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List:       busybox
Subject:    [PATCH v4] miscutils/seedrng.c: fix <sys/random.h> include error on glibc < 2.25
From:       Thomas Devoogdt <thomas () devoogdt ! com>
Date:       2023-02-18 12:32:36
Message-ID: 20230218123236.1210239-1-thomas () devoogdt ! com
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From: Thomas Devoogdt <thomas.devoogdt@barco.com>

getrandom() was introduced in version 3.17 of the Linux kernel.
       Support was added to glibc in version 2.25.

https://man7.org/linux/man-pages/man2/getrandom.2.html

read_new_seed will anyway fallback to /dev/{u}random if (ret != len)

Signed-off-by: Thomas Devoogdt <thomas.devoogdt@barco.com>
---
v2:
 - check if __GLIBC_PREREQ is defined
 - assume by default that we have <sys/random.h>
v3:
 - errno was not set, so is_creditable was never true
v4:
 - fixed some whitespaces
---
 miscutils/seedrng.c | 24 +++++++++++++++++++-----
 1 file changed, 19 insertions(+), 5 deletions(-)

diff --git a/miscutils/seedrng.c b/miscutils/seedrng.c
index 967741dc7..0091e63e9 100644
--- a/miscutils/seedrng.c
+++ b/miscutils/seedrng.c
@@ -42,12 +42,21 @@
 #include "libbb.h"
 
 #include <linux/random.h>
-#include <sys/random.h>
 #include <sys/file.h>
 
+#define HAVE_SYS_RANDOM_H 1
+#if defined(__GLIBC_PREREQ)
+#if !__GLIBC_PREREQ(2, 25)
+#undef HAVE_SYS_RANDOM_H
+#endif
+#endif
+
+#if defined(HAVE_SYS_RANDOM_H)
+#include <sys/random.h>
 #ifndef GRND_INSECURE
 #define GRND_INSECURE 0x0004 /* Apparently some headers don't ship with this yet. */
 #endif
+#endif
 
 #define DEFAULT_SEED_DIR         "/var/lib/seedrng"
 #define CREDITABLE_SEED_NAME     "seed.credit"
@@ -81,13 +90,15 @@ static size_t determine_optimal_seed_len(void)
 static bool read_new_seed(uint8_t *seed, size_t len)
 {
 	bool is_creditable;
-	ssize_t ret;
 
-	ret = getrandom(seed, len, GRND_NONBLOCK);
+#if defined(HAVE_SYS_RANDOM_H)
+	ssize_t ret = getrandom(seed, len, GRND_NONBLOCK);
 	if (ret == (ssize_t)len) {
 		return true;
 	}
-	if (ret < 0 && errno == ENOSYS) {
+	if (ret < 0 && errno == ENOSYS)
+#endif
+	{
 		int fd = xopen("/dev/random", O_RDONLY);
 		struct pollfd random_fd;
 		random_fd.fd = fd;
@@ -96,11 +107,14 @@ static bool read_new_seed(uint8_t *seed, size_t len)
 //This is racy. is_creditable can be set to true here, but other process
 //can consume "good" random data from /dev/urandom before we do it below.
 		close(fd);
-	} else {
+	}
+#if defined(HAVE_SYS_RANDOM_H)
+	else {
 		if (getrandom(seed, len, GRND_INSECURE) == (ssize_t)len)
 			return false;
 		is_creditable = false;
 	}
+#endif
 
 	/* Either getrandom() is not implemented, or
 	 * getrandom(GRND_INSECURE) did not give us LEN bytes.
-- 
2.34.1

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