🚀 go-pugleaf

Description:
	If a disk label has correct magic numbers but a badly
	corrupted number of partitions, then the checksum routine
	may run wild.

Repeat-By:
	Corrupt a label suitably,

Fix:
	Make the code that looks for the label more defensive.
	This has the effect of not accepting a label that would
	otherwise be correct except for a too-large number of
	partitions.

*** /usr/tahoesrc/sys/sys/ufs_disksubr.c	Sat Jun 11 18:54:43 1988
--- sys/ufs_disksubr.c	Tue Nov 14 16:14:56 1989
***************
*** 157,165 ****
  	    dlp <= (struct disklabel *)(bp->b_un.b_addr+DEV_BSIZE-sizeof(*dlp));
  	    dlp = (struct disklabel *)((char *)dlp + sizeof(long))) {
  		if (dlp->d_magic != DISKMAGIC || dlp->d_magic2 != DISKMAGIC) {
  			if (msg == NULL)
  				msg = "no disk label";
! 		} else if (dkcksum(dlp) != 0)
  			msg = "disk label corrupted";
  		else {
  			*lp = *dlp;
--- 157,166 ----
  	    dlp <= (struct disklabel *)(bp->b_un.b_addr+DEV_BSIZE-sizeof(*dlp));
  	    dlp = (struct disklabel *)((char *)dlp + sizeof(long))) {
  		if (dlp->d_magic != DISKMAGIC || dlp->d_magic2 != DISKMAGIC) {
  			if (msg == NULL)
  				msg = "no disk label";
! 		} else if (dlp->d_npartitions > MAXPARTITIONS ||
! 			   dkcksum(dlp) != 0)
  			msg = "disk label corrupted";
  		else {
  			*lp = *dlp;
***************
*** 166,180 ****
  			msg = NULL;
  			break;
  		}
  	}
- 	if (lp->d_npartitions > MAXPARTITIONS)
- 		lp->d_npartitions = MAXPARTITIONS;
  	bp->b_flags = B_INVAL | B_AGE;
  	brelse(bp);
  	return (msg);
  }
  
  /*
   * Check new disk label for sensibility
   * before setting it.
   */