Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932091AbbDQNds (ORCPT ); Fri, 17 Apr 2015 09:33:48 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:33729 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932296AbbDQNdh (ORCPT ); Fri, 17 Apr 2015 09:33:37 -0400 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, David Disseldorp , Jeff Layton , Steve French Subject: [PATCH 3.14 34/43] cifs: fix use-after-free bug in find_writable_file Date: Fri, 17 Apr 2015 15:29:08 +0200 Message-Id: <20150417132557.487984746@linuxfoundation.org> X-Mailer: git-send-email 2.3.5 In-Reply-To: <20150417132556.014766917@linuxfoundation.org> References: <20150417132556.014766917@linuxfoundation.org> User-Agent: quilt/0.64 MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-15 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2403 Lines: 85 3.14-stable 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: Greg Kroah-Hartman --- fs/cifs/file.c | 1 + 1 file changed, 1 insertion(+) --- a/fs/cifs/file.c +++ b/fs/cifs/file.c @@ -1821,6 +1821,7 @@ 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/