fixup i/o handler return values

Particularly important for lxc_cmd_handler() handles client
input and should not be capable of canceling the main loop,
some syscall return values leaked through overlapping with
LXC_MAINLOOP_ERROR, causing unauthorized clients connecting
to the command socket to shutdown the main loop.

In turn, signal_handler() receiving unexpected
`signalfd_siginfo` struct sizes seems like a reason to bail
(since it's a kernel interface).

Signed-off-by: Wolfgang Bumiller <w.bumiller@proxmox.com>
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

src/lxc/commands.c

@@ -1450,7 +1450,7 @@ static int lxc_cmd_handler(int fd, uint32_t events, void *data,
 		if (errno == EACCES) {
 			/* We don't care for the peer, just send and close. */
 			struct lxc_cmd_rsp rsp = {
-				.ret = ret,
+				.ret = -EPERM,
 			};
 
 			lxc_cmd_rsp_send(fd, &rsp);
@@ -1464,14 +1464,11 @@ static int lxc_cmd_handler(int fd, uint32_t events, void *data,
 
 	if (ret != sizeof(req)) {
 		WARN("Failed to receive full command request. Ignoring request for \"%s\"", lxc_cmd_str(req.cmd));
-		ret = -1;
 		goto out_close;
 	}
 
 	if ((req.datalen > LXC_CMD_DATA_MAX) && (req.cmd != LXC_CMD_CONSOLE_LOG)) {
 		ERROR("Received command data length %d is too large for command \"%s\"", req.datalen, lxc_cmd_str(req.cmd));
-		errno = EFBIG;
-		ret = -EFBIG;
 		goto out_close;
 	}
 
@@ -1480,7 +1477,6 @@ static int lxc_cmd_handler(int fd, uint32_t events, void *data,
 		ret = lxc_recv_nointr(fd, reqdata, req.datalen, 0);
 		if (ret != req.datalen) {
 			WARN("Failed to receive full command request. Ignoring request for \"%s\"", lxc_cmd_str(req.cmd));
-			ret = LXC_MAINLOOP_ERROR;
 			goto out_close;
 		}
 
@@ -1490,12 +1486,11 @@ static int lxc_cmd_handler(int fd, uint32_t events, void *data,
 	ret = lxc_cmd_process(fd, &req, handler, descr);
 	if (ret) {
 		/* This is not an error, but only a request to close fd. */
-		ret = LXC_MAINLOOP_CONTINUE;
 		goto out_close;
 	}
 
 out:
-	return ret;
+	return LXC_MAINLOOP_CONTINUE;
 
 out_close:
 	lxc_cmd_fd_cleanup(fd, handler, descr, req.cmd);

src/lxc/seccomp.c

@@ -1478,10 +1478,8 @@ int seccomp_notify_handler(int fd, uint32_t events, void *data,
 		SYSERROR("Failed to send seccomp notification");
 
 out:
-	return 0;
-#else
-	return -ENOSYS;
 #endif
+	return LXC_MAINLOOP_CONTINUE;
 }
 
 void seccomp_conf_init(struct lxc_conf *conf)

src/lxc/start.c

@@ -335,7 +335,7 @@ static int signal_handler(int fd, uint32_t events, void *data,
 		return log_error(LXC_MAINLOOP_ERROR, "Failed to read signal info from signal file descriptor %d", fd);
 
 	if (ret != sizeof(siginfo))
-		return log_error(-EINVAL, "Unexpected size for struct signalfd_siginfo");
+		return log_error(LXC_MAINLOOP_ERROR, "Unexpected size for struct signalfd_siginfo");
 
 	/* Check whether init is running. */
 	info.si_pid = 0;