linux-kernel - Re: Kernel oops (bug) in fs/buffers.c:create_empty

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Date:	Sun, 6 Jul 2008 13:31:00 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Arjan van de Ven <arjan@...radead.org>
Cc:	linux-kernel@...r.kernel.org, Al Viro <viro@...IV.linux.org.uk>
Subject: Re: Kernel oops (bug) in fs/buffers.c:create_empty_buffers

On Sun, 6 Jul 2008 13:23:02 -0700 Arjan van de Ven <arjan@...radead.org> wrote:

> Hi,
> 
> caught this one on kerneloops.org: 
> http://www.kerneloops.org/searchweek.php?search=create_empty_buffers
> 
> void create_empty_buffers(struct page *page,
>                         unsigned long blocksize, unsigned long b_state)
> {
>         struct buffer_head *bh, *head, *tail;
> 
>         head = alloc_page_buffers(page, blocksize, 1);
>         bh = head;
>         do {
>                 bh->b_state |= b_state;
>                 tail = bh;
>                 bh = bh->b_this_page;
>         } while (bh);
> 
> 
> turns out, alloc_page_buffers() can fail and return NULL (for AIO for
> example)... yet this code blindly dereferences the result, getting a
> predictable NULL pointer fault.
> 
> It's not directly clear what to do about... make this function return
> the failure to the caller?

isofs has a habit of returning impossible block sizes and the

	while ((offset -= size) >= 0) {

consequently loops zero times and alloc_page_buffers() returns null.

Someone was having a look at it - maybe Jan?

I assume that the kernloops.org records link back to the original
report somewhere but I can't find it?

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