From 78d6a052fc6431ad45ff3a24461fd7744a3c1c28 Mon Sep 17 00:00:00 2001
From: Jakob Kaivo <jkk@ung.org>
Date: Tue, 17 Nov 2020 20:32:26 -0500
Subject: enforce device type of mmcblk, fail if /sys/block/<device>/device is
 not a readable directory

---
 deonebook.c | 12 +++++++++++-
 deonebook.h |  2 +-
 genkey.c    | 26 ++++++++++++++------------
 3 files changed, 26 insertions(+), 14 deletions(-)

diff --git a/deonebook.c b/deonebook.c
index 23b61ea..f943396 100644
--- a/deonebook.c
+++ b/deonebook.c
@@ -1,4 +1,5 @@
 #define _XOPEN_SOURCE 700
+#include <dirent.h>
 #include <string.h>
 #include <stdio.h>
 #include <unistd.h>
@@ -37,12 +38,21 @@ int main(int argc, char *argv[])
 			if (optind < argc) {
 				device = argv[optind];
 			}
+
 			if (strstr(device, "mmcblk") != device) {
 				fprintf(stderr, "device must be an mmcblk device\n");
 				return 1;
 			}
 
-			key = genkey(device);
+			char path[256];
+			snprintf(path, sizeof(path), "/sys/block/%s/device", device);
+			DIR *d = opendir(path);
+			if (d == NULL) {
+				fprintf(stderr, "device '%s' not found\n", device);
+				return 1;
+			}
+
+			key = genkey(dirfd(d));
 		}
 
 		if (key == NULL) {
diff --git a/deonebook.h b/deonebook.h
index 23ef2f7..6daf22a 100644
--- a/deonebook.h
+++ b/deonebook.h
@@ -3,7 +3,7 @@
 
 #define KEY_SIZE 16
 
-unsigned char *genkey(const char *dev);
+unsigned char *genkey(int dirfd);
 unsigned char *readkey(const char *path);
 
 #endif
diff --git a/genkey.c b/genkey.c
index 8bb224a..fd17060 100644
--- a/genkey.c
+++ b/genkey.c
@@ -1,8 +1,12 @@
+#define _XOPEN_SOURCE 700
 #include <ctype.h>
+#include <fcntl.h>
 #include <stdio.h>
 #include <string.h>
 #include <stdbool.h>
 #include <stdlib.h>
+#include <unistd.h>
+
 #include "deonebook.h"
 
 #define SCR_SIZE 8
@@ -34,27 +38,25 @@ static unsigned char twiddle(unsigned char buf[2])
 	return c;
 }
 
-static bool get_sd_register(const char *dev, const char *reg, size_t n, unsigned char buf[n])
+static bool get_sd_register(int dirfd, const char *reg, size_t n, unsigned char buf[n])
 {
-	char path[256];
-	snprintf(path, sizeof(path), "/sys/block/%s/device/%s", dev, reg);
-
-	FILE *f = fopen(path, "r");
-	if (f == NULL) {
+	int fd = openat(dirfd, reg, O_RDONLY);
+	if (fd == -1) {
 		return false;
 	}
 
 	for (size_t i = 0; i < n; i++) {
 		unsigned char hex[2];
-		fread(hex, 2, 1, f);
+		read(fd, hex, sizeof(hex));
 		buf[i] = twiddle(hex);
 	}
 
-	fclose(f);
+	close(fd);
+
 	return true;
 }
 
-unsigned char * genkey(const char *dev)
+unsigned char * genkey(int dirfd)
 {
 	static unsigned char key[KEY_SIZE];
 	const unsigned char keycode[] = "eone";
@@ -65,15 +67,15 @@ unsigned char * genkey(const char *dev)
 	unsigned char csd[CSD_SIZE] = "testtesttesttest";
 	unsigned char cid[CID_SIZE] = "testtesttesttest";
 
-	if (!get_sd_register(dev, "cid", sizeof(cid), cid)) {
+	if (!get_sd_register(dirfd, "cid", sizeof(cid), cid)) {
 		fprintf(stderr, "warning: CID register not read\n");
 		allread = false;
 	}
-	if (!get_sd_register(dev, "csd", sizeof(csd), csd)) {
+	if (!get_sd_register(dirfd, "csd", sizeof(csd), csd)) {
 		fprintf(stderr, "warning: CSD register not read\n");
 		allread = false;
 	}
-	if (!get_sd_register(dev, "scr", sizeof(scr), scr)) {
+	if (!get_sd_register(dirfd, "scr", sizeof(scr), scr)) {
 		fprintf(stderr, "warning: SCR register not read\n");
 		allread = false;
 	}
-- 
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