NetNews Usenet Archive 1992 #20/NN_1992_20.iso/spool/comp/os/linux/9993

Text File | 1992-09-08 | 4.9 KB | 167 lines

Path: sparky!uunet!dtix!mimsy!afterlife!jepstei
From: [e-mail] (John Epstein)
Newsgroups: comp.os.linux
Subject: Re: suid for fdformat?
Message-ID: <[e-mail]>
Date: 6 Sep 92 13:36:04 GMT
References: <[e-mail]> <[e-mail]>
Organization: The Great Beyond
Lines: 156

In article <[e-mail]> [e-mail] (Werner Almesberger) writes:
>In article <[e-mail]> [e-mail] (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.
>
>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) ¶m) < 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      [e-mail] /
> / IFW A44  Tel. [phone]                 [e-mail] /
>/_BITNET:_ALMESBER@CZHETH5A__HEPNET/CHADNET:_[20579::]57414::ALMESBERGER_/

Newsgroups: comp.os.linux
Subject: fdformat loops
Distribution: world
Organization: The Great Beyond
Running mcc-interim 0.97p2 software, fdformat looped on:

setfdprm /dev/fd0 1200/1200
fdformat /dev/fd0
looped on "floppy 0: data CRC error: track 77, head 1, sector 1"

CTRL-C was no help, pulled bad disk out of drive --- got 6 errors
reading non-existent disk

This was a little hard on the floppy drive.

Have not yet read the source to fix the problem.

John