Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965203AbbEECLm (ORCPT ); Mon, 4 May 2015 22:11:42 -0400 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:51014 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752224AbbEEBV7 (ORCPT ); Mon, 4 May 2015 21:21:59 -0400 Content-Type: text/plain; charset="UTF-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit MIME-Version: 1.0 From: Ben Hutchings To: linux-kernel@vger.kernel.org, stable@vger.kernel.org CC: akpm@linux-foundation.org, "David Disseldorp" , "Jeff Layton" , "Steve French" Date: Tue, 05 May 2015 02:16:39 +0100 Message-ID: X-Mailer: LinuxStableQueue (scripts by bwh) Subject: [PATCH 3.2 147/221] cifs: fix use-after-free bug in find_writable_file In-Reply-To: X-SA-Exim-Connect-IP: 192.168.4.249 X-SA-Exim-Mail-From: ben@decadent.org.uk X-SA-Exim-Scanned: No (on shadbolt.decadent.org.uk); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2385 Lines: 83 3.2.69-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: David Disseldorp commit e1e9bda22d7ddf88515e8fe401887e313922823e upstream. Under intermittent network outages, find_writable_file() is susceptible to the following race condition, which results in a user-after-free in the cifs_writepages code-path: Thread 1 Thread 2 ======== ======== inv_file = NULL refind = 0 spin_lock(&cifs_file_list_lock) // invalidHandle found on openFileList inv_file = open_file // inv_file->count currently 1 cifsFileInfo_get(inv_file) // inv_file->count = 2 spin_unlock(&cifs_file_list_lock); cifs_reopen_file() cifs_close() // fails (rc != 0) ->cifsFileInfo_put() spin_lock(&cifs_file_list_lock) // inv_file->count = 1 spin_unlock(&cifs_file_list_lock) spin_lock(&cifs_file_list_lock); list_move_tail(&inv_file->flist, &cifs_inode->openFileList); spin_unlock(&cifs_file_list_lock); cifsFileInfo_put(inv_file); ->spin_lock(&cifs_file_list_lock) // inv_file->count = 0 list_del(&cifs_file->flist); // cleanup!! kfree(cifs_file); spin_unlock(&cifs_file_list_lock); spin_lock(&cifs_file_list_lock); ++refind; // refind = 1 goto refind_writable; At this point we loop back through with an invalid inv_file pointer and a refind value of 1. On second pass, inv_file is not overwritten on openFileList traversal, and is subsequently dereferenced. Signed-off-by: David Disseldorp Reviewed-by: Jeff Layton Signed-off-by: Steve French Signed-off-by: Ben Hutchings --- fs/cifs/file.c | 1 + 1 file changed, 1 insertion(+) --- a/fs/cifs/file.c +++ b/fs/cifs/file.c @@ -1608,6 +1608,7 @@ refind_writable: cifsFileInfo_put(inv_file); spin_lock(&cifs_file_list_lock); ++refind; + inv_file = NULL; goto refind_writable; } } -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/