From 549df04044855ca170838fe2f7d92b523445be65 Mon Sep 17 00:00:00 2001
From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Date: Wed, 26 Aug 2015 18:24:11 -0400
Subject: [PATCH] Fix: close socket on protocol error, sendmsg MSG_NOSIGNAL

Don't try to keep interacting with sessiond when a protocol error is
detected at the UST application side: this means we cannot trust the
protocol anymore, so there is no reason for keeping the socket open.
For instance, if the application is exiting and we receive a new stream,
we're effectively not reading the stream data, and we return an error.
Unfortunately, the session daemon may try to send us another command,
but we will try interpreting the stream data as a command, which is
invalid.

Also, use MSG_NOSIGNAL flag in the fds recvmsg, so the session daemon
don't get killed with SIGPIPE when it cannot send to the socket due to
connection closed.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
---
 liblttng-ust-comm/lttng-ust-comm.c |  2 +-
 liblttng-ust/lttng-ust-comm.c      | 27 ++++++++++++++++-----------
 2 files changed, 17 insertions(+), 12 deletions(-)

diff --git a/liblttng-ust-comm/lttng-ust-comm.c b/liblttng-ust-comm/lttng-ust-comm.c
index 751ad2e3..6edb395f 100644
--- a/liblttng-ust-comm/lttng-ust-comm.c
+++ b/liblttng-ust-comm/lttng-ust-comm.c
@@ -390,7 +390,7 @@ ssize_t ustcomm_send_fds_unix_sock(int sock, int *fds, size_t nb_fd)
 	msg.msg_iovlen = 1;
 
 	do {
-		ret = sendmsg(sock, &msg, 0);
+		ret = sendmsg(sock, &msg, MSG_NOSIGNAL);
 	} while (ret < 0 && errno == EINTR);
 	if (ret < 0) {
 		/*
diff --git a/liblttng-ust/lttng-ust-comm.c b/liblttng-ust/lttng-ust-comm.c
index d48cc336..fbdee7d3 100644
--- a/liblttng-ust/lttng-ust-comm.c
+++ b/liblttng-ust/lttng-ust-comm.c
@@ -573,13 +573,13 @@ int handle_message(struct sock_info *sock_info,
 
 	if (ust_lock()) {
 		ret = -LTTNG_UST_ERR_EXITING;
-		goto end;
+		goto error;
 	}
 
 	ops = objd_ops(lum->handle);
 	if (!ops) {
 		ret = -ENOENT;
-		goto end;
+		goto error;
 	}
 
 	switch (lum->cmd) {
@@ -640,12 +640,12 @@ int handle_message(struct sock_info *sock_info,
 				}
 				ret = len;
 				free(bytecode);
-				goto end;
+				goto error;
 			} else {
 				DBG("incorrect filter data message size: %zd", len);
 				ret = -EINVAL;
 				free(bytecode);
-				goto end;
+				goto error;
 			}
 		}
 		bytecode->bc.len = lum->u.filter.data_size;
@@ -705,12 +705,12 @@ int handle_message(struct sock_info *sock_info,
 				}
 				ret = len;
 				free(node);
-				goto end;
+				goto error;
 			} else {
 				DBG("Incorrect exclusion data message size: %zd", len);
 				ret = -EINVAL;
 				free(node);
-				goto end;
+				goto error;
 			}
 		}
 		if (ops->cmd) {
@@ -751,11 +751,11 @@ int handle_message(struct sock_info *sock_info,
 					goto error;
 				}
 				ret = len;
-				goto end;
+				goto error;
 			} else {
 				DBG("incorrect channel data message size: %zd", len);
 				ret = -EINVAL;
-				goto end;
+				goto error;
 			}
 		}
 		args.channel.chan_data = chan_data;
@@ -776,7 +776,7 @@ int handle_message(struct sock_info *sock_info,
 			&args.stream.shm_fd,
 			&args.stream.wakeup_fd);
 		if (ret) {
-			goto end;
+			goto error;
 		}
 		if (ops->cmd)
 			ret = ops->cmd(lum->handle, lum->cmd,
@@ -796,7 +796,6 @@ int handle_message(struct sock_info *sock_info,
 		break;
 	}
 
-end:
 	lur.handle = lum->handle;
 	lur.cmd = lum->cmd;
 	lur.ret_val = ret;
@@ -1397,7 +1396,13 @@ restart:
 			print_cmd(lum.cmd, lum.handle);
 			ret = handle_message(sock_info, sock, &lum);
 			if (ret) {
-				ERR("Error handling message for %s socket", sock_info->name);
+				ERR("Error handling message for %s socket",
+					sock_info->name);
+				/*
+				 * Close socket if protocol error is
+				 * detected.
+				 */
+				goto end;
 			}
 			continue;
 		default:
-- 
2.34.1