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>

diff --git a/liblttng-ust-comm/lttng-ust-comm.c b/liblttng-ust-comm/lttng-ust-comm.c
index 631ff42f0862ea027bd980b24dfbd041bc5bba8e..bbc59fc2f986b26bd582212005b0e48c60f3a0ec 100644 (file)
--- 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 e1426139d064984decf8066c6d096e121b556d7c..0a3de32263c068fbffa7c2968218df8dcc14c8a9 100644 (file)
--- a/liblttng-ust/lttng-ust-comm.c
+++ b/liblttng-ust/lttng-ust-comm.c
@@ -576,13 +576,13 @@ 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) {
@@ -643,12 +643,12 @@ 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;
@@ -708,12 +708,12 @@ 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) {
@@ -754,11 +754,11 @@ 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;
@@ -779,7 +779,7 @@ 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,
@@ -799,7 +799,6 @@ int handle_message(struct sock_info *sock_info,
                break;
        }
 
-end:
        lur.handle = lum->handle;
        lur.cmd = lum->cmd;
        lur.ret_val = ret;
@@ -1400,7 +1399,13 @@ 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: