Re: Oops when using growisofs

Andrew Morton
2008-06-23T06:35:40Z

On Mon, 23 Jun 2008 00:28:20 +0200 Michael Buesch <mb@bu3sch.de> wrote:

> On Monday 23 June 2008 00:05:51 Michael Buesch wrote:
> > > Note: r9 and r3 are both NULL pointers. r3 is the value returned from alloc_page_buffers.
> > > R9 is a copy of that, which gets accessed.
> >
> > Hm, yeah. I looked at that code already, but I can't see how it could return
> > a NULL pointer.
>
> Well, actually, it can return a NULL pointer.
>
> 928 head = NULL;
> 929 offset = PAGE_SIZE;
> 930 while ((offset -= size) >= 0) {
> ...
> 949 }
> 950 return head;
>
> So if size, which is a passed in as parameter, is > PAGE_SIZE it will return NULL.
>
> The size parameter is calculated by doing
> blocksize = 1 << inode->i_blkbits;
> in an earlier function in the callchain.

Yes, that's a more likely scenario. isofs has a history of passing
garbage into the VFS.

> So, well. I dunno what i_blkbits is. There's no docs in struct inode.

It's log2 of the filesystem blocksize. It'd be interesting to work out
what value isofs is setting it to, and why.