From: Michael Jeanson <mjeanson@efficios.com>
Date: Thu, 15 Oct 2015 18:55:40 +0000 (-0400)
Subject: Port: Add compat for platforms with no MSG_NOSIGNAL or SO_NOSIGPIPE
X-Git-Tag: v2.8.0-rc1~262
X-Git-Url: https://git.lttng.org/?p=lttng-tools.git;a=commitdiff_plain;h=fbb1fd3a999509ca90c49577e53a47c23433d6f5

Port: Add compat for platforms with no MSG_NOSIGNAL or SO_NOSIGPIPE

Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
---

diff --git a/src/common/compat/socket.h b/src/common/compat/socket.h
index 5a6802aac..78610957b 100644
--- a/src/common/compat/socket.h
+++ b/src/common/compat/socket.h
@@ -23,6 +23,91 @@
 
 #include <common/macros.h>
 
+#ifndef MSG_NOSIGNAL
+# ifdef SO_NOSIGPIPE
+#   define MSG_NOSIGNAL SO_NOSIGPIPE
+# endif
+#endif
+
+#if defined(MSG_NOSIGNAL)
+static inline
+ssize_t lttng_recvmsg_nosigpipe(int sockfd, struct msghdr *msg)
+{
+	return recvmsg(sockfd, msg, MSG_NOSIGNAL);
+}
+#else
+
+#include <signal.h>
+#include <errno.h>
+
+static inline
+ssize_t lttng_recvmsg_nosigpipe(int sockfd, struct msghdr *msg)
+{
+	ssize_t received;
+	int saved_err;
+	sigset_t sigpipe_set, pending_set, old_set;
+	int sigpipe_was_pending;
+
+	/*
+	 * Discard the SIGPIPE from send(), not disturbing any SIGPIPE
+	 * that might be already pending. If a bogus SIGPIPE is sent to
+	 * the entire process concurrently by a malicious user, it may
+	 * be simply discarded.
+	 */
+	if (sigemptyset(&pending_set)) {
+		return -1;
+	}
+	/*
+	 * sigpending returns the mask of signals that are _both_
+	 * blocked for the thread _and_ pending for either the thread or
+	 * the entire process.
+	 */
+	if (sigpending(&pending_set)) {
+		return -1;
+	}
+	sigpipe_was_pending = sigismember(&pending_set, SIGPIPE);
+	/*
+	 * If sigpipe was pending, it means it was already blocked, so
+	 * no need to block it.
+	 */
+	if (!sigpipe_was_pending) {
+		if (sigemptyset(&sigpipe_set)) {
+			return -1;
+		}
+		if (sigaddset(&sigpipe_set, SIGPIPE)) {
+			return -1;
+		}
+		if (pthread_sigmask(SIG_BLOCK, &sigpipe_set, &old_set)) {
+			return -1;
+		}
+	}
+
+	/* Send and save errno. */
+	received = recvmsg(sockfd, msg, 0);
+	saved_err = errno;
+
+	if (received == -1 && errno == EPIPE && !sigpipe_was_pending) {
+		struct timespec timeout = { 0, 0 };
+		int ret;
+
+		do {
+			ret = sigtimedwait(&sigpipe_set, NULL,
+				&timeout);
+		} while (ret == -1 && errno == EINTR);
+	}
+	if (!sigpipe_was_pending) {
+		if (pthread_sigmask(SIG_SETMASK, &old_set, NULL)) {
+			return -1;
+		}
+	}
+	/* Restore send() errno */
+	errno = saved_err;
+
+	return received;
+}
+#endif
+
+
 #ifdef __linux__
 
 #define LTTNG_SOCK_CREDS SCM_CREDENTIALS
diff --git a/src/common/sessiond-comm/unix.c b/src/common/sessiond-comm/unix.c
index cf2c17ff7..5e0ba6281 100644
--- a/src/common/sessiond-comm/unix.c
+++ b/src/common/sessiond-comm/unix.c
@@ -182,7 +182,7 @@ ssize_t lttcomm_recv_unix_sock(int sock, void *buf, size_t len)
 
 	do {
 		len_last = iov[0].iov_len;
-		ret = recvmsg(sock, &msg, MSG_NOSIGNAL);
+		ret = lttng_recvmsg_nosigpipe(sock, &msg);
 		if (ret > 0) {
 			iov[0].iov_base += ret;
 			iov[0].iov_len -= ret;