dosfs: detect 0xE9 (JMP rel16) in BPB

src/corrupt.c

@@ -43,13 +43,15 @@ match_rule(config_t *conf, dosfile_t *file)
 int
 corrupt_file(dosfs_t *fsd, dosfile_t *file, config_t *conf, uint32_t *state)
 {
-    uint32_t off;
+    uint32_t off, end;
     int real_off;
     unsigned char c;
     struct conf_opts_t opts;
 
+    end = (conf->end) ? conf->end : file->ent.size;
+
     opts = conf->opts;
-    for (off = conf->start; (off < conf->end) && (off < file->ent.size);
+    for (off = conf->start; (off < end) && (off < file->ent.size);
         off += xs_randb(state, conf->skip_a, conf->skip_b)) {
         real_off = get_byte_offset(fsd, file, off);
         if (real_off < 0) {

src/dosfs.c

@@ -34,7 +34,8 @@ open_image(const char *path, int flags, dosfs_t *fsd)
         return errno;
     }
 
-    if (fsd->ib.jmp[0] != 0xEB || fsd->ib.jmp[2] != 0x90) {
+    if ((fsd->ib.jmp[0] != 0xEB || fsd->ib.jmp[2] != 0x90) && /* JMP rel8 */
+        fsd->ib.jmp[0] != 0xE9) { /* JMP rel16 */
         DPRINTF(("hm... doesn't look like a FAT image?\n"));
         close(ifd);
         return EOPNOTSUPP;

src/main.c

@@ -1,26 +1,59 @@
+#include <errno.h>
 #include <fcntl.h>
 #include <stdio.h>
 #include <stdlib.h>
+#include <string.h>
+#include <time.h>
 #include <unistd.h>
 
+#include "config.h"
+#include "corrupt.h"
 #include "dosfs.h"
 
 static void usage(void) __dead;
 static int  list_img(char *);
+static int  do_corrupt(char *, config_t *, uint32_t);
 
 int
 main(int argc, char *argv[])
 {
-    int ch, list_mode;
+    int ch, list_mode, res, preseed;
+    uint32_t seed;
+    char *cfg_path, *ep;
+    config_t *conf;
 
     setprogname(argv[0]);
 
     list_mode = 0;
-    while ((ch = getopt(argc, argv, "l")) != -1) {
+    seed = 0;
+    preseed = 0;
+    cfg_path = NULL;
+    while ((ch = getopt(argc, argv, "lc:s:")) != -1) {
         switch (ch) {
         case 'l':
             list_mode = 1;
             break;
+        case 'c':
+            cfg_path = optarg;
+            break;
+        case 's':
+            errno = 0;
+            if (optarg[0] == '0' && optarg[1] == 'x') {
+                // strtoul hex
+                optarg += 2;
+                seed = strtoul(optarg, &ep, 16);
+            } else {
+                seed = strtoul(optarg, &ep, 10);
+            }
+            if (errno) {
+                perror("couldn't parse seed parameter");
+                return EXIT_FAILURE;
+            } else if (optarg == ep || *ep != 0) {
+                fprintf(stderr, "defined seed is malformed\n");
+                return EXIT_FAILURE;
+            }
+            preseed = 1;
+            break;
         case '?':
         default:
             usage();
@@ -39,10 +72,28 @@ main(int argc, char *argv[])
         return list_img(argv[0]);
     }
 
-    /* TODO: rest of the owl */
-    fprintf(stderr, "not yet implemented :(\n");
+    if (!preseed) {
+        seed = time(NULL) & 0xffffffff;
+    }
 
-    return EXIT_FAILURE;
+    printf("using seed 0x%x\n", seed);
+
+    if (cfg_path != NULL) {
+        conf = parse_config(cfg_path);
+        if (conf == NULL) {
+            fprintf(stderr, "failed to parse config\n");
+            return EXIT_FAILURE;
+        }
+    } else {
+        fprintf(stderr, "no default config implemented\n");
+        return EXIT_FAILURE;
+    }
+
+    res = do_corrupt(argv[0], conf, seed);
+
+    free_config(conf);
+
+    return res;
 }
 
 static int
@@ -54,7 +105,7 @@ list_img(char *path)
 
     res = open_image(path, O_RDONLY, &img);
     if (res != 0) {
-        fprintf(stderr, "err: couldn't open image (errno %d)\n", res);
+        fprintf(stderr, "err: couldn't open image: %s\n", strerror(res));
         return EXIT_FAILURE;
     }
 
@@ -77,10 +128,48 @@ list_img(char *path)
     return EXIT_SUCCESS;
 }
 
+static int
+do_corrupt(char *path, config_t *conf, uint32_t seed)
+{
+    dosfs_t img = { 0 };
+    dosfile_t *rootdir, *cur;
+    config_t *match;
+    int res;
+
+    res = open_image(path, O_RDWR, &img);
+    if (res != 0) {
+        fprintf(stderr, "err: couldn't open image: %s\n", strerror(res));
+        return EXIT_FAILURE;
+    }
+
+    rootdir = dos_listdir(&img, img.root_loc);
+    if (rootdir == NULL) {
+        perror("couldn't read root dir");
+        close_image(&img);
+        return EXIT_FAILURE;
+    }
+
+    for (cur = rootdir; cur->next != NULL; cur = cur->next) {
+        match = match_rule(conf, cur);
+        if (match != NULL) {
+            printf("Corrupting %s.%s... (x%u a%u l%u r%u)\n",
+                cur->fname, cur->fext, match->opts.bit_xor,
+                match->opts.add, match->opts.shl, match->opts.shr);
+            res = corrupt_file(&img, cur, match, &seed);
+            if (res != 0) {
+                fprintf(stderr, "Corrupting file failed...\n");
+            }
+        }
+    }
+
+    close_image(&img);
+    return 0;
+}
+
 static void
 usage(void)
 {
-    fprintf(stderr, "usage: %s [-l] image\n", getprogname());
+    fprintf(stderr, "usage: %s [-l] [-s seed] [-c config] image\n", getprogname());
     exit(EXIT_FAILURE);
 }