From a487cd4f8f56a9352eec1b6e05592a73794b162b Mon Sep 17 00:00:00 2001
From: "Yann E. MORIN" <yann.morin@orange.com>
Date: Tue, 10 Feb 2026 12:01:32 +0100
Subject: [PATCH] libcommon: check for getrandom()

Not all C libraries are glibc, or impersonating it; for example, musl
does not pretend to be any version of glibc. Thus, building on musl
fails when openssl is disabled, because no random-providing function is
detected, although musl does provide getrandom().

uClibc-ng on the other hand, can impersonate glibc, but availability of
getrandom() is not guatranteed there: getrandom() can be compiled out of
uClinbc-ng, or uClibc-ng can be too old to have it.

Add a configure-time check that getrandom() is available, as a fallback
when TLS is not enabled (and thus openssl is not used), and when not on
Win32 (where getting random numbers is always possible, at least from a
build perspective).

However, building with the plain Makefiles should keep working, so
slightly rework the defines checks in the code to account for the fact
that HAVE_GETRANDOM may already be defined at configure time.

Signed-off-by: Yann E. MORIN <yann.morin@orange.com>
---
 libcommon/CMakeLists.txt  |  8 ++++++++
 libcommon/random_common.c | 14 +++++++-------
 2 files changed, 15 insertions(+), 7 deletions(-)

diff --git a/libcommon/CMakeLists.txt b/libcommon/CMakeLists.txt
index 8d815566..fbea94c6 100644
--- a/libcommon/CMakeLists.txt
+++ b/libcommon/CMakeLists.txt
@@ -55,6 +55,14 @@ if (WITH_TLS)
 		PUBLIC
 			OpenSSL::SSL
 	)
+elseif(NOT WIN32)
+	include(CheckSymbolExists)
+	check_symbol_exists(getrandom "sys/random.h" GETRANDOM_FOUND)
+	if(GETRANDOM_FOUND)
+		add_definitions("-DHAVE_GETRANDOM")
+	else()
+		message(FATAL_ERROR "C library does not provide getrandom(); enable WITH_TLS instead")
+	endif()
 endif()
 
 if(INC_MEMTRACK)
diff --git a/libcommon/random_common.c b/libcommon/random_common.c
index 555bd801..e2c8d23a 100644
--- a/libcommon/random_common.c
+++ b/libcommon/random_common.c
@@ -26,18 +26,18 @@ Contributors:
 #  include <lmcons.h>
 #endif
 
-#if !defined(WITH_TLS) && defined(__linux__) && defined(__GLIBC__)
+#ifdef WITH_TLS
+#  include <openssl/bn.h>
+#  include <openssl/rand.h>
+#elif defined(HAVE_GETRANDOM)  /* From CMakeLists.txt */
+# include <sys/random.h>
+#elif defined(__linux__) && defined(__GLIBC__) /* For legacy Makefiles */
 #  if __GLIBC_PREREQ(2, 25)
 #    include <sys/random.h>
 #    define HAVE_GETRANDOM 1
 #  endif
 #endif
 
-#ifdef WITH_TLS
-#  include <openssl/bn.h>
-#  include <openssl/rand.h>
-#endif
-
 #include "mosquitto.h"
 
 
@@ -65,7 +65,7 @@ int mosquitto_getrandom(void *bytes, int count)
 	}
 
 	CryptReleaseContext(provider, 0);
-#else
+#else /* For legacy Makefiles */
 #  error "No suitable random function found."
 #endif
 	return rc;