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Date: Wed, 19 Sep 2001 14:36:10 +0400
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To: linux-kernel@vger.kernel.org
From: "Andrew V. Samoilov" <kai@cmail.ru>
Reply-to: "Andrew V. Samoilov" <kai@cmail.ru>
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Subject: mmap successed but SIGBUS generated on access
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Hi!

I have bad CD-R with a some number of unreadable files.

Then user-space program use mmap system it returns ok but any
attempt to access a memory pointed by this system call finishes 
with SIGBUS. So Midnight Commander internal file viewer faults.

This error is 100 % reproduceable at 2.2.19 and 2.4.2 kernels.

Is there any way to detect such problem in user-space without signal handlers ?

Lines from /var/log/messages:

Sep 19 12:20:05 sav kernel: attempt to access beyond end of device
Sep 19 12:20:05 sav kernel: 16:00: rw=0, want=657860, limit=386954
Sep 19 12:20:05 sav kernel: dev 16:00 blksize=2048 blocknr=328929 sector=1315716 size=2048 
count=1

Test program:

#include <stdio.h>
#include <string.h>
#include <fcntl.h>
#include <sys/stat.h>
#include <unistd.h>
#include <sys/mman.h>
#include <errno.h>

int main (int argc, char ** argv) {
    int fd;
    struct stat st;
    void * p;
    while (--argc) {
	argv++;
	if (stat (*argv, &st)) {
	    fprintf (stderr, "stat (%s) -- %s\n", *argv, strerror (errno));
	    continue;
	}
	if ((fd = open (*argv, O_RDONLY)) == -1) {
	    fprintf (stderr, "open (%s) -- %s\n", *argv, strerror (errno));
	    continue;
	}
	fprintf (stderr, "mmap (%d) called...\n", st.st_size);
	if ((p = mmap (0, st.st_size, PROT_READ, MAP_SHARED, fd, 0)) == (void*) -1) {
	    fprintf (stderr, "mmap (%s) -- %s\n", *argv, strerror (errno));
	    close (fd);
	    continue;
	}
	fputs ("mmap done...\n", stderr);
	write (2, p, st.st_size);
	fputs ("munmap called...\n", stderr);
	if (munmap (p, st.st_size) == -1) {
	    fprintf (stderr, "munmap (%s) -- %s\n", *argv, strerror (errno));
	}
	fputs ("munmap done...\n", stderr);
	close (fd);
    }
}

This program output:

mmap (8) called...
mmap done...
Bus error


--
Regards,
Andrew.

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