The pattern currently is to call get_cache(), generate the encoding
if that failed and then store it with cache(). The latter adopts the
passed encoding and frees any stored encoding. However, the latter means
that if two threads concurrently fail to get a cached encoding and then
both generate and store one, one of the threads might use an encoding
that was freed by the other thread.
Since encodings are not expected to change, we can avoid this issue by
not replacing an existing cache entry and instead return that (while
freeing the passed value instead of the cached one).
Closesstrongswan/strongswan#1231
This generalization allows the ring dimension n to be different
from the current n = 512 and allows kappa to be > 56. Also the
hash octets are consumed in a more consistent manner.
The c_indices derived from the SHA-512 random oracle consist of
nine bits (0..511). The leftmost 8 bits of each index are taken
on an octet-by-octet basis from the 56 leftmost octets of the
SHA-512 hash. The 9th bit needed for the LSB is taken from the
extra_bits 64 bit unsigned integer which consists of the 8 rightmost
octets of the SHA-512 hash (in network order). If more than 56
indices must be derived then additional rounds of the random oracle
are executed until all kappa c_indices have been determined.
The bug fix shifts the extra_bits value by one bit in each loop
iteration so that the LSB of each index is random. Also iterate
through the hash array using the loop variable j not the c_indices
variable i.
While these files are generated they don't really change and are not
architecture dependant. The previous solution prevented cross-compilation
from the repository as `bliss_huffman` was built for the target system but
was then executed on the build host to create the source files, which
naturally was bound to fail.
The `recreate-bliss-huffman` make target can be used inside the bliss
directory to update the source files if needed.
Fixes#812.
Coverity is still not happy when the result of an integer division is
assigned to a double (without e.g. casting the result to an int first to
indicate the intent). The shift should avoid this issue.
This requires moving test files so that the Makefile for the tests can be
included after building libstrongswan, which requires the plugin when
building monolithically. Due to this a static helper library is required
as directly referring to object files (or source files) is not possible.
It's also necessary to avoid any link-time dependency on libstrongswan in
bliss_huffman, to avoid circular dependencies (bliss_huffman -> libstrongswan
-> bliss -> bliss_huffman).
Theoretically, n could be zero and these variables are then used
uninitialized. Older GCC versions warn about this and on Travis where we
compile with -Werror this causes the tests to fail.
Tobias Brunner