util: introduce memmem_safe() and make use of it

GNU memmem() requires a nonnull first parameter. Let's introduce
memmem_safe() that removes this restriction for zero-length parameters,
and make use of it where appropriate.

http://lists.freedesktop.org/archives/systemd-devel/2015-May/031705.html

2 files changed, 16 insertions, 1 deletions

diff --git a/src/libsystemd/sd-bus/bus-socket.c b/src/libsystemd/sd-bus/bus-socket.c
index 94a5c04c8b..24b9c4d117 100644
--- a/src/libsystemd/sd-bus/bus-socket.c
+++ b/src/libsystemd/sd-bus/bus-socket.c
@@ -177,7 +177,7 @@ static int bus_socket_auth_verify_client(sd_bus *b) {
         /* We expect two response lines: "OK" and possibly
          * "AGREE_UNIX_FD" */
 
-        e = memmem(b->rbuffer, b->rbuffer_size, "\r\n", 2);
+        e = memmem_safe(b->rbuffer, b->rbuffer_size, "\r\n", 2);
         if (!e)
                 return 0;
 
diff --git a/src/shared/util.h b/src/shared/util.h
index 637934fecc..0c81e3dc45 100644
--- a/src/shared/util.h
+++ b/src/shared/util.h
@@ -787,6 +787,21 @@ static inline void qsort_safe(void *base, size_t nmemb, size_t size, comparison_
         qsort(base, nmemb, size, compar);
 }
 
+/* Normal memmem() requires haystack to be nonnull, which is annoying for zero-length buffers */
+static inline void *memmem_safe(const void *haystack, size_t haystacklen, const void *needle, size_t needlelen) {
+
+        if (needlelen <= 0)
+                return (void*) haystack;
+
+        if (haystacklen < needlelen)
+                return NULL;
+
+        assert(haystack);
+        assert(needle);
+
+        return memmem(haystack, haystacklen, needle, needlelen);
+}
+
 int proc_cmdline(char **ret);
 int parse_proc_cmdline(int (*parse_word)(const char *key, const char *value));
 int get_proc_cmdline_key(const char *parameter, char **value);