Yes, I suck. This commit contains two totally unrelated changes and I really

should commit them seperately, but I am ignoring my own rules, and do it in a
single commit. I suck. I really do. I am sorry. Please don't try this at home.
And please don't tell your children!

* Show properly that avahi-autoipd is not built if libdaemon is missing (Closes #133)

* Enable stack-smashing protection if available and wokring. Patch from tedp. (Closes #105)



git-svn-id: file:///home/lennart/svn/public/avahi/trunk@1440 941a03a8-eaeb-0310-b9a0-b1bbd8fe43fe

2 files changed, 109 insertions, 10 deletions

diff --git a/common/gcc_stack_protect.m4 b/common/gcc_stack_protect.m4
index 616101e..13c5e0a 100644
--- a/common/gcc_stack_protect.m4
+++ b/common/gcc_stack_protect.m4
@@ -6,19 +6,23 @@ dnl     * Stricter language checking (C or C++)
 dnl     * Adds GCC_STACK_PROTECT_LIB to add -lssp to LDFLAGS as necessary
 dnl     * Caches all results
 dnl     * Uses macros to ensure correct ouput in quiet/silent mode
+dnl 1.2 - April 2007 - Ted Percival <ted@midg3t.net>
+dnl     * Added GCC_STACK_PROTECTOR macro for simpler (one-line) invocation
+dnl     * GCC_STACK_PROTECT_LIB now adds -lssp to LIBS rather than LDFLAGS
 dnl
 dnl About ssp:
 dnl GCC extension for protecting applications from stack-smashing attacks
 dnl http://www.research.ibm.com/trl/projects/security/ssp/
 dnl
 dnl Usage:
-dnl Call GCC_STACK_PROTECT_LIB to determine if the library implementing SSP is
-dnl available, then the appropriate C or C++ language's test. If you are using
-dnl both C and C++ you will need to use AC_LANG_PUSH and AC_LANG_POP to ensure
-dnl the right language is being used for each test.
+dnl Most people will simply call GCC_STACK_PROTECTOR.
+dnl If you only use one of C or C++, you can save time by only calling the
+dnl macro appropriate for that language. In that case you should also call
+dnl GCC_STACK_PROTECT_LIB first.
 dnl
-dnl GCC_STACK_PROTECT_LIB
-dnl adds libssp to the LDFLAGS if it is available
+dnl GCC_STACK_PROTECTOR
+dnl Tries to turn on stack protection for C and C++ by calling the following
+dnl three macros with the right languages.
 dnl
 dnl GCC_STACK_PROTECT_CC
 dnl checks -fstack-protector with the C compiler, if it exists then updates
@@ -28,16 +32,22 @@ dnl GCC_STACK_PROTECT_CXX
 dnl checks -fstack-protector with the C++ compiler, if it exists then updates
 dnl CXXFLAGS and defines ENABLE_SSP_CXX
 dnl
+dnl GCC_STACK_PROTECT_LIB
+dnl adds -lssp to LIBS if it is available
+dnl ssp is usually provided as part of libc, but was previously a separate lib
+dnl It does not hurt to add -lssp even if libc provides SSP - in that case
+dnl libssp will simply be ignored.
+dnl
 
 AC_DEFUN([GCC_STACK_PROTECT_LIB],[
   AC_CACHE_CHECK([whether libssp exists], ssp_cv_lib,
-    [ssp_old_ldflags="$LDFLAGS"
-     LDFLAGS="$LDFLAGS -lssp"
+    [ssp_old_libs="$LIBS"
+     LIBS="$LIBS -lssp"
      AC_TRY_LINK(,, ssp_cv_lib=yes, ssp_cv_lib=no)
-     LDFLAGS="$ssp_old_ldflags"
+     LIBS="$ssp_old_libs"
     ])
   if test $ssp_cv_lib = yes; then
-    LDFLAGS="$LDFLAGS -lssp"
+    LIBS="$LIBS -lssp"
   fi
 ])
 
@@ -75,3 +85,15 @@ AC_DEFUN([GCC_STACK_PROTECT_CXX],[
   fi
 ])
 
+AC_DEFUN([GCC_STACK_PROTECTOR],[
+  GCC_STACK_PROTECT_LIB
+
+  AC_LANG_PUSH([C])
+  GCC_STACK_PROTECT_CC
+  AC_LANG_POP([C])
+
+  AC_LANG_PUSH([C++])
+  GCC_STACK_PROTECT_CXX
+  AC_LANG_POP([C++])
+])
+
diff --git a/configure.ac b/configure.ac
index d9d4f42..81954a3 100644
--- a/configure.ac
+++ b/configure.ac
@@ -56,6 +56,79 @@ AC_PROG_LN_S
 AC_PROG_MAKE_SET
 AC_PROG_GCC_TRADITIONAL
 
+# -fstack-protector
+AC_ARG_ENABLE([stack-protector],
+    [AS_HELP_STRING([--disable-stack-protector],
+        [Disable GCC's/libc's stack-smashing protection])],
+    [case "${enableval}" in
+         yes) enable_ssp=yes ;;
+          no) enable_ssp=no ;;
+           *) AC_MSG_ERROR([invalid value ${enableval} for --disable-stack-protector]) ;;
+     esac],
+    [enable_ssp=yes])
+
+if test x"$enable_ssp" = x"yes" && test x"$GCC" != x"yes"; then
+    AC_MSG_NOTICE([Disabling stack-smashing protection because compiler is not GCC])
+    enable_ssp=no
+fi
+
+if test x"$enable_ssp" = x"yes"; then
+    # Check for broken ssp in libc: http://www.avahi.org/ticket/105
+    # libc's brokenness will get in the way regardless of whether -lssp is
+    # provided, but provide it anyway (otherwise non-libc ssp would wrongly
+    # break here)
+
+    # Get -lssp if it exists
+    GCC_STACK_PROTECT_LIB
+
+    AC_MSG_CHECKING([whether stack-smashing protection is available])
+    ssp_old_cflags="$CFLAGS"
+    ssp_old_ldflags="$LDFLAGS"
+    CFLAGS="$CFLAGS -fstack-protector-all -fPIC"
+    LDFLAGS="$LDFLAGS -Wl,-z,defs"
+    cat confdefs.h > conftest.c
+    cat >>conftest.c <<_ACEOF
+void test_broken_ssp(c)
+    const char *c;
+{
+    char arr[[123]], *p; /* beware of possible double-braces if copying this */
+    for (p = arr; *c; ++p) {
+        *p = *c;
+        ++c;
+    }
+}
+_ACEOF
+    rm -f conftest.o
+
+    if $CC -c $CFLAGS $CPPFLAGS -o conftest.o conftest.c >/dev/null 2>&1; then
+        AC_MSG_RESULT([yes])
+        AC_MSG_CHECKING([whether stack-smashing protection is buggy])
+        if $CC -o conftest.so $LDFLAGS -shared conftest.o $LIBS >/dev/null 2>&1; then
+            AC_MSG_RESULT([no])
+        else
+            AC_MSG_RESULT([yes])
+            enable_ssp=no
+        fi
+    else
+        AC_MSG_RESULT([no])
+    fi
+
+    rm -f conftest.c conftest.o conftest.so
+
+    CFLAGS="$ssp_old_cflags"
+    LDFLAGS="$ssp_old_ldflags"
+fi
+
+if test x"$enable_ssp" = x"yes"; then
+    # Do this the long way so we don't call GCC_STACK_PROTECT_LIB twice
+    GCC_STACK_PROTECT_CC
+
+    AC_LANG_PUSH([C++])
+    GCC_STACK_PROTECT_CXX
+    AC_LANG_POP([C++])
+    # XXX: Update the enable_ssp value now for output later?
+fi
+
 # libtool stuff
 AC_PROG_LIBTOOL
 
@@ -959,6 +1032,7 @@ echo "
     Group for avahi-autoipd:                   ${AVAHI_AUTOIPD_GROUP}
     Enable chroot():                           ${enable_chroot}
     Enable Linux inotify:                      ${have_inotify}
+    Enable stack-smashing protection:          ${enable_ssp}
 "
 
 BUILD_DAEMON="no   (You need libdaemon and expat!)"
@@ -985,6 +1059,9 @@ fi
 if test "x$ENABLE_COMPAT_HOWL" = "xyes" -a "x$BUILD_CLIENT" != "xyes" ; then
    ENABLE_COMPAT_HOWL="no   (You need libavahi-client!)"
 fi
+if test "x$ENABLE_AUTOIPD" = "xyes" -a "x$HAVE_LIBDAEMON" != "xyes" ; then
+   ENABLE_AUTOIPD="no   (You need libdaemon!)"
+fi
 
 BUILD_UI="no"
 if test "x$HAVE_GTK" = "xyes" -a "x$BUILD_CLIENT" = "xyes" ; then