From patchwork Mon Jul 1 10:00:35 2013 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Luis Henriques X-Patchwork-Id: 256049 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Received: from huckleberry.canonical.com (huckleberry.canonical.com [91.189.94.19]) by ozlabs.org (Postfix) with ESMTP id D9F4C2C00A3 for ; Mon, 1 Jul 2013 20:00:56 +1000 (EST) Received: from localhost ([127.0.0.1] helo=huckleberry.canonical.com) by huckleberry.canonical.com with esmtp (Exim 4.76) (envelope-from ) id 1Utauf-0007yK-QV; Mon, 01 Jul 2013 10:00:49 +0000 Received: from youngberry.canonical.com ([91.189.89.112]) by huckleberry.canonical.com with esmtp (Exim 4.76) (envelope-from ) id 1UtauS-0007vP-LJ for kernel-team@lists.ubuntu.com; Mon, 01 Jul 2013 10:00:36 +0000 Received: from bl20-124-73.dsl.telepac.pt ([2.81.124.73] helo=localhost) by youngberry.canonical.com with esmtpsa (TLS1.0:DHE_RSA_AES_128_CBC_SHA1:16) (Exim 4.71) (envelope-from ) id 1UtauS-0000UA-BS; Mon, 01 Jul 2013 10:00:36 +0000 From: Luis Henriques To: Artem Bityutskiy Subject: [ 3.5.y.z extended stable ] Patch "UBIFS: fix a horrid bug" has been added to staging queue Date: Mon, 1 Jul 2013 11:00:35 +0100 Message-Id: <1372672835-15133-1-git-send-email-luis.henriques@canonical.com> X-Mailer: git-send-email 1.8.1.2 X-Extended-Stable: 3.5 Cc: kernel-team@lists.ubuntu.com, Al Viro X-BeenThere: kernel-team@lists.ubuntu.com X-Mailman-Version: 2.1.14 Precedence: list List-Id: Kernel team discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , MIME-Version: 1.0 Errors-To: kernel-team-bounces@lists.ubuntu.com Sender: kernel-team-bounces@lists.ubuntu.com This is a note to let you know that I have just added a patch titled UBIFS: fix a horrid bug to the linux-3.5.y-queue branch of the 3.5.y.z extended stable tree which can be found at: http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.5.y-queue If you, or anyone else, feels it should not be added to this tree, please reply to this email. For more information about the 3.5.y.z tree, see https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable Thanks. -Luis ------ From 0edf13f8f1a41c831468b8b2f7035528dd5ec43f Mon Sep 17 00:00:00 2001 From: Artem Bityutskiy Date: Fri, 28 Jun 2013 14:15:15 +0300 Subject: [PATCH] UBIFS: fix a horrid bug commit 605c912bb843c024b1ed173dc427cd5c08e5d54d upstream. Al Viro pointed me to the fact that '->readdir()' and '->llseek()' have no mutual exclusion, which means the 'ubifs_dir_llseek()' can be run while we are in the middle of 'ubifs_readdir()'. This means that 'file->private_data' can be freed while 'ubifs_readdir()' uses it, and this is a very bad bug: not only 'ubifs_readdir()' can return garbage, but this may corrupt memory and lead to all kinds of problems like crashes an security holes. This patch fixes the problem by using the 'file->f_version' field, which '->llseek()' always unconditionally sets to zero. We set it to 1 in 'ubifs_readdir()' and whenever we detect that it became 0, we know there was a seek and it is time to clear the state saved in 'file->private_data'. I tested this patch by writing a user-space program which runds readdir and seek in parallell. I could easily crash the kernel without these patches, but could not crash it with these patches. Reported-by: Al Viro Tested-by: Artem Bityutskiy Signed-off-by: Artem Bityutskiy Signed-off-by: Al Viro [ luis: backported to 3.5: adjusted context ] Signed-off-by: Luis Henriques --- fs/ubifs/dir.c | 30 +++++++++++++++++++++++++++--- 1 file changed, 27 insertions(+), 3 deletions(-) -- 1.8.1.2 diff --git a/fs/ubifs/dir.c b/fs/ubifs/dir.c index 918ce52..1ce4953 100644 --- a/fs/ubifs/dir.c +++ b/fs/ubifs/dir.c @@ -365,6 +365,24 @@ static int ubifs_readdir(struct file *file, void *dirent, filldir_t filldir) */ return 0; + if (file->f_version == 0) { + /* + * The file was seek'ed, which means that @file->private_data + * is now invalid. This may also be just the first + * 'ubifs_readdir()' invocation, in which case + * @file->private_data is NULL, and the below code is + * basically a no-op. + */ + kfree(file->private_data); + file->private_data = NULL; + } + + /* + * 'generic_file_llseek()' unconditionally sets @file->f_version to + * zero, and we use this for detecting whether the file was seek'ed. + */ + file->f_version = 1; + /* File positions 0 and 1 correspond to "." and ".." */ if (pos == 0) { ubifs_assert(!file->private_data); @@ -438,6 +456,14 @@ static int ubifs_readdir(struct file *file, void *dirent, filldir_t filldir) file->f_pos = pos = key_hash_flash(c, &dent->key); file->private_data = dent; cond_resched(); + + if (file->f_version == 0) + /* + * The file was seek'ed meanwhile, lets return and start + * reading direntries from the new position on the next + * invocation. + */ + return 0; } out: @@ -448,15 +474,13 @@ out: kfree(file->private_data); file->private_data = NULL; + /* 2 is a special value indicating that there are no more direntries */ file->f_pos = 2; return 0; } -/* If a directory is seeked, we have to free saved readdir() state */ static loff_t ubifs_dir_llseek(struct file *file, loff_t offset, int origin) { - kfree(file->private_data); - file->private_data = NULL; return generic_file_llseek(file, offset, origin); }