tqftpserv: Implement path translation

The tftp clients in the modem requests files from either /readwrite or
/readonly/firmware/image, but as the wlanmdsp.mbn file requested is
signed with a vendor specific key these paths needs to be translated.

/readwrite is translated to /tmp/tqftpserv for now and the
/readonly/firmware/image is translated to a search for the requested
file alongside any of the remoteproc firmware files. The result is that
the wlanmdsp.mbn can be stored in linux-firmware alongside it's
device/vendor specific modem firmware.

Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>

Makefile

@@ -7,7 +7,7 @@ prefix ?= /usr/local
 bindir := $(prefix)/bin
 servicedir := $(prefix)/lib/systemd/system
 
-SRCS := tqftpserv.c
+SRCS := tqftpserv.c translate.c
 
 OBJS := $(SRCS:.c=.o)
 

tqftpserv.c

@@ -40,8 +40,7 @@
 #include <unistd.h>
 
 #include "list.h"
-
-#define BASE_DIR "/"
+#include "translate.h"
 
 #define MAX(x, y) ((x) > (y) ? (x) : (y))
 
@@ -212,7 +211,6 @@ static void handle_rrq(const char *buf, size_t len, struct sockaddr_qrtr *sq)
 	size_t rsize = 0;
 	size_t wsize = 0;
 	bool do_oack = false;
-	char path[256];
 	int sock;
 	int ret;
 	int fd;
@@ -275,10 +273,9 @@ static void handle_rrq(const char *buf, size_t len, struct sockaddr_qrtr *sq)
 		return;
 	}
 
-	snprintf(path, sizeof(path), BASE_DIR "/%s", filename);
-	fd = open(path, O_RDONLY);
+	fd = translate_open(filename, O_RDONLY);
 	if (fd < 0) {
-		printf("[TQFTP] unable to open %s (%d), reject\n", path, errno);
+		printf("[TQFTP] unable to open %s (%d), reject\n", filename, errno);
 		tftp_send_error(sock, 1, "file not found");
 		return;
 	}
@@ -317,7 +314,6 @@ static void handle_wrq(const char *buf, size_t len, struct sockaddr_qrtr *sq)
 	struct tftp_client *client;
 	const char *filename;
 	const char *mode;
-	char path[256];
 	int sock;
 	int ret;
 	int fd;
@@ -333,11 +329,10 @@ static void handle_wrq(const char *buf, size_t len, struct sockaddr_qrtr *sq)
 
 	printf("[TQFTP] WRQ: %s (%s)\n", filename, mode);
 
-	snprintf(path, sizeof(path), BASE_DIR "/%s", filename);
-	fd = open(path, O_WRONLY | O_CREAT, 0666);
+	fd = translate_open(filename, O_WRONLY | O_CREAT);
 	if (fd < 0) {
 		/* XXX: error */
-		printf("[TQFTP] unable to open %s (%d), reject\n", path, errno);
+		printf("[TQFTP] unable to open %s (%d), reject\n", filename, errno);
 		return;
 	}
 

translate.c

@@ -0,0 +1,182 @@
+/*
+ * Copyright (c) 2019, Linaro Ltd.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice,
+ * this list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ * this list of conditions and the following disclaimer in the documentation
+ * and/or other materials provided with the distribution.
+ *
+ * 3. Neither the name of the copyright holder nor the names of its contributors
+ * may be used to endorse or promote products derived from this software without
+ * specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <dirent.h>
+#include <err.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <libgen.h>
+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+
+#include "translate.h"
+
+#define READONLY_PATH	"/readonly/firmware/image/"
+#define READWRITE_PATH	"/readwrite/"
+
+#define FIRMWARE_BASE	"/lib/firmware/"
+
+/**
+ * translate_readonly() - open "file" residing with remoteproc firmware
+ * @file:	file requested, stripped of "/readonly/image/" prefix
+ *
+ * It is assumed that the readonly files requested by the client resides under
+ * /lib/firmware in the same place as its associated remoteproc firmware.  This
+ * function scans through all entries under /sys/class/remoteproc and read the
+ * dirname of each "firmware" file in an attempt to find, and open(2), the
+ * requested file.
+ *
+ * As these files are readonly, it's not possible to pass flags to open(2).
+ *
+ * Return: opened fd on success, -1 otherwise
+ */
+static int translate_readonly(const char *file)
+{
+	char firmware_value[PATH_MAX];
+	char firmware_attr[32];
+	char path[PATH_MAX];
+	struct dirent *de;
+	int firmware_fd;
+	DIR *class_dir;
+	int class_fd;
+	ssize_t n;
+	int fd = -1;
+
+	class_fd = open("/sys/class/remoteproc", O_RDONLY | O_DIRECTORY);
+	if (class_fd < 0) {
+		warn("failed to open remoteproc class");
+		return -1;
+	}
+
+	class_dir = fdopendir(class_fd);
+	if (!class_dir) {
+		warn("failed to opendir");
+		goto close_class;
+	}
+
+	while ((de = readdir(class_dir)) != NULL) {
+		if (!strcmp(de->d_name, ".") || !strcmp(de->d_name, ".."))
+			continue;
+
+		if (strlen(de->d_name) + sizeof("/firmware") > sizeof(firmware_attr))
+			continue;
+		strcpy(firmware_attr, de->d_name);
+		strcat(firmware_attr, "/firmware");
+
+		firmware_fd = openat(class_fd, firmware_attr, O_RDONLY);
+		if (firmware_fd < 0)
+			continue;
+
+		n = read(firmware_fd, firmware_value, sizeof(firmware_value));
+		close(firmware_fd);
+		if (n < 0) {
+			continue;
+		}
+
+		if (strlen(FIRMWARE_BASE) + strlen(firmware_value) + 1 +
+		    strlen(file) + 1 > sizeof(path))
+			continue;
+
+		strcpy(path, FIRMWARE_BASE);
+		strcat(path, dirname(firmware_value));
+		strcat(path, "/");
+		strcat(path, file);
+
+		fd = open(path, O_RDONLY);
+		if (fd >= 0)
+			break;
+
+		if (errno != ENOENT)
+			warn("failed to open %s", path);
+	}
+
+	closedir(class_dir);
+
+close_class:
+	close(class_fd);
+
+	return fd;
+}
+
+/**
+ * translate_readwrite() - open "file" from a temporary directory
+ * @file:	relative path of the requested file, with /readwrite/ stripped
+ * @flags:	flags to be passed to open(2)
+ *
+ * Return: opened fd on success, -1 otherwise
+ */
+static int translate_readwrite(const char *file, int flags)
+{
+	int base;
+	int ret;
+	int fd;
+
+	ret = mkdir("/tmp/tqftpserv", 0700);
+	if (ret < 0 && errno != EEXIST) {
+		warn("failed to create /tmp/tqftpserv");
+		return -1;
+	}
+
+	base = open("/tmp/tqftpserv", O_RDONLY | O_DIRECTORY);
+	if (base < 0) {
+		warn("failed top open /tmp/tqftpserv");
+		return -1;
+	}
+
+	fd = openat(base, file, flags, 0600);
+	close(base);
+	if (fd < 0)
+		warn("failed to open %s", file);
+
+	return fd;
+}
+
+/**
+ * translate_open() - open file after translating path
+ *
+
+ * Strips /readonly/firmware/image and search among remoteproc firmware.
+ * Replaces /readwrite with a temporary directory.
+
+ */
+int translate_open(const char *path, int flags)
+{
+	if (!strncmp(path, READONLY_PATH, strlen(READONLY_PATH)))
+		return translate_readonly(path + strlen(READONLY_PATH));
+	else if (!strncmp(path, READWRITE_PATH, strlen(READWRITE_PATH)))
+		return translate_readwrite(path + strlen(READWRITE_PATH), flags);
+
+	fprintf(stderr, "invalid path %s, rejecting\n", path);
+	errno = ENOENT;
+	return -1;
+}

translate.h

@@ -0,0 +1,6 @@
+#ifndef __TRANSLATE_H__
+#define __TRANSLATE_H__
+
+int translate_open(const char *path, int flags);
+
+#endif