing/selftests/powerpc/copyloops/memcpy_64.S: Cannot utime: No such file or directory
tar: linux-4.2/tools/testing/selftests/powerpc/copyloops/copyuser_power7.S: Cannot utime: No such file or directory
tar: linux-4.2/tools/testing/selftests/powerpc/copyloops/copyuser_64.S: Cannot utime: No such file or directory
tar: linux-4.2/arch/powerpc/boot/dts/include/dt-bindings: Cannot utime: No such file or directory
tar: linux-4.2/arch/mips/boot/dts/include/dt-bindings: Cannot utime: No such file or directory
tar: linux-4.2/arch/metag/boot/dts/include/dt-bindings: Cannot utime: No such file or directory
tar: linux-4.2/arch/arm64/boot/dts/include/dt-bindings: Cannot utime: No such file or directory
tar: linux-4.2/arch/arm/boot/dts/include/dt-bindings: Cannot utime: No such file or directory
tar: Exiting with failure status due to previous errors
The too-large reported value broke mmap
(applications saw appended zero bytes)
Also
* Add locking for all fd operations
* Add "--debug" command line switch