More work on Linux installer

1 files changed, 177 insertions, 1 deletions

diff --git a/syslinux.c b/syslinux.c
index ed93f968..c15d03b4 100644
--- a/syslinux.c
+++ b/syslinux.c
@@ -13,10 +13,28 @@
 
 /*
  * syslinux.c - Linux installer program for SYSLINUX
+ *
+ * This program ought to be portable.  I hope so, at least.
+ *
+ * HPA note: this program needs too much privilege.  We should probably
+ * access the filesystem directly like mtools does so we don't have to
+ * mount the disk.  Either that or if Linux gets an fmount() system call
+ * we probably could do the mounting ourselves, and make this program
+ * setuid safe.
  */
 
+#include <paths.h>
 #include <stdio.h>
 #include <mntent.h>
+#include <unistd.h>
+#include <fcntl.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <string.h>
+
+#ifndef _PATH_MOUNT
+#define _PATH_MOUNT "/bin/mount"
+#endif
 
 extern const unsigned char bootsect[];
 extern const unsigned int  bootsect_len;
@@ -24,14 +42,172 @@ extern const unsigned int  bootsect_len;
 extern const unsigned char ldlinux[];
 extern const unsigned int  ldlinux_len;
 
+char *program;			/* Name of program */
 char *device;			/* Device to install to */
 
+enum bs_offsets = {
+  bsJump          = 0x00,
+  bsOemName       = 0x03,
+  bsBytesPerSec   = 0x0b,
+  bsSecPerClust   = 0x0d,
+  bsResSectors    = 0x0e,
+  bsFATs          = 0x10,
+  bsRootDirEnts   = 0x11,
+  bsSectors       = 0x13,
+  bsMedia         = 0x15,
+  bsFATsecs       = 0x16,
+  bsSecPerTrack   = 0x18,
+  bsHeads         = 0x1a,
+  bsHiddenSecs    = 0x1c,
+  bsHugeSectors   = 0x20,
+  bsDriveNumber   = 0x24,
+  bsReserved1     = 0x25,
+  bsBootSignature = 0x26,
+  bsVolumeID      = 0x27,
+  bsVolumeLabel   = 0x2b,
+  bsFileSysType   = 0x36,
+  bsCode          = 0x3e,
+  bsSignature     = 0x1fe
+};
+
+#define bsCopyStart bsBytesPerSec
+#define bsCopyLen   (bsCode-bsBytesPerSec)
+
+/*
+ * Access functions for littleendian numbers, possibly misaligned.
+ */
+static uint16 get_16(unsigned char *p)
+{
+  return (uint16)p[0] + ((uint16)p[1] << 8);
+}
+
+static uint32 get_32(unsigned char *p)
+{
+  return (uint32)p[0] + ((uint32)p[1] << 8) +
+    ((uint32)p[2] << 16) + ((uint32)p[3] << 24);
+}
+
 int main(int argc, char *argv[])
 {
+  static unsigned char sectbuf[512], *dp;
+  int *dev_fd;
+  struct stat st;
+  int nb, left, veryold;
+  unsigned int sectors, clusters;
+
+  program = argv[0];
+
   if ( argc != 2 ) {
-    fprintf(stderr, "Usage: %s device\n", argv[0]);
+    fprintf(stderr, "Usage: %s device\n", program);
+    exit(1);
+  }
+
+  device = argv[1];
+
+  /*
+   * First make sure we can open the device at all, and that we have
+   * read/write permission.
+   */
+  dev_fd = open(device, O_RDWR);
+  if ( dev_fd < 0 || fstat(dev_fd, &st) < 0 ) {
+    perror(device);
+    exit(1);
+  }
+
+  if ( !S_ISBLK(st.st_mode) || !S_ISREG(st.st_mode) ) {
+    fprintf("%s: not a block device or regular file\n", device);
+    exit(1);
+  }
+
+  left = 512;
+  dp = sectbuf;
+  while ( left ) {
+    nb = read(dp, left, dev_fd);
+    if ( nb == -1 && errno == EINTR )
+      continue;
+    if ( nb < 0 ) {
+      perror(device);
+      exit(1);
+    } else if ( nb == 0 ) {
+      fprintf(stderr, "%s: no boot sector\n", device);
+      exit(1);
+    }
+    dp += nb;
+    left -= nb;
+  }
+  close(device);
+  
+  /*
+   * Check to see that what we got was indeed an MS-DOS boot sector/superblock
+   */
+
+  if ( sectbuf[bsBootSignature] == 0x29 ) {
+    /* It's DOS, and it has all the new nice fields */
+
+    veryold = 0;
+
+    sectors = get_16(sectbuf+bsSectors);
+    sectors = sectors ? sectors : get_32(sectbuf+bsHugeSectors);
+    clusters = sectors / sectbuf[bsSecPerClust];
+
+    if ( !memcmp(sectbuf+bsFileSysType, "FAT12   ", 8) ) {
+      if ( clust > 4086 ) {
+	fprintf(stderr, "%s: ERROR: FAT12 but claims more than 4086 clusters\n",
+		device);
+	exit(1);
+      }
+    } else {
+      fprintf(stderr, "%s: filesystem type \"%8.8s\" not supported\n",
+	      sectbuf+bsFileSysType);
+      exit(1);
+    }
+  } else {
+    veryold = 1;
+
+    if ( sectbuf[bsSecPerClust] & (sectbuf[bsSecPerClust] - 1) ||
+	 sectbuf[bsSecPerClust] == 0 ) {
+      fprintf(stderr, "%s: This doesn't look like a FAT filesystem\n",
+	      device);
+    }
+
+    sectors = get_16(sectbuf+bsSectors);
+    sectors = sectors ? sectors : get_32(sectbuf+bsHugeSectors);
+    clusters = sectors / sectbuf[bsSecPerClust];
+    
+    if ( clusters > 4086 ) {
+      fprintf(stderr, "%s: Only FAT12 filesystems supported\n", device);
+      exit(1);
+    }
+  }
+
+  if ( get_16(sectbuf+bsBytesPerSec) != 512 ) {
+    fprintf(stderr, "%s: Sector sizes other than 512 not supported\n",
+	    device);
     exit(1);
   }
+  if ( sectbuf[bsSecPerClust] > 64 ) {
+    fprintf(stderr, "%s: Cluster sizes larger than 32K not supported\n",
+	    device);
+  }
+
+  /*
+   * Now mount the device.  If we are non-root we need to find an fstab
+   * entry for this device which has the user flag set.
+   */
+  if ( geteuid() ) {
+    FILE *fstab;
+    struct mntent *mnt;
 
+    if ( !(fstab = setmntent(MNTTAB, "r")) ) {
+      fprintf("%s: cannot open " MNTTAB "\n", program);
+    }
+    
+    while ( (mnt = getmntent(fstab)) ) {
+      if ( !strcmp(device, mnt->mnt_fsname) ) {
+	if ( !strcmp(mnt->mnt_type, "msdos") ||
+	     !strcmp(mnt->mnt_type, "umsdos") ||
+	     !strcmp(mnt->mnt_type, "vfat") ||
+	     !strcmp(mnt->mnt_type, "uvfat") ||
+	     !strcmp(mnt->mnt_type, "auto")
   return 0;
 }