linux-kernel - Re: BUG: unable to handle kernel NULL pointer dereference

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Date:	Fri, 20 Jul 2007 12:43:13 +0530
From:	"Satyam Sharma" <satyam.sharma@...il.com>
To:	"Neil Brown" <neilb@...e.de>
Cc:	"David CHANIAL" <david.ml@...o-web.fr>,
	"Linux Kernel Mailinglist" <linux-kernel@...r.kernel.org>
Subject: Re: BUG: unable to handle kernel NULL pointer dereference - nfs v3

Hi,

On 7/20/07, Neil Brown <neilb@...e.de> wrote:
> On Thursday July 19, satyam.sharma@...il.com wrote:
> > Ugh, not a good day for me today ... my earlier conclusion was right,
> > but not the reasoning behind it ... hopefully this time I'll do better :-)
>
>
> Looks good.  Thanks for your helpful analysis.

Thanks, good to know I was of some help :-)

[ For pedantic correctness, of course, s/word/dword/ in the last mail,
considering "word" size is still 16-bit on i386 -- but then that's the
weird backward-compatibility nomenclature/behaviour of i386. ]

> > 0x34 bytes is the offset of ex_uuid in struct fh_export.
> > %ecx == 0, which means ex_uuid was NULL.
>
> Yup. That shouldn't happen, but I can see that it is possible.
>
> There was another case were ex_uuid could conceivably be referenced
> while NULL that I fixed a little while ago.  Looks like I need to fix
> this one too.  Something like the following.
>
> Thanks,
> NeilBrown
>
> Signed-off-by: Neil Brown <neilb@...e.de>
>
> ### Diffstat output
>  ./fs/nfsd/nfsfh.c |   20 +++++++++++++++-----
>  1 file changed, 15 insertions(+), 5 deletions(-)
>
> diff .prev/fs/nfsd/nfsfh.c ./fs/nfsd/nfsfh.c
> --- .prev/fs/nfsd/nfsfh.c       2007-07-13 17:41:48.000000000 +1000
> +++ ./fs/nfsd/nfsfh.c   2007-07-20 12:53:36.000000000 +1000
> @@ -566,13 +566,23 @@ enum fsid_source fsid_source(struct svc_
>         case FSID_DEV:
>         case FSID_ENCODE_DEV:
>         case FSID_MAJOR_MINOR:
> -               return FSIDSOURCE_DEV;
> +               if (fhp->fh_export->ex_dentry->d_inode->i_sb->s_type->fs_flags
> +                   & FS_REQUIRES_DEV)
> +                       return FSIDSOURCE_DEV;
> +               break;
>         case FSID_NUM:
> -               return FSIDSOURCE_FSID;
> -       default:
>                 if (fhp->fh_export->ex_flags & NFSEXP_FSID)
>                         return FSIDSOURCE_FSID;
> -               else
> -                       return FSIDSOURCE_UUID;
> +               break;
> +       default:
> +               break;
>         }
> +       /* either a UUID type filehandle, or the filehandle doesn't
> +        * match the export.
> +        */
> +       if (fhp->fh_export->ex_flags & NFSEXP_FSID)
> +               return FSIDSOURCE_FSID;
> +       if (fhp->fh_export->ex_uuid)
> +               return FSIDSOURCE_UUID;
> +       return FSIDSOURCE_DEV;
>  }
>

David, please try this and let us know if it solves your problems.

Thanks,
Satyam
-
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