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Subjectmmap successed but SIGBUS generated on access
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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