From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.linuxfoundation.org ([140.211.169.12]:48944 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728693AbeIHCMQ (ORCPT ); Fri, 7 Sep 2018 22:12:16 -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 4.14 69/89] userns: move user access out of the mutex Date: Fri, 7 Sep 2018 23:10:03 +0200 Message-Id: <20180907210900.557863529@linuxfoundation.org> In-Reply-To: <20180907210852.341064285@linuxfoundation.org> References: <20180907210852.341064285@linuxfoundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: stable-owner@vger.kernel.org List-ID: 4.14-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 | 24 ++++++++++-------------- 1 file changed, 10 insertions(+), 14 deletions(-) --- a/kernel/user_namespace.c +++ b/kernel/user_namespace.c @@ -650,7 +650,16 @@ static ssize_t map_write(struct file *fi unsigned idx; struct uid_gid_extent *extent = NULL; char *kbuf = NULL, *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 */ + kbuf = memdup_user_nul(buf, count); + if (IS_ERR(kbuf)) + return PTR_ERR(kbuf); /* * The userns_state_mutex serializes all writes to any given map. @@ -684,19 +693,6 @@ static ssize_t map_write(struct file *fi if (cap_valid(cap_setid) && !file_ns_capable(file, ns, CAP_SYS_ADMIN)) 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 */ - kbuf = memdup_user_nul(buf, count); - if (IS_ERR(kbuf)) { - ret = PTR_ERR(kbuf); - kbuf = NULL; - goto out; - } - /* Parse the user data */ ret = -EINVAL; pos = kbuf;