From ff5e59f32255913bb1cdf51441b98c9107ae165b Mon Sep 17 00:00:00 2001
From: Benjamin Tissoires <benjamin.tissoires@gmail.com>
Date: Tue, 4 Apr 2017 19:12:53 +0200
Subject: Use getentropy() if arc4random_buf() is not available
This allows to fix CVE-2017-2626 on Linux platforms without pulling in
libbsd.
The libc getentropy() is available since glibc 2.25 but also on OpenBSD.
For Linux, we need at least a v3.17 kernel. If the recommended
arc4random_buf() function is not available, emulate it by first trying
to use getentropy() on a supported glibc and kernel. If the call fails,
fall back to the current (partly vulnerable) code.
Signed-off-by: Benjamin Tissoires <benjamin.tissoires@gmail.com>
Reviewed-by: Mark Kettenis <kettenis@openbsd.org>
Reviewed-by: Alan Coopersmith <alan.coopersmith@oracle.com>
Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
---
configure.ac | 2 +-
src/iceauth.c | 65 ++++++++++++++++++++++++++++++++++++++++++-----------------
2 files changed, 47 insertions(+), 20 deletions(-)
diff --git a/configure.ac b/configure.ac
index 458882a..c971ab6 100644
--- a/configure.ac
+++ b/configure.ac
@@ -38,7 +38,7 @@ AC_DEFINE(ICE_t, 1, [Xtrans transport type])
# Checks for library functions.
AC_CHECK_LIB([bsd], [arc4random_buf])
-AC_CHECK_FUNCS([asprintf arc4random_buf])
+AC_CHECK_FUNCS([asprintf arc4random_buf getentropy])
# Allow checking code with lint, sparse, etc.
XORG_WITH_LINT
diff --git a/src/iceauth.c b/src/iceauth.c
index ed31683..de4785b 100644
--- a/src/iceauth.c
+++ b/src/iceauth.c
@@ -44,31 +44,19 @@ Author: Ralph Mor, X Consortium
static int was_called_state;
-/*
- * MIT-MAGIC-COOKIE-1 is a sample authentication method implemented by
- * the SI. It is not part of standard ICElib.
- */
+#ifndef HAVE_ARC4RANDOM_BUF
-
-char *
-IceGenerateMagicCookie (
+static void
+emulate_getrandom_buf (
+ char *auth,
int len
)
{
- char *auth;
-#ifndef HAVE_ARC4RANDOM_BUF
long ldata[2];
int seed;
int value;
int i;
-#endif
- if ((auth = malloc (len + 1)) == NULL)
- return (NULL);
-
-#ifdef HAVE_ARC4RANDOM_BUF
- arc4random_buf(auth, len);
-#else
#ifdef ITIMER_REAL
{
struct timeval now;
@@ -76,13 +64,13 @@ IceGenerateMagicCookie (
ldata[0] = now.tv_sec;
ldata[1] = now.tv_usec;
}
-#else
+#else /* ITIMER_REAL */
{
long time ();
ldata[0] = time ((long *) 0);
ldata[1] = getpid ();
}
-#endif
+#endif /* ITIMER_REAL */
seed = (ldata[0]) + (ldata[1] << 16);
srand (seed);
for (i = 0; i < len; i++)
@@ -90,7 +78,46 @@ IceGenerateMagicCookie (
value = rand ();
auth[i] = value & 0xff;
}
-#endif
+}
+
+static void
+arc4random_buf (
+ char *auth,
+ int len
+)
+{
+ int ret;
+
+#if HAVE_GETENTROPY
+ /* weak emulation of arc4random through the entropy libc */
+ ret = getentropy (auth, len);
+ if (ret == 0)
+ return;
+#endif /* HAVE_GETENTROPY */
+
+ emulate_getrandom_buf (auth, len);
+}
+
+#endif /* !defined(HAVE_ARC4RANDOM_BUF) */
+
+/*
+ * MIT-MAGIC-COOKIE-1 is a sample authentication method implemented by
+ * the SI. It is not part of standard ICElib.
+ */
+
+
+char *
+IceGenerateMagicCookie (
+ int len
+)
+{
+ char *auth;
+
+ if ((auth = malloc (len + 1)) == NULL)
+ return (NULL);
+
+ arc4random_buf (auth, len);
+
auth[len] = '\0';
return (auth);
}
--
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