From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from out2-smtp.messagingengine.com ([66.111.4.26]:53066 "EHLO out2-smtp.messagingengine.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757737AbdADKPT (ORCPT ); Wed, 4 Jan 2017 05:15:19 -0500 Subject: FAILED: patch "[PATCH] fs: exec: apply CLOEXEC before changing dumpable task flags" failed to apply to 4.4-stable tree To: asarai@suse.de, crosbymichael@gmail.com, stable@vger.kernel.org, viro@zeniv.linux.org.uk Cc: From: Date: Wed, 04 Jan 2017 11:15:20 +0100 Message-ID: <1483524920117136@kroah.com> MIME-Version: 1.0 Content-Type: text/plain; charset=ANSI_X3.4-1968 Content-Transfer-Encoding: 8bit Sender: stable-owner@vger.kernel.org List-ID: The patch below does not apply to the 4.4-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to . thanks, greg k-h ------------------ original commit in Linus's tree ------------------ >>From 613cc2b6f272c1a8ad33aefa21cad77af23139f7 Mon Sep 17 00:00:00 2001 From: Aleksa Sarai Date: Wed, 21 Dec 2016 16:26:24 +1100 Subject: [PATCH] fs: exec: apply CLOEXEC before changing dumpable task flags If you have a process that has set itself to be non-dumpable, and it then undergoes exec(2), any CLOEXEC file descriptors it has open are "exposed" during a race window between the dumpable flags of the process being reset for exec(2) and CLOEXEC being applied to the file descriptors. This can be exploited by a process by attempting to access /proc//fd/... during this window, without requiring CAP_SYS_PTRACE. The race in question is after set_dumpable has been (for get_link, though the trace is basically the same for readlink): [vfs] -> proc_pid_link_inode_operations.get_link -> proc_pid_get_link -> proc_fd_access_allowed -> ptrace_may_access(task, PTRACE_MODE_READ_FSCREDS); Which will return 0, during the race window and CLOEXEC file descriptors will still be open during this window because do_close_on_exec has not been called yet. As a result, the ordering of these calls should be reversed to avoid this race window. This is of particular concern to container runtimes, where joining a PID namespace with file descriptors referring to the host filesystem can result in security issues (since PRCTL_SET_DUMPABLE doesn't protect against access of CLOEXEC file descriptors -- file descriptors which may reference filesystem objects the container shouldn't have access to). Cc: dev@opencontainers.org Cc: # v3.2+ Reported-by: Michael Crosby Signed-off-by: Aleksa Sarai Signed-off-by: Al Viro diff --git a/fs/exec.c b/fs/exec.c index 8112eacf10f3..eadbf5069c38 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -19,7 +19,7 @@ * current->executable is only used by the procfs. This allows a dispatch * table to check for several different types of binary formats. We keep * trying until we recognize the file or we run out of supported binary - * formats. + * formats. */ #include @@ -1268,6 +1268,13 @@ int flush_old_exec(struct linux_binprm * bprm) flush_thread(); current->personality &= ~bprm->per_clear; + /* + * We have to apply CLOEXEC before we change whether the process is + * dumpable (in setup_new_exec) to avoid a race with a process in userspace + * trying to access the should-be-closed file descriptors of a process + * undergoing exec(2). + */ + do_close_on_exec(current->files); return 0; out: @@ -1330,7 +1337,6 @@ void setup_new_exec(struct linux_binprm * bprm) group */ current->self_exec_id++; flush_signal_handlers(current, 0); - do_close_on_exec(current->files); } EXPORT_SYMBOL(setup_new_exec);