From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 53F78C04A95 for ; Tue, 25 Oct 2022 13:45:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231995AbiJYNpq (ORCPT ); Tue, 25 Oct 2022 09:45:46 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48288 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231429AbiJYNpq (ORCPT ); Tue, 25 Oct 2022 09:45:46 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [IPv6:2604:1380:4601:e00::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 207A6183DB3 for ; Tue, 25 Oct 2022 06:45:45 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id CDEA5B81D4C for ; Tue, 25 Oct 2022 13:45:43 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 67939C433C1; Tue, 25 Oct 2022 13:45:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1666705542; bh=S7b8l0tO/WX4aJRDnq7j/BmRts7xtWVdTNO0cj1/nK8=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=LH+wRHMN/j2Ud2/7+U0Zr1hkYfLCl9kclGL5Klt7yxynuUWLZMuJC8y+HV1tDhook tJYF3JdEhrynsZ4tS1aXSZukPOaVyWDC1gvE1fXH0QDuRvqcLRsEgL1DvPwCDudC80 3S96zTQn363t/4h0tt5HsKIk3vFOOJOgn+KoeOPHmuI9k+93/KiCCUH2jRuqFQXUBz +r2yYeHiU0jdZmpDfNiITTuZdihHZi6TllDekiRxGwXibPhVLcw9qmdDJkAogUDAZ4 xwgWU3i3YZf+z1jyRWHkC8YhrwXCFuhxA65TUsMui3NWOWgSEbGp023VsIYYCHIZ3V pKX8lW/8/TNPQ== Date: Tue, 25 Oct 2022 08:45:41 -0500 From: Seth Forshee To: Christian Brauner Cc: Gaosheng Cui , serge@hallyn.com, paul@paul-moore.com, jmorris@namei.org, linux-security-module@vger.kernel.org Subject: Re: [PATCH] security: commoncap: fix potential memleak on error path from vfs_getxattr_alloc Message-ID: References: <20221025104544.2298829-1-cuigaosheng1@huawei.com> <20221025130459.kk42edsz56vsd3ur@wittgenstein> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20221025130459.kk42edsz56vsd3ur@wittgenstein> Precedence: bulk List-ID: On Tue, Oct 25, 2022 at 03:04:59PM +0200, Christian Brauner wrote: > On Tue, Oct 25, 2022 at 06:45:44PM +0800, Gaosheng Cui wrote: > > In cap_inode_getsecurity(), we will use vfs_getxattr_alloc() to > > complete the memory allocation of tmpbuf, if we have completed > > the memory allocation of tmpbuf, but failed to call handler->get(...), > > there will be a memleak in below logic: > > > > |-- ret = (int)vfs_getxattr_alloc(mnt_userns, ...) <-- alloc for tmpbuf > > |-- value = krealloc(*xattr_value, error + 1, flags) <-- alloc memory > > |-- error = handler->get(handler, ...) <-- if error > > |-- *xattr_value = value <-- xattr_value is &tmpbuf <-- memory leak > > > > So we will try to free(tmpbuf) after vfs_getxattr_alloc() fails to fix it. > > Hey Gaosheng, > > > > > Fixes: 71bc356f93a1 ("commoncap: handle idmapped mounts") > > The Fixes: tag is wrong afaict. The control flow isn't changed in any > way by the referenced commit. > > The logic changed the last time with > 82e5d8cc768b ("security: commoncap: fix -Wstringop-overread warning") > but even that commit wouldn't have introduced the bug. It would've been > introduced by 8db6c34f1dbc ("Introduce v3 namespaced file > capabilities"). So update the Fixes: tag with that reference, please. > > Otherwise I think you in principle have a point. Not sure if we have any > filesystem that in practice would fail after permission checks have > already passed with the first call to ->get() but then fail with the > correct size passed in the second ->get() invocation. Sounds super > unlikely but not impossible. Looks like several other callers have the same problem -- evm_is_immutable(), evm_xattr_change(), ima_eventevmsig_init(). And ima_read_xattr() expects the caller to handle it which seems potentially problematic, though currently only current caller does handle it properly. The documention comment for vfs_getxattr_alloc() needs a warning that the caller needs to free memory even if an error is returned, because that is very counterintuitive. It probably should have been named vfs_getxattr_realloc() ... Seth