linux-kernel - Re: Oops in audit_copy

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Message-ID: <1343837499.18359.7.camel@tucsk.pomaz.szeredi.hu>
Date:	Wed, 01 Aug 2012 18:11:39 +0200
From:	Miklos Szeredi <mszeredi@...e.cz>
To:	Peter Moody <pmoody@...gle.com>
Cc:	linux-kernel@...r.kernel.org, Kees Cook <keescook@...gle.com>,
	viro@...iv.linux.org.uk, Eric Paris <eparis@...hat.com>,
	miklos@...redi.hu
Subject: Re: Oops in audit_copy_inode

Hi Peter,

Thanks for the report.

Here's a patch.  I haven't tested it but I'm pretty confident that it
fixes the bug.

Thanks,
Miklos


Subject: vfs: fix audit_inode on negative dentry
From: Miklos Szeredi <mszeredi@...e.cz>

Peter Moody reported an oops in audit_copy_inode() and bisected it to commit
7157486541 (vfs: do_last(): common slow lookup).

The problem is that audit_inode() in do_last() is called with a negative dentry.

Previously the non-O_CREAT case didn't call audit_inode() here, but now both
O_CREAT and non-O_CREAT opens are handled by the same code.

I really have no idea why this audit_inode() is needed here at all but am afaid
to remove this for fear of breaking audit somehow.  So just fix this case by
checking for a negative dentry.

Reported-by: Peter Moody <pmoody@...gle.com>
Signed-off-by: Miklos Szeredi <mszeredi@...e.cz>
CC: stable@...r.kernel.org
---
 fs/namei.c |   10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

Index: linux-2.6/fs/namei.c
===================================================================
--- linux-2.6.orig/fs/namei.c	2012-08-01 17:47:28.000000000 +0200
+++ linux-2.6/fs/namei.c	2012-08-01 17:49:26.000000000 +0200
@@ -2607,10 +2607,12 @@ static int do_last(struct nameidata *nd,
 		goto finish_open_created;
 	}
 
-	/*
-	 * It already exists.
-	 */
-	audit_inode(pathname, path->dentry);
+	if (path->dentry->d_inode) {
+		/*
+		 * It already exists.
+		 */
+		audit_inode(pathname, path->dentry);
+	}
 
 	/*
 	 * If atomic_open() acquired write access it is dropped now due to


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