[Qemu-devel] [PATCH] Do not abort on qemu_malloc(0) in production builds

[Anthony Liguori]

qemu_malloc() does not allow size=0 to be passed in and aborts on this behavior.

Unfortunately, there is good reason to believe that within qemu, there are a
number of, so far, undetected places that assume size=0 can be safely passed.
Since we do not want to abort unnecessarily in production builds, return
qemu_malloc(1) whenever the version file indicates that this is a production
build.

Also introduce --enable-zero-malloc/--disable-zero-malloc to make this behavior
overridable.

Signed-off-by: Anthony Liguori <address@hidden>
---
 configure     |   24 +++++++++++++++++++++++-
 qemu-malloc.c |   17 +++++++++++++----
 2 files changed, 36 insertions(+), 5 deletions(-)

diff --git a/configure b/configure
index a29839e..ede820e 100755
--- a/configure
+++ b/configure
@@ -256,6 +256,7 @@ blobs="yes"
 pkgversion=""
 check_utests="no"
 user_pie="no"
+zero_malloc=""
 
 # OS specific
 if check_define __linux__ ; then
@@ -600,6 +601,10 @@ for opt do
   ;;
   --enable-docs) docs="yes"
   ;;
+  --enable-zero-malloc) zero_malloc="yes"
+  ;;
+  --disable-zero-malloc) zero_malloc="no"
+  ;;
   *) echo "ERROR: unknown option $opt"; show_help="yes"
   ;;
   esac
@@ -752,6 +757,8 @@ echo "  --enable-linux-aio       enable Linux AIO support"
 echo "  --enable-io-thread       enable IO thread"
 echo "  --disable-blobs          disable installing provided firmware blobs"
 echo "  --kerneldir=PATH         look for kernel includes in PATH"
+echo "  --enable-zero-malloc     allow allocations of zero size"
+echo "  --disable-zero-malloc    abort on allocations of zero size"
 echo ""
 echo "NOTE: The object files are built at the place where configure is 
launched"
 exit 1
@@ -1792,8 +1799,9 @@ fi
 
 # Consult white-list to determine whether to enable werror
 # by default.  Only enable by default for git builds
+z_version=`cut -f3 -d. $source_path/VERSION`
+
 if test -z "$werror" ; then
-    z_version=`cut -f3 -d. $source_path/VERSION`
     if test "$z_version" = "50" -a \
         "$linux" = "yes" ; then
         werror="yes"
@@ -1802,6 +1810,16 @@ if test -z "$werror" ; then
     fi
 fi
 
+# Disable zero malloc errors for official releases unless explicitly told to
+# enable/disable
+if test -z "$zero_malloc" ; then
+    if test "$z_version" = "50" ; then
+       zero_malloc="no"
+    else
+       zero_malloc="yes"
+    fi
+fi
+
 if test "$werror" = "yes" ; then
     QEMU_CFLAGS="-Werror $QEMU_CFLAGS"
 fi
@@ -2109,6 +2127,10 @@ fi
 
 echo "CONFIG_UNAME_RELEASE=\"$uname_release\"" >> $config_host_mak
 
+if test "$zero_malloc" = "yes" ; then
+  echo "CONFIG_ZERO_MALLOC=y" >> $config_host_mak
+fi
+
 # USB host support
 case "$usb" in
 linux)
diff --git a/qemu-malloc.c b/qemu-malloc.c
index 295d185..e82af26 100644
--- a/qemu-malloc.c
+++ b/qemu-malloc.c
@@ -42,21 +42,30 @@ void qemu_free(void *ptr)
     free(ptr);
 }
 
+static int allow_zero_malloc(void)
+{
+#if defined(CONFIG_ZERO_MALLOC)
+    return 1;
+#else
+    return 0;
+#endif
+}
+
 void *qemu_malloc(size_t size)
 {
-    if (!size) {
+    if (!size && !allow_zero_malloc()) {
         abort();
     }
-    return oom_check(malloc(size));
+    return oom_check(malloc(size ? size : 1));
 }
 
 void *qemu_realloc(void *ptr, size_t size)
 {
     if (size) {
         return oom_check(realloc(ptr, size));
-    } else {
+    } else if (allow_zero_malloc()) {
         if (ptr) {
-            return realloc(ptr, size);
+            return realloc(ptr, size ? size : 1);
         }
     }
     abort();
-- 
1.6.2.5