buildgcc: Implement simple tarball hash verification
This patch implements a relatively simple hash-based verification scheme
for downloaded files (tarballs):
After buildgcc downloads a file or notices that it has already been
downloaded, it hashes the file, and compares the hash against the known
hash stored in util/crossgcc/sum/$filename.cksum. Two errors can occur:
1. The hash file is missing. In this case, crossgcc asks the user to
verify the authenticity of the downloaded file. It also calculates
its hash and stores it in util/crossgcc/sum/$filename.cksum.calc.
If the file is authentic, the user may rename the calculated hash
file to $filename.cksum, so that it can be found the next time
buildgcc is started.
2. The known hash and the calculated hash differ. This is the case that
this patch seeks to protect against, because it may imply that the
downloaded file was unexpectedly changed, either in transit
(Man-in-the-Middle attack) or on the file server that it was
downloaded from. If buildgcc detects such a hash mismatch, it asks
the user to delete the downloaded file and retry, because it can also
be caused by a benign network error. If, however, the error persists,
buildgcc can't continue without risking that the user runs malicious
code, and it stops.
Note: The hash algorithm may be changed in the future, but for now I
left it at SHA-1, to avoid bloating this patch.
Signed-off-by: Jonathan Neuschäfer <email@example.com>
Tested-by: build bot (Jenkins) <firstname.lastname@example.org>
Reviewed-by: Paul Menzel <email@example.com>
Reviewed-by: Patrick Georgi <firstname.lastname@example.org>
1 file changed