Re: [Bug #13112] Oops in drain_array

FUJITA Tomonori
2009-04-28T14:44:51Z

On Tue, 28 Apr 2009 14:43:37 +0200 (CEST)
Bart <mmx-G/jkD+u3s4s@public.gmane.org> wrote:

> > On Mon, 27 Apr 2009 13:36:46 -0700 (PDT)
> > David Rientjes <rientjes-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org> wrote:
> >
> >> On Mon, 27 Apr 2009, Bart wrote:
> >>
> >>> After turning the suggested debuging options I've got tons of these when
> >>> trying to stress the tape device like before:
> >>>
> >>> Apr 27 16:57:30 fs kernel: [ 96.446708] slab error in verify_redzone_free():
> >>> cache `size-128': memory outside object was overwritten
> >>> Apr 27 16:57:30 fs kernel: [ 96.446713] Pid: 0, comm: swapper Not tainted
> >>> 2.6.29.1-64 #2
> >>> Apr 27 16:57:30 fs kernel: [ 96.446715] Call Trace:
> >>> Apr 27 16:57:30 fs kernel: [ 96.446717] <IRQ> [<ffffffff8029adc5>]
> >>> __slab_error+0x1f/0x25
> >>> Apr 27 16:57:30 fs kernel: [ 96.446728] [<ffffffff8029b24b>]
> >>> cache_free_debugcheck+0x108/0x1d6
> >>> Apr 27 16:57:30 fs kernel: [ 96.446731] [<ffffffff8029b473>]
> >>> kfree+0x81/0xc2
> >>> Apr 27 16:57:30 fs kernel: [ 96.446735] [<ffffffff802bd311>]
> >>> bio_free_map_data+0xc/0x1e
> >>
> >> This appears to be kfree(bmd->iovecs) in bio_free_map_data(). It looks
> >> like the memcpy size in bio_set_map_data() overrides the kmalloc size; in
> >> other words, for a redzone error, bio->bi_vcnt > nr_pages in
> >> bio_copy_user_iov().
> >
> > Can you try this?
> >
> > diff --git a/fs/bio.c b/fs/bio.c
> > index 7bbc98f..6a09356 100644
> > --- a/fs/bio.c
> > +++ b/fs/bio.c
> > @@ -817,6 +817,9 @@ struct bio *bio_copy_user_iov(struct request_queue *q,
> > len += iov[i].iov_len;
> > }
> >
> > + if (offset)
> > + nr_pages += 1;
> > +
> > bmd = bio_alloc_map_data(nr_pages, iov_count, gfp_mask);
> > if (!bmd)
> > return ERR_PTR(-ENOMEM);
> >
>
> There are no more errors in the dmesg after applying this patch to
> 2.6.29.2.
>
> Without this patch I can reproduce this kind of errors on
> 2.6.29.1, 2.6.29.2.
>
> I've not tested this patch with 2.6.29.1 and 2.6.30rc3-git3.
> I will try to reproduce the error on 2.6.30rc3-git3 as soon as I compile
> it.

Thanks for testing! And very sorry about the bug.

I'm sure that you hit the same bug with 2.6.30-rc3-git.

Jens, can you please apply this against 2.6.30-rc (and we need this
for 2.6.29.x too)?

I know that bio_copy_user_iov() is hacky. I'll try to clean up the
mapping API later.

=
From: FUJITA Tomonori <fujita.tomonori-Zyj7fXuS5i5L9jVzuh4AOg@public.gmane.org>
Subject: [PATCH] bio: fix memcpy corruption in bio_copy_user_iov()

st driver uses blk_rq_map_user() in order to just build a request out
of page frames. In this case, map_data->offset is a non zero value and
iov[0].iov_base is NULL. We need to increase nr_pages for that.

Cc: stable-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org
Signed-off-by: FUJITA Tomonori <fujita.tomonori-Zyj7fXuS5i5L9jVzuh4AOg@public.gmane.org>
---
fs/bio.c | 3 +++
1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/fs/bio.c b/fs/bio.c
index 7bbc98f..9871164 100644
--- a/fs/bio.c
+++ b/fs/bio.c
@@ -817,6 +817,9 @@ struct bio *bio_copy_user_iov(struct request_queue *q,
len += iov[i].iov_len;
}

+ if (offset)
+ nr_pages++;
+
bmd = bio_alloc_map_data(nr_pages, iov_count, gfp_mask);
if (!bmd)
return ERR_PTR(-ENOMEM);
--
1.6.0.6