refactor: Enhance handling of sync pipes and broken pipes

change the write_sync_fd function to handle broken pipes. When a broken pipe is detected, the file descriptor is closed and conmon continues gracefully instead of exiting. Closes: containers#438 Signed-off-by: Giuseppe Scrivano <[email protected]>
giuseppe · Aug 9, 2023 · 6e48ceb · 6e48ceb
1 parent 75f8ceb
commit 6e48ceb
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Showing 3 changed files with 14 additions and 8 deletions.
diff --git a/src/conmon.c b/src/conmon.c
@@ -208,7 +208,7 @@ int main(int argc, char *argv[])
 
 		if (opt_attach) {
 			ndebug("sending attach message to parent");
-			write_sync_fd(attach_pipe_fd, 0, NULL);
+			write_or_close_sync_fd(&attach_pipe_fd, 0, NULL);
 			ndebug("sent attach message to parent");
 		}
 	}
@@ -380,7 +380,7 @@ int main(int argc, char *argv[])
 				if (opt_exec && container_status > 0) {
 					to_report = -1 * container_status;
 				}
-				write_sync_fd(sync_pipe_fd, to_report, buf);
+				write_or_close_sync_fd(&sync_pipe_fd, to_report, buf);
 			}
 		}
 		nexitf("Failed to create container: exit status %d", get_exit_status(runtime_status));
@@ -407,7 +407,7 @@ int main(int argc, char *argv[])
 	 * Thus, if we are legacy and we are exec, skip this write.
 	 */
 	if ((opt_api_version >= 1 || !opt_exec) && sync_pipe_fd >= 0)
-		write_sync_fd(sync_pipe_fd, container_pid, NULL);
+		write_or_close_sync_fd(&sync_pipe_fd, container_pid, NULL);
 
 #ifdef __linux__
 	setup_oom_handling(container_pid);
@@ -527,7 +527,7 @@ int main(int argc, char *argv[])
 
 	/* Send the command exec exit code back to the parent */
 	if (opt_exec && sync_pipe_fd >= 0)
-		write_sync_fd(sync_pipe_fd, exit_status, exit_message);
+		write_or_close_sync_fd(&sync_pipe_fd, exit_status, exit_message);
 
 	if (attach_symlink_dir_path != NULL && unlink(attach_symlink_dir_path) == -1 && errno != ENOENT)
 		pexit("Failed to remove symlink for attach socket directory");

diff --git a/src/parent_pipe_fd.c b/src/parent_pipe_fd.c
@@ -26,7 +26,8 @@ int get_pipe_fd_from_env(const char *envname)
 	return pipe_fd;
 }
 
-void write_sync_fd(int fd, int res, const char *message)
+// Write a message to the sync pipe, or close the file descriptor if it's a broken pipe.
+void write_or_close_sync_fd(int *fd, int res, const char *message)
 {
 	const char *res_key;
 	if (opt_api_version >= 1)
@@ -38,7 +39,7 @@ void write_sync_fd(int fd, int res, const char *message)
 
 	ssize_t len;
 
-	if (fd == -1)
+	if (*fd == -1)
 		return;
 
 	_cleanup_free_ char *json = NULL;
@@ -50,7 +51,12 @@ void write_sync_fd(int fd, int res, const char *message)
 	}
 
 	len = strlen(json);
-	if (write_all(fd, json, len) != len) {
+	if (write_all(*fd, json, len) != len) {
+		if (errno == EPIPE) {
+			close(*fd);
+			*fd = -1;
+			return;
+		}
 		pexit("Unable to send container stderr message to parent");
 	}
 }

diff --git a/src/parent_pipe_fd.h b/src/parent_pipe_fd.h
@@ -2,7 +2,7 @@
 #define PARENT_PIPE_FD_H
 
 
-void write_sync_fd(int fd, int res, const char *message);
+void write_or_close_sync_fd(int *fd, int res, const char *message);
 int get_pipe_fd_from_env(const char *envname);
 extern int sync_pipe_fd;