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Do not pull libbsd, use getentropy or getrandom syscall instead

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This commit is contained in:
Benjamin Tissoires 2017-05-04 11:30:22 +02:00
parent 95dbfba828
commit c5f7dee5d7
4 changed files with 228 additions and 2 deletions
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90
0001-Use-getentropy-if-arc4random_buf-is-not-available.patch Normal file
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@ -0,0 +1,90 @@
From 0554324ec6bbc2071f5d1f8ad211a1643e29eb1f Mon Sep 17 00:00:00 2001
From: Benjamin Tissoires <benjamin.tissoires@gmail.com>
Date: Tue, 4 Apr 2017 19:13:38 +0200
Subject: [PATCH libXdmcp 1/3] Use getentropy() if arc4random_buf() is not
available
This allows to fix CVE-2017-2625 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 (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>
---
Key.c | 31 ++++++++++++++++++++++++++-----
configure.ac | 2 +-
2 files changed, 27 insertions(+), 6 deletions(-)
diff --git a/Key.c b/Key.c
index a09b316..70607d0 100644
--- a/Key.c
+++ b/Key.c
@@ -62,10 +62,11 @@ getbits (long data, unsigned char *dst)
#define getpid(x) _getpid(x)
#endif
-void
-XdmcpGenerateKey (XdmAuthKeyPtr key)
-{
#ifndef HAVE_ARC4RANDOM_BUF
+
+static void
+emulate_getrandom_buf (char *auth, int len)
+{
long lowbits, highbits;
srandom ((int)getpid() ^ time((Time_t *)0));
@@ -73,9 +74,29 @@ XdmcpGenerateKey (XdmAuthKeyPtr key)
highbits = random ();
getbits (lowbits, key->data);
getbits (highbits, key->data + 4);
-#else
+}
+
+static void
+arc4random_buf (void *auth, int len)
+{
+ int ret;
+
+#if HAVE_GETENTROPY
+ /* weak emulation of arc4random through the getentropy libc call */
+ ret = getentropy (auth, len);
+ if (ret == 0)
+ return;
+#endif /* HAVE_GETENTROPY */
+
+ emulate_getrandom_buf (auth, len);
+}
+
+#endif /* !defined(HAVE_ARC4RANDOM_BUF) */
+
+void
+XdmcpGenerateKey (XdmAuthKeyPtr key)
+{
arc4random_buf(key->data, 8);
-#endif
}
int
diff --git a/configure.ac b/configure.ac
index 2288502..d2b045d 100644
--- a/configure.ac
+++ b/configure.ac
@@ -65,7 +65,7 @@ esac
# Checks for library functions.
AC_CHECK_LIB([bsd], [arc4random_buf])
-AC_CHECK_FUNCS([srand48 lrand48 arc4random_buf])
+AC_CHECK_FUNCS([srand48 lrand48 arc4random_buf getentropy])
# Obtain compiler/linker options for depedencies
PKG_CHECK_MODULES(XDMCP, xproto)
--
2.9.3

53
0002-Fix-compilation-error-when-arc4random_buf-is-not-ava.patch Normal file
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@ -0,0 +1,53 @@
From 95bef09f135a70ba1174a0021f441b0bb62a9bec Mon Sep 17 00:00:00 2001
From: Benjamin Tissoires <benjamin.tissoires@gmail.com>
Date: Thu, 4 May 2017 11:05:15 +0200
Subject: [PATCH libXdmcp 2/3] Fix compilation error when arc4random_buf is not
available
Not sure how I missed that, but I did.
Also rename emulate_getrandom_buf() into insecure_getrandom_buf() as
requested in the previous patch reviews.
Last, getbits() expects an unsigned char, so remove the warning.
Signed-off-by: Benjamin Tissoires <benjamin.tissoires@gmail.com>
---
Key.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)
diff --git a/Key.c b/Key.c
index 70607d0..d61ad0e 100644
--- a/Key.c
+++ b/Key.c
@@ -65,15 +65,15 @@ getbits (long data, unsigned char *dst)
#ifndef HAVE_ARC4RANDOM_BUF
static void
-emulate_getrandom_buf (char *auth, int len)
+insecure_getrandom_buf (unsigned char *auth, int len)
{
long lowbits, highbits;
srandom ((int)getpid() ^ time((Time_t *)0));
lowbits = random ();
highbits = random ();
- getbits (lowbits, key->data);
- getbits (highbits, key->data + 4);
+ getbits (lowbits, auth);
+ getbits (highbits, auth + 4);
}
static void
@@ -88,7 +88,7 @@ arc4random_buf (void *auth, int len)
return;
#endif /* HAVE_GETENTROPY */
- emulate_getrandom_buf (auth, len);
+ insecure_getrandom_buf (auth, len);
}
#endif /* !defined(HAVE_ARC4RANDOM_BUF) */
--
2.9.3

74
0003-Add-getentropy-emulation-through-syscall.patch Normal file
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@ -0,0 +1,74 @@
From 4e166987d7e7d37d1f5cc71c0eb7918dea4fe443 Mon Sep 17 00:00:00 2001
From: Benjamin Tissoires <benjamin.tissoires@gmail.com>
Date: Thu, 4 May 2017 11:13:51 +0200
Subject: [PATCH libXdmcp 3/3] Add getentropy emulation through syscall
RHEL/f24/f25 only patch
Signed-off-by: Benjamin Tissoires <benjamin.tissoires@gmail.com>
---
Key.c | 48 ++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 48 insertions(+)
diff --git a/Key.c b/Key.c
index d61ad0e..4b0e9c0 100644
--- a/Key.c
+++ b/Key.c
@@ -76,6 +76,54 @@ insecure_getrandom_buf (unsigned char *auth, int len)
getbits (highbits, auth + 4);
}
+#ifndef HAVE_GETENTROPY
+#include <sys/syscall.h>
+#include <errno.h>
+
+/* code taken from libressl, license: */
+/*
+ * Copyright (c) 2014 Theo de Raadt <deraadt@openbsd.org>
+ * Copyright (c) 2014 Bob Beck <beck@obtuse.com>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ *
+ * Emulation of getentropy(2) as documented at:
+ * http://man.openbsd.org/getentropy.2
+ */
+#ifdef __NR_getrandom
+
+static int
+getentropy(void *buf, size_t len)
+{
+ int pre_errno = errno;
+ int ret;
+ if (len > 256)
+ return (-1);
+ do {
+ ret = syscall(__NR_getrandom, buf, len, 0);
+ } while (ret == -1 && errno == EINTR);
+
+ if (ret != len)
+ return (-1);
+ errno = pre_errno;
+
+ return (0);
+}
+#define HAVE_GETENTROPY 1
+#endif /* __NR_getrandom */
+
+#endif /* HAVE_GETENTROPY */
+
static void
arc4random_buf (void *auth, int len)
{
--
2.9.3

13
libXdmcp.spec
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@ -1,7 +1,7 @@
Summary: X Display Manager Control Protocol library
Name: libXdmcp
Version: 1.1.2
Release: 5%{?dist}
Release: 6%{?dist}
License: MIT
Group: System Environment/Libraries
URL: http://www.x.org
@ -12,7 +12,10 @@ BuildRequires: xorg-x11-util-macros
BuildRequires: autoconf automake libtool
BuildRequires: xorg-x11-proto-devel
BuildRequires: xmlto
BuildRequires: libbsd-devel
Patch0: 0001-Use-getentropy-if-arc4random_buf-is-not-available.patch
Patch1: 0002-Fix-compilation-error-when-arc4random_buf-is-not-ava.patch
Patch2: 0003-Add-getentropy-emulation-through-syscall.patch
%description
X Display Manager Control Protocol library.
@ -27,6 +30,9 @@ libXdmcp development package.
%prep
%setup -q
%patch0 -p1 -b .cve-2017-2625
%patch1 -p1 -b .cve-2017-2625
%patch2 -p1 -b .cve-2017-2625
%build
autoreconf -v --install --force
@ -64,6 +70,9 @@ rm -rf $RPM_BUILD_ROOT
%{_libdir}/pkgconfig/xdmcp.pc
%changelog
* Tue Mar 28 2017 Benjamin Tissoires <benjamin.tissoires@redhat.com> 1.1.2-6
- Do not pull libbsd, use getentropy or getrandom syscall instead
* Wed Mar 01 2017 Benjamin Tissoires <benjamin.tissoires@redhat.com> 1.1.2-5
- Use libbsd for randoms (CVE-2017-2625, rhbz#1427716)