random: use getrandom() on Linux where available
* random/rndlinux.c (_gcry_rndlinux_gather_random): use the getrandom() syscall on Linux if it exists, regardless of what kind of entropy was requested.
This change avoids the serious usability problem of unnecessary
blocking on /dev/random when the kernel's PRNG is already seeded,
without introducing the risk of pulling from an uninitialized PRNG.
It only has an effect on Linux systems with a functioning getrandom()
syscall. If that syscall is unavailable or fails, it should fall
through to the pre-existing behavior.
(cherry picked from commit 7e662680c170968661ee0105d132813f8281d229)
- GnuPG-bug-id: T3894
- Signed-off-by: Daniel Kahn Gillmor <firstname.lastname@example.org>