util: Protect system calls against signals

Most system calls will fail if interrupted by a SIGALRM. Make sure we
block SIGALRM prior to do the syscall, and restore the set of signals
afterwards.

Signed-off-by: Olivier Fourdan <ofourdan@redhat.com>

src/util-io.c

@@ -47,7 +47,9 @@ xread_with_fds(int fd, void *buf, size_t count, int **fds)
 		.msg_controllen = sizeof(control),
 	};
 
+	sigset_t old_mask = signals_block();
 	int received = xerrno(recvmsg(fd, &msg, 0));
+	signals_release(old_mask);
 	if (received > 0) {
 		*fds = NULL;
 
@@ -110,7 +112,11 @@ xsend_with_fd(int fd, const void *buf, size_t len, int *fds)
 	header->cmsg_type = SCM_RIGHTS;
 	memcpy(CMSG_DATA(CMSG_FIRSTHDR(&msg)), fds, nfds * sizeof(int));
 
-	return xerrno(sendmsg(fd, &msg, MSG_NOSIGNAL));
+	sigset_t old_mask = signals_block();
+	int sent = xerrno(sendmsg(fd, &msg, MSG_NOSIGNAL));
+	signals_release(old_mask);
+
+	return sent;
 }
 
 /* consider this struct opaque */

src/util-io.h

@@ -43,7 +43,7 @@
 /**
  * Blocks the SIGALRM signal.
  *
- * @return the previous set of signals to pass to release_signals()
+ * @return the previous set of signals to pass to signals_release()
  */
 static inline sigset_t
 signals_block(void)
@@ -61,7 +61,7 @@ signals_block(void)
 /**
  * Release the SIGALRM signal.
  *
- * @param mask: The previous set of signals as returned by block_signals().
+ * @param mask: The previous set of signals as returned by signals_block().
  */
 static inline void
 signals_release(sigset_t mask)
@@ -81,12 +81,15 @@ xerrno(int value) {
 }
 
 /**
- * Wrapper around close(). It checks for fd != -1 to satisfy coverity and
- * friends and always returns -1.
+ * Wrapper around close() that blocks the SIGALRM signal. It checks for
+ * fd != -1 to satisfy coverity and friends and always returns -1.
  */
 static inline int
 xclose(int fd) {
+	sigset_t old_mask = signals_block();
 	if (fd != -1) close(fd);
+	signals_release(old_mask);
+
 	return -1;
 }
 
@@ -97,42 +100,56 @@ DEFINE_TRIVIAL_CLEANUP_FUNC(FILE *, fclose);
 #define _cleanup_fclose_ _cleanup_(fclosep)
 
 /**
- * Wrapper around read(). Returns the number of bytes read or a negative
- * errno on failure.
+ * Wrapper around read() that blocks the SIGALRM signal.
+ * Returns the number of bytes read or a negative  errno on failure.
  */
 static inline int
 xread(int fd, void *buf, size_t count)
 {
-	return xerrno(read(fd, buf, count));
+	sigset_t old_mask = signals_block();
+	int n = xerrno(read(fd, buf, count));
+	signals_release(old_mask);
+
+	return n;
 }
 
 /**
- * Wrapper around read(). Returns the number of bytes read or a negative
- * errno on failure. Any fds passed along with the message
- * are stored in the -1-terminated allocated fds array, to be freed by the
- * caller. Where no fds were passed, the array is NULL.
+ * Wrapper around read() that blocks the SIGALRM signal.
+ * Returns the number of bytes read or a negative errno on failure.
+ * Any fds passed along with the message are stored in the -1-terminated
+ * allocated fds array, to be freed by the caller. Where no fds were
+ * passed, the array is NULL.
  */
 int
 xread_with_fds(int fd, void *buf, size_t count, int **fds);
 
 /**
- * Wrapper around write(). Returns the number of bytes written or a negative
- * errno on failure.
+ * Wrapper around write() that blocks the SIGALRM signal.
+ * Returns the number of bytes written or a negative errno on failure.
  */
 static inline int
 xwrite(int fd, const void *buf, size_t count)
 {
-	return xerrno(write(fd, buf, count));
+	sigset_t old_mask = signals_block();
+	int n = xerrno(write(fd, buf, count));
+	signals_release(old_mask);
+
+	return n;
 }
 
 /**
- * Wrapper around send() that always sets MSG_NOSIGNAL. Returns the number
- * of bytes written or a negative errno on failure.
+ * Wrapper around send() that always sets MSG_NOSIGNAL and blocks the
+ * SIGALRM signal.
+ * Returns the number of bytes written or a negative errno on failure.
  */
 static inline int
 xsend(int fd, const void *buf, size_t len)
 {
-	return xerrno(send(fd, buf, len, MSG_NOSIGNAL));
+	sigset_t old_mask = signals_block();
+	int n = xerrno(send(fd, buf, len, MSG_NOSIGNAL));
+	signals_release(old_mask);
+
+	return n;
 }
 
 /**
@@ -158,14 +175,19 @@ xconnect(const char *path)
 	if (!xsnprintf(addr.sun_path, sizeof(addr.sun_path), "%s", path))
 		return -EINVAL;
 
+	sigset_t old_mask = signals_block();
 	int sockfd = socket(AF_UNIX, SOCK_STREAM|SOCK_NONBLOCK, 0);
 	if (sockfd == -1)
-		return -errno;
+		goto fail;
 
 	if (connect(sockfd, (struct sockaddr*)&addr, sizeof(addr)) == -1)
-		return -errno;
+		goto fail;
 
+	signals_release(old_mask);
 	return sockfd;
+fail:
+	signals_release(old_mask);
+	return -errno;
 }
 
 /**