util: Consolidate and improve workarounds for clang-tidy issue 58992

We have several workarounds for a clang-tidy bug where the checker doesn't
recognize that a number of system calls write to - and therefore initialise
- a socket address.  We can't neatly use a suppression, because the bogus
warning shows up some time after the actual system call, when we access
a field of the socket address which clang-tidy erroneously thinks is
uninitialised.

Consolidate these workarounds into one place by using macros to implement
wrappers around affected system calls which add a memset() of the sockaddr
to silence clang-tidy.  This removes the need for the individual memset()
workarounds at the callers - and the somewhat longwinded explanatory
comments.

We can then use a #define to not include the hack in "real" builds, but
only consider it for clang-tidy.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

Makefile

@@ -276,7 +276,7 @@ clang-tidy: $(SRCS) $(HEADERS)
 	-concurrency-mt-unsafe,\
 	-readability-identifier-length \
 	-config='{CheckOptions: [{key: bugprone-suspicious-string-compare.WarnOnImplicitComparison, value: "false"}]}' \
-	--warnings-as-errors=* $(SRCS) -- $(filter-out -pie,$(FLAGS) $(CFLAGS) $(CPPFLAGS))
+	--warnings-as-errors=* $(SRCS) -- $(filter-out -pie,$(FLAGS) $(CFLAGS) $(CPPFLAGS)) -DCLANG_TIDY_58992
 
 SYSTEM_INCLUDES := /usr/include $(wildcard /usr/include/$(TARGET))
 ifeq ($(shell $(CC) -v 2>&1 | grep -c "gcc version"),1)

icmp.c

@@ -76,11 +76,6 @@ void icmp_sock_handler(const struct ctx *c, union epoll_ref ref)
 	if (c->no_icmp)
 		return;
 
-	/* FIXME: Workaround clang-tidy not realizing that recvfrom()
-	 * writes the socket address.  See
-	 * https://github.com/llvm/llvm-project/issues/58992
-	 */
-	memset(&sr, 0, sizeof(sr));
 	n = recvfrom(ref.fd, buf, sizeof(buf), 0, (struct sockaddr *)&sr, &sl);
 	if (n < 0)
 		return;

tcp.c

@@ -2752,19 +2752,13 @@ void tcp_listen_handler(struct ctx *c, union epoll_ref ref,
 			const struct timespec *now)
 {
 	struct sockaddr_storage sa;
+	socklen_t sl = sizeof(sa);
 	union tcp_conn *conn;
-	socklen_t sl;
 	int s;
 
 	if (c->no_tcp || c->tcp.conn_count >= TCP_MAX_CONNS)
 		return;
 
-	sl = sizeof(sa);
-	/* FIXME: Workaround clang-tidy not realizing that accept4()
-	 * writes the socket address.  See
-	 * https://github.com/llvm/llvm-project/issues/58992
-	 */
-	memset(&sa, 0, sizeof(struct sockaddr_in6));
 	s = accept4(ref.fd, (struct sockaddr *)&sa, &sl, SOCK_NONBLOCK);
 	if (s < 0)
 		return;

util.h

@@ -9,6 +9,7 @@
 #include <stdlib.h>
 #include <stdarg.h>
 #include <stdbool.h>
+#include <string.h>
 
 #include "log.h"
 
@@ -225,4 +226,44 @@ int __daemon(int pidfile_fd, int devnull_fd);
 int fls(unsigned long x);
 int write_file(const char *path, const char *buf);
 
+/*
+ * Workarounds for https://github.com/llvm/llvm-project/issues/58992
+ *
+ * For a number (maybe all) system calls that _write_ a socket address,
+ * clang-tidy doesn't register that the memory of the socket address will be
+ * initialised after the call.  This can't easily be worked around with
+ * clang-tidy suppressions, because the warning doesn't show on the syscall
+ * itself but later when we access the supposedly uninitialised field.
+ */
+static inline void sa_init(struct sockaddr *sa, socklen_t *sl)
+{
+#ifdef CLANG_TIDY_58992
+	if (sa)
+		memset(sa, 0, *sl);
+#else
+	(void)sa;
+	(void)sl;
+#endif /* CLANG_TIDY_58992 */
+}
+
+static inline ssize_t wrap_recvfrom(int sockfd, void *buf, size_t len,
+				    int flags,
+				    struct sockaddr *src_addr,
+				    socklen_t *addrlen)
+{
+	sa_init(src_addr, addrlen);
+	return recvfrom(sockfd, buf, len, flags, src_addr, addrlen);
+}
+#define recvfrom(s, buf, len, flags, src, addrlen)		\
+	wrap_recvfrom((s), (buf), (len), (flags), (src), (addrlen))
+
+static inline int wrap_accept4(int sockfd, struct sockaddr *addr,
+			       socklen_t *addrlen, int flags)
+{
+	sa_init(addr, addrlen);
+	return accept4(sockfd, addr, addrlen, flags);
+}
+#define accept4(s, addr, addrlen, flags) \
+	wrap_accept4((s), (addr), (addrlen), (flags))
+
 #endif /* UTIL_H */