rand_unix.c: open random devices on first use only
Commit c7504aeb (pr #6432) fixed a regression for applications in chroot environments, which compensated the fact that the new OpenSSL CSPRNG (based on the NIST DRBG) now reseeds periodically, which the previous one didn't. Now the reseeding could fail in the chroot environment if the DEVRANDOM devices were not present anymore and no other entropy source (e.g. getrandom()) was available. The solution was to keep the file handles for the DEVRANDOM devices open by default. In fact, the fix did more than this, it opened the DEVRANDOM devices early and unconditionally in rand_pool_init(), which had the unwanted side effect that the devices were opened (and kept open) even in cases when they were not used at all, for example when the getrandom() system call was available. Due to a bug (issue #7419) this even happened when the feature was disabled by the application. This commit removes the unconditional opening of all DEVRANDOM devices. They will now only be opened (and kept open) on first use. In particular, if getrandom() is available, the handles will not be opened unnecessarily. This change does not introduce a regression for applications compiled for libcrypto 1.1.0, because the SSLEAY RNG also seeds on first use. So in the above constellation the CSPRNG will only be properly seeded if it is happens before the forking and chrooting. Fixes #7419 Reviewed-by: Paul Dale <paul.dale@oracle.com> (Merged from https://github.com/openssl/openssl/pull/7437) (cherry picked from commit 8cfc1971)
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