File u_Use-better-fallbacks-to-generate-cookies-if-arc4rand.patch of Package xorg-x11-server.27640
From 44a643812ce3c07cd38972abfa9dbd163529c192 Mon Sep 17 00:00:00 2001
From: Matthias Gerstner <mgerstner@suse.de>
Date: Thu, 13 Jul 2017 14:58:04 +0200
Subject: [PATCH] Use better fallbacks to generate cookies if arc4random_buf(3)
is unavailable
References: bsc#1025084
If arc4random_buf() is not available for generating cookies:
- use getentropy(), if available (which was only recently added to
glibc)
- use getrandom() via syscall(), if available (there was no glibc
wrapper for this syscall for a long time)
- if all else fails, directly read from /dev/urandom as before, but
employ O_CLOEXEC, do an OsAbort() in case the random data couldn't be
read to avoid unsecure situations. Don't know if that's too hard a
measure but it shouldn't actually occur except on maximum number of
FDs reached
Reviewed-by: Stefan Dirsch <sndirsch@suse.de>
---
configure.ac | 4 +-
include/dix-config.h.in | 6 +++
os/auth.c | 138 ++++++++++++++++++++++++++++++++++++++++++++++--
3 files changed, 141 insertions(+), 7 deletions(-)
Index: xorg-server-1.19.3/configure.ac
===================================================================
--- xorg-server-1.19.3.orig/configure.ac
+++ xorg-server-1.19.3/configure.ac
@@ -134,7 +134,7 @@ AM_CONDITIONAL(SPECIAL_DTRACE_OBJECTS, [
AC_HEADER_DIRENT
AC_HEADER_STDC
AC_CHECK_HEADERS([fcntl.h stdlib.h string.h unistd.h dlfcn.h stropts.h \
- fnmatch.h sys/mkdev.h sys/sysmacros.h sys/utsname.h])
+ fnmatch.h sys/mkdev.h sys/sysmacros.h sys/utsname.h sys/syscall.h])
dnl Checks for typedefs, structures, and compiler characteristics.
AC_C_CONST
@@ -226,7 +226,7 @@ AC_REPLACE_FUNCS([reallocarray strcasecm
AM_CONDITIONAL(POLL, [test "x$ac_cv_func_poll" = "xyes"])
AC_CHECK_LIB([bsd], [arc4random_buf])
-AC_CHECK_FUNCS([arc4random_buf])
+AC_CHECK_FUNCS([arc4random_buf getentropy])
AC_CHECK_DECLS([program_invocation_short_name], [], [], [[#include <errno.h>]])
Index: xorg-server-1.19.3/include/dix-config.h.in
===================================================================
--- xorg-server-1.19.3.orig/include/dix-config.h.in
+++ xorg-server-1.19.3/include/dix-config.h.in
@@ -167,6 +167,9 @@
/* Define to 1 if you have the `arc4random_buf' function. */
#undef HAVE_ARC4RANDOM_BUF
+/* Define to 1 if you have the `getentropy' function. */
+#undef HAVE_GETENTROPY
+
/* Define to use libc SHA1 functions */
#undef HAVE_SHA1_IN_LIBC
@@ -244,6 +247,9 @@
/* Define to 1 if you have the <sys/utsname.h> header file. */
#undef HAVE_SYS_UTSNAME_H
+/* Define to 1 if you have the <sys/syscall.h> header file. */
+#undef HAVE_SYS_SYSCALL_H
+
/* Define to 1 if you have the `timingsafe_memcmp' function. */
#undef HAVE_TIMINGSAFE_MEMCMP
Index: xorg-server-1.19.3/os/auth.c
===================================================================
--- xorg-server-1.19.3.orig/os/auth.c
+++ xorg-server-1.19.3/os/auth.c
@@ -48,6 +48,10 @@ from The Open Group.
#ifdef HAVE_LIBBSD
#include <bsd/stdlib.h> /* for arc4random_buf() */
#endif
+#include <errno.h>
+#ifdef HAVE_SYS_SYSCALL_H
+#include <syscall.h>
+#endif
struct protocol {
unsigned short name_length;
@@ -304,16 +308,140 @@ GenerateAuthorization(unsigned name_length,
#endif /* XCSECURITY */
+#if ! defined(HAVE_ARC4RANDOM_BUF)
+
+// fallback function to get random data directly from /dev/urandom
+
+static int
+GetUrandom ( char *buffer, size_t length )
+{
+ int random_fd = -1;
+ int res = -1;
+ size_t filled = 0;
+
+ // larger requests are typically rejected by getentropy() / getrandom()
+ // because they could block or return partially filled buffers
+ if( length > 256 ) {
+ errno = EIO;
+ return -1;
+ }
+
+ random_fd = open("/dev/urandom", O_RDONLY | O_CLOEXEC);
+
+ if( random_fd == -1 ) {
+ return -1;
+ }
+
+ while( filled < length ) {
+ res = read(random_fd, (char*)buffer + filled, length - filled);
+
+ if( res == -1 ) {
+ // shouldn't actually happen acc. to man(4) random,
+ // but you never know
+ if( errno == EINTR ) {
+ continue;
+ }
+
+ res = errno;
+ close(random_fd);
+ errno = res;
+ return -1;
+ }
+ else if( res == 0 ) {
+ close(random_fd);
+ // no more bytes available? should not happen
+ errno = EIO;
+ return -1;
+ }
+
+ filled += res;
+ }
+
+ close(random_fd);
+
+ return 0;
+}
+
+#endif // ! defined(HAVE_ARC4RANDOM_BUF)
+
+#if !defined(HAVE_GETENTROPY) && defined(HAVE_SYS_SYSCALL_H) && defined(SYS_getrandom)
+# define TRY_GETRANDOM
+#endif
+
+#ifdef TRY_GETRANDOM
+
+/*
+ * wrapper for the getrandom() syscall which was for a long time implemented
+ * in the Linux kernel, but not wrapped in glibc
+ */
+static int
+GetRandom ( char *buffer, size_t length )
+{
+ int res;
+ size_t filled = 0;
+
+ // larger requests are typically rejected by getentropy() / getrandom()
+ // because they could block or return partially filled buffers
+ if( length > 256 )
+ {
+ errno = EIO;
+ return -1;
+ }
+
+ while( filled < length )
+ {
+ /*
+ * glibc does not contain a syscall wrapper for this in older
+ * versions
+ */
+ res = syscall(SYS_getrandom, (char*)buffer + filled, length - filled, 0);
+
+ if( res == -1 )
+ {
+ if( errno == EINTR ) {
+ continue;
+ }
+
+ return -1;
+ }
+ else if( res == 0 )
+ {
+ // no more bytes available? should not happen
+ errno = EIO;
+ return -1;
+ }
+
+ filled += res;
+ }
+
+ return 0;
+}
+
+#endif /* TRY_GETRANDOM */
+
void
GenerateRandomData(int len, char *buf)
{
#ifdef HAVE_ARC4RANDOM_BUF
arc4random_buf(buf, len);
#else
- int fd;
+ int ret = -1;
+# ifdef HAVE_GETENTROPY
+ /* use getentropy instead */
+ ret = getentropy (buf, len);
+# elif defined(TRY_GETRANDOM)
+ /* try getrandom() wrapper */
+ ret = GetRandom(buf, len);
+# endif
+
+ if( ret == -1 ) {
+ // fallback to manual reading of /dev/urandom
+ ret = GetUrandom(buf, len);
+ }
- fd = open("/dev/urandom", O_RDONLY);
- read(fd, buf, len);
- close(fd);
-#endif
+ if( ret == -1 ) {
+ // no error return possible, rather abort than have security problems
+ OsAbort();
+ }
+#endif // HAVE_ARC4RANDOM_BUF
}
