From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.linuxfoundation.org ([140.211.169.12]:57690 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727983AbeIHC1O (ORCPT ); Fri, 7 Sep 2018 22:27:14 -0400 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Jann Horn , Christian Brauner , Serge Hallyn , "Eric W. Biederman" Subject: [PATCH 3.18 21/29] userns: move user access out of the mutex Date: Fri, 7 Sep 2018 23:10:42 +0200 Message-Id: <20180907210910.974712079@linuxfoundation.org> In-Reply-To: <20180907210909.523240901@linuxfoundation.org> References: <20180907210909.523240901@linuxfoundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: stable-owner@vger.kernel.org List-ID: 3.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Jann Horn commit 5820f140edef111a9ea2ef414ab2428b8cb805b1 upstream. The old code would hold the userns_state_mutex indefinitely if memdup_user_nul stalled due to e.g. a userfault region. Prevent that by moving the memdup_user_nul in front of the mutex_lock(). Note: This changes the error precedence of invalid buf/count/*ppos vs map already written / capabilities missing. Fixes: 22d917d80e84 ("userns: Rework the user_namespace adding uid/gid...") Cc: stable@vger.kernel.org Signed-off-by: Jann Horn Acked-by: Christian Brauner Acked-by: Serge Hallyn Signed-off-by: Eric W. Biederman Signed-off-by: Greg Kroah-Hartman --- kernel/user_namespace.c | 22 ++++++++++------------ 1 file changed, 10 insertions(+), 12 deletions(-) --- a/kernel/user_namespace.c +++ b/kernel/user_namespace.c @@ -602,7 +602,16 @@ static ssize_t map_write(struct file *fi struct uid_gid_extent *extent = NULL; unsigned long page = 0; char *kbuf, *pos, *next_line; - ssize_t ret = -EINVAL; + ssize_t ret; + + /* Only allow < page size writes at the beginning of the file */ + if ((*ppos != 0) || (count >= PAGE_SIZE)) + return -EINVAL; + + /* Slurp in the user data */ + if (copy_from_user(kbuf, buf, count)) + return -EFAULT; + kbuf[count] = '\0'; /* * The userns_state_mutex serializes all writes to any given map. @@ -643,17 +652,6 @@ static ssize_t map_write(struct file *fi if (!page) goto out; - /* Only allow < page size writes at the beginning of the file */ - ret = -EINVAL; - if ((*ppos != 0) || (count >= PAGE_SIZE)) - goto out; - - /* Slurp in the user data */ - ret = -EFAULT; - if (copy_from_user(kbuf, buf, count)) - goto out; - kbuf[count] = '\0'; - /* Parse the user data */ ret = -EINVAL; pos = kbuf;