Hi,
sf...@users.sourceforge.net írta:
> Hello Laszlo,
>
> Tth_Lszl_Attila:
>> We are using aufs heavily, and during calling chown() from a
program, the aufs code tries to dereference a NULL pointer.
>>
>> The kernel is 2.6.27 in Ubuntu Intrepid, the corresponding aufs code is:
>>
>> Downloaded from:
pserver:anonym...@aufs.cvs.sourceforge.net:/cvsroot/aufs
>> Current Version: Mon, 22 Sep 2008
>> Comments: Unmodified upstream checkout
>
> It is obsoleted.
> Try aufs2 for linux-2.6.27.
We are using aufs over aufs, thus it is not an alternative now.
>
>
>> I checked a newer version which is in Karmic, but I didn't found a
significant difference in the related codes parts.
> :::
>> Unfortunatelly the file->private_data is a NULL pointer, and the
offset of the rw semaphore would be 4 as it appears in the backtrace.
After I examined the code it seemed that this is impossible because if
a file is opened, the related private_data is set to non-null by
au_finfo_init() or if it is still a NULL pointer, the return value of
the function is -ENOMEM. In this case the application-level open()
function fails.
>
> Exactly.
> In aufs, file->private_data should not be NULL.
> I don't know what went wrong, but I'd strongly recommend you to try
> aufs2 and not to use the oboleted aufs1.
>
Later switching to aufs2 may be possible, but we can't yet.
This bug is quite strange, I know, but have you any idea what other can
set the file's private_data member?
My workaround is the following:
* additional condition: the private data must be non-null
* if this condition is not met, the ATTR_FILE is removed from
ia->ia_valid
if (ia->ia_valid & ATTR_FILE && ia->ia_file &&
ia->ia_file->private_data) {
/* currently ftruncate(2) only */
file = ia->ia_file;
fi_write_lock(file);
ia->ia_file = au_h_fptr(file, au_fbstart(file));
} else if (ia->ia_valid & ATTR_FILE) {
ia->ia_valid = ~ATTR_FILE;
}
The NULL dereference problem is gone, but that may break something.
--
Laszlo
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