Re: Move OpenSSL random under USE_OPENSSL_RANDOM

[Michael Paquier]

On Sun, Nov 15, 2020 at 12:16:56PM -0500, Tom Lane wrote:
> The obvious problem with this is that if !USE_OPENSSL, we will not have
> pulled in openssl's headers.

FWIW, I argued upthread against including this part because it is
useless: if not building with OpenSSL, we'll never have the base to be
able to use RAND_poll().

> However ... all these machines are pointing at line 96, which is not
> that one but the one under "#if defined(USE_OPENSSL)".  So I'm not sure
> what to make of that, except that a bit more finesse seems required.

The build scripts of src/tools/msvc/ choose to not use OpenSSL as
strong random source even if building with OpenSSL.  The top of the
file only includes openssl/rand.h if using USE_OPENSSL_RANDOM.

Thinking about that afresh, I think that we got that wrong here on
three points:
- If attempting to use OpenSSL on Windows, let's just bite the bullet
and use OpenSSL as random source, using Windows as source only when
not building with OpenSSL.
- Instead of using a call to RAND_poll() that we know will never work,
let's just issue a compilation failure if attempting to use
USE_OPENSSL_RANDOM without USE_OPENSSL.
- rand.h needs to be included under USE_OPENSSL.
--
Michael

diff --git a/src/port/pg_strong_random.c b/src/port/pg_strong_random.c
index 6d85f50b7c..c5dfe4b072 100644
--- a/src/port/pg_strong_random.c
+++ b/src/port/pg_strong_random.c
@@ -24,7 +24,7 @@
 #include <unistd.h>
 #include <sys/time.h>
 
-#ifdef USE_OPENSSL_RANDOM
+#ifdef USE_OPENSSL
 #include <openssl/rand.h>
 #endif
 #ifdef USE_WIN32_RANDOM
@@ -98,14 +98,11 @@ pg_strong_random_init(void)
 
 #if defined(USE_OPENSSL_RANDOM)
 	/*
-	 * In case the backend is using the PRNG from OpenSSL without being built
-	 * with support for OpenSSL, make sure to perform post-fork initialization.
-	 * If the backend is using OpenSSL then we have already performed this
-	 * step. The same version caveat as discussed in the comment above applies
-	 * here as well.
+	 * If attempting to use OpenSSL as random source without support for it,
+	 * consider this combination as invalid.
 	 */
 #ifndef USE_OPENSSL
-	RAND_poll();
+#error cannot use OpenSSL as random source without building with it.
 #endif
 
 #elif defined(USE_WIN32_RANDOM)
diff --git a/src/tools/msvc/Solution.pm b/src/tools/msvc/Solution.pm
index 17e480546c..cb01902ae9 100644
--- a/src/tools/msvc/Solution.pm
+++ b/src/tools/msvc/Solution.pm
@@ -525,6 +525,7 @@ sub GenerateFiles
 	if ($self->{options}->{openssl})
 	{
 		$define{USE_OPENSSL} = 1;
+		$define{USE_OPENSSL_RANDOM} = 1;
 
 		my ($digit1, $digit2, $digit3) = $self->GetOpenSSLVersion();
 

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