linux-kernel - [PATCH] [119/275] CRED: Fix kernel panic upon security_file

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Date:	Wed, 30 Mar 2011 14:05:58 -0700 (PDT)
From:	Andi Kleen <andi@...stfloor.org>
To:	penguin-kernel@...ove.sakura.ne.jp,
	penguin-kernel@...ove.SAKURA.ne.jp, dhowells@...hat.com,
	torvalds@...ux-foundation.org, gregkh@...e.de, ak@...ux.intel.com,
	linux-kernel@...r.kernel.org, stable@...nel.org,
	tim.bird@...sony.com
Subject: [PATCH] [119/275] CRED: Fix kernel panic upon security_file_alloc() failure.

2.6.35-longterm review patch.  If anyone has any objections, please let me know.

------------------
From: Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>

commit 78d2978874e4e10e97dfd4fd79db45bdc0748550 upstream.

In get_empty_filp() since 2.6.29, file_free(f) is called with f->f_cred == NULL
when security_file_alloc() returned an error.  As a result, kernel will panic()
due to put_cred(NULL) call within RCU callback.

Fix this bug by assigning f->f_cred before calling security_file_alloc().

Signed-off-by: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Signed-off-by: David Howells <dhowells@...hat.com>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>
Signed-off-by: Andi Kleen <ak@...ux.intel.com>

---
 fs/file_table.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Index: linux-2.6.35.y/fs/file_table.c
===================================================================
--- linux-2.6.35.y.orig/fs/file_table.c	2011-03-29 22:51:20.759191992 -0700
+++ linux-2.6.35.y/fs/file_table.c	2011-03-29 23:03:00.692282457 -0700
@@ -123,13 +123,13 @@
 		goto fail;
 
 	percpu_counter_inc(&nr_files);
+	f->f_cred = get_cred(cred);
 	if (security_file_alloc(f))
 		goto fail_sec;
 
 	INIT_LIST_HEAD(&f->f_u.fu_list);
 	atomic_long_set(&f->f_count, 1);
 	rwlock_init(&f->f_owner.lock);
-	f->f_cred = get_cred(cred);
 	spin_lock_init(&f->f_lock);
 	eventpoll_init_file(f);
 	/* f->f_version: 0 */
--
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