[linux-lvm] pvcreate: possible problem near line 98 of lib/pv_get_size.c

[Seth D. Alford]

I'm trying to install RedHat 7.1 onto a system which has no existing partitions.
I want one of the filesystems to be an LVM volume.  I modified the RH 7.1
BOOT kernel to include an lvm-mod.o, and I managed to get the LVM binaries
included in the ramdisk itself.  When I try to run pvcreate, though, it
gets a segmentation fault.

The partitions which RedHat is trying to create are in /mnt/sysimage.
Part of my installation process runs chrooted in /mnt/sysimage.

The segfault is happening, I think, near line 98 of lib/pv_get_size.c.  I
isolated it there by running pvcreate with the debug flag, both chrooted to
/mnt/sysimage and not chrooted to /mnt/sysimage, while in ramdisk.  There's a
for loop just before line 98.  The for loop looks at an st_rdev (which I think
is a system call parameter) and tries to match it with a record in an array of
records.  At line 98, the code references the matching array element.  I'm
guessing, but in the non-chrooted environment, the for loop doesn't match any
of the members of the array.  The index variable, i, is one greater than the
size of the array.  The code proceeds to dereference with that value, anyway,
and causes the segmentation fault.

Here's the fragment from pv_get_size.c where I think the problem happens:

         for ( i = 0; i < dir_cache_count; i++) {
            if ( dir_cache[i].st_rdev == st_rdev)
               break;
         }
	
	 /* The above loop assumes that it exits with the break.
	 If it doesn't exit with the break, then i is one more
	 than the size of the array, which will cause a segmentation
	 fault. */
         strncpy ( disk_dev_name, dir_cache[i].dev_name,
                   sizeof ( disk_dev_name) - 1);

This is in 0.9.1_beta6 of LVM.  I would send you a core file, but
the ramdisk environment doesn't allow for creation of core files.

--Seth