Distribution: world
Subject: Re: suid for fdformat?
X-Mailer: cppnews $Revision: 1.14 $
Organization: None
Date: Sun, 6 Sep 1992 18:45:53 +0000


In article <1992Sep6.130207.11486@bernina.ethz.ch> almesber@nessie.cs.id.ethz.ch (Werner Almesberger) writes:

> In article <1992Aug30.062444.346@athena.mit.edu> hammond@kwhpc.caseng.com (Kevin W. Hammond) writes:
> > Should fdformat be installed as a suid program so regular users can format
> > floppies, or is it more typically found installed so only root can format
> > floppies?
> 
> It depends. Formatting is inherently more timing-critical than regular
> floppy accesses because some errors can only be detected in the
> verification pass. Therefore, it's considered an operation that needs
> some awareness on the user's part.
Actually, the 765 series of floppy controller chips used in a PC have a
simple formatting command which, coupled with the use of DMA, makes
formatting discs almost totally non time-critical. This is in sharp
contrast to the old Western Digital 177x/179x series chips which were
quite demanding. 
> If you can live with users creating bad media on a loaded system,
> running fdformat suid isn't a problem. However, you should use the
> slightly modified version I've appended to this posting. It assures
> that only floppy devices can be formatted (the ioctls may have some
> random effect on other devices) and only if the user has write access
> to them.
> 
> - Werner
> 
> ---------------------------------- cut here -----------------------------------
> 
> /* fdformat.c  -  Low-level formats a floppy disk. */
> 
> #include <unistd.h>
> #include <stdio.h>
> #include <string.h>
> #include <fcntl.h>
> #include <errno.h>
> #include <sys/stat.h>
> #include <linux/fd.h>
> 
> 
> static int ctrl;
> struct floppy_struct param;
> 
> 
> #define FLOPPY_MAJOR 2
> #define SECTOR_SIZE 512
> #define PERROR(msg) { perror(msg); exit(1); }
> 
> 
> static void format_disk(char *name)
> {
>     struct format_descr descr;
>     int track;
>     char dummy;
> 
>     printf("Formatting ... ");
>     fflush(stdout);
>     if (ioctl(ctrl,FDFMTBEG,NULL) < 0) PERROR("\nioctl(FDFMTBEG)");
>     for (track = 0; track < param.track; track++) {
> 	descr.track = track;
> 	descr.head = 0;
> 	if (ioctl(ctrl,FDFMTTRK,(int) &descr) < 0) PERROR("\nioctl(FDFMTTRK)");
> 	printf("%3d\b\b\b",track);
> 	fflush(stdout);
> 	if (param.head == 2) {
> 	    descr.head = 1;
> 	    if (ioctl(ctrl,FDFMTTRK,(int) &descr) < 0)
> 		PERROR("\nioctl(FDFMTTRK)");
> 	}
>     }
>     if (ioctl(ctrl,FDFMTEND,NULL) < 0) PERROR("\nioctl(FDFMTEND)");
>     printf("done\n");
> }
> 
> 
> static void verify_disk(char *name)
> {
>     unsigned char *data;
>     int fd,cyl_size,cyl,count;
> 
>     cyl_size = param.sect*param.head*512;
>     if ((data = (unsigned char *) malloc(cyl_size)) == NULL) PERROR("malloc");
>     printf("Verifying ... ");
>     fflush(stdout);
>     if ((fd = open(name,O_RDONLY)) < 0) PERROR(name);
>     for (cyl = 0; cyl < param.track; cyl++) {
> 	printf("%3d\b\b\b",cyl);
> 	fflush(stdout);
> 	if (read(fd,data,cyl_size) != cyl_size) PERROR("read");
> 	for (count = 0; count < cyl_size; count++)
> 	    if (data[count] != FD_FILL_BYTE) {
> 		printf("bad data in cyl %d\nContinuing ... ",cyl);
> 		fflush(stdout);
> 		break;
> 	    }
>     }
>     printf("done\n");
>     if (close(fd) < 0) PERROR("close");
> }
> 
> 
> static void usage(char *name)
> {
>     char *this;
> 
>     if (this = strrchr(name,'/')) name = this+1;
>     fprintf(stderr,"usage: %s [ -n ] device\n",name);
>     exit(1);
> }
> 
> 
> main(int argc,char **argv)
> {
>     int verify;
>     char *name;
>     struct stat st;
> 
>     name = argv[0];
>     verify = 1;
>     if (argc > 1 && argv[1][0] == '-') {
> 	if (argv[1][1] != 'n') usage(name);
> 	verify = 0;
> 	argc--;
> 	argv++;
>     }
>     if (argc != 2) usage(name);
>     if (lstat(argv[1],&st) < 0) PERROR(argv[1]);
>     if (!S_ISBLK(st.st_mode) || st.st_rdev >> 8 != FLOPPY_MAJOR) {
> 	fprintf(stderr,"%s: not a floppy device\n",argv[1]);
> 	exit(1);
>     }
>     if (access(argv[1],W_OK) < 0) PERROR(argv[1]);
>     if ((ctrl = open(argv[1],3)) < 0) PERROR(argv[1]);
>     if (ioctl(ctrl,FDGETPRM,(int) &param) < 0) PERROR("ioctl(FDGETPRM)");
>     printf("%sle-sided, %d tracks, %d sec/track. Total capacity %d kB.\n",
>       param.head ? "Doub" : "Sing",param.track,param.sect,param.size >> 1);
>     format_disk(argv[1]);
>     if (verify) verify_disk(argv[1]);
> }
> -- 
>    _________________________________________________________________________
>   / Werner Almesberger, ETH Zuerich, CH      almesber@nessie.cs.id.ethz.ch /
>  / IFW A44  Tel. +41 1 254 7213                 almesberger@rzvax.ethz.ch /
> /_BITNET:_ALMESBER@CZHETH5A__HEPNET/CHADNET:_[20579::]57414::ALMESBERGER_/
> 
> 
--
Jim Segrave (Segrave Software Services)     jes@grendel.demon.co.uk

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