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

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Message-ID: <18080.22813.143226.671265@notabene.brown>
Date:	Fri, 20 Jul 2007 16:41:33 +1000
From:	Neil Brown <neilb@...e.de>
To:	"Satyam Sharma" <satyam.sharma@...il.com>
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

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.

> 
> 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;
 }
-
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