linux-kernel - Re: [PATCH] CRED: Fix kernel panic upon security_file

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Date:	Mon, 07 Feb 2011 23:55:20 +0000
From:	David Howells <dhowells@...hat.com>
To:	stable@...nel.org
Cc:	dhowells@...hat.com, akpm@...ux-foundation.org,
	linux-security-module@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Subject: Re: [PATCH] CRED: Fix kernel panic upon security_file_alloc() failure.

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

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>
---

 fs/file_table.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/fs/file_table.c b/fs/file_table.c
index c3e89ad..eb36b6b 100644
--- a/fs/file_table.c
+++ b/fs/file_table.c
@@ -125,13 +125,13 @@ struct file *get_empty_filp(void)
 		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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