Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753187AbdHVTe5 (ORCPT ); Tue, 22 Aug 2017 15:34:57 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:43400 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752641AbdHVTJz (ORCPT ); Tue, 22 Aug 2017 15:09:55 -0400 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Otto Ebeling , "Eric W. Biederman" , Willy Tarreau , Linus Torvalds Subject: [PATCH 3.18 08/10] Sanitize move_pages() permission checks Date: Tue, 22 Aug 2017 12:09:40 -0700 Message-Id: <20170822190854.470374447@linuxfoundation.org> X-Mailer: git-send-email 2.14.1 In-Reply-To: <20170822190854.104317276@linuxfoundation.org> References: <20170822190854.104317276@linuxfoundation.org> User-Agent: quilt/0.65 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2583 Lines: 75 3.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Linus Torvalds commit 197e7e521384a23b9e585178f3f11c9fa08274b9 upstream. The 'move_paghes()' system call was introduced long long ago with the same permission checks as for sending a signal (except using CAP_SYS_NICE instead of CAP_SYS_KILL for the overriding capability). That turns out to not be a great choice - while the system call really only moves physical page allocations around (and you need other capabilities to do a lot of it), you can check the return value to map out some the virtual address choices and defeat ASLR of a binary that still shares your uid. So change the access checks to the more common 'ptrace_may_access()' model instead. This tightens the access checks for the uid, and also effectively changes the CAP_SYS_NICE check to CAP_SYS_PTRACE, but it's unlikely that anybody really _uses_ this legacy system call any more (we hav ebetter NUMA placement models these days), so I expect nobody to notice. Famous last words. Reported-by: Otto Ebeling Acked-by: Eric W. Biederman Cc: Willy Tarreau Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman --- mm/migrate.c | 13 ++++--------- 1 file changed, 4 insertions(+), 9 deletions(-) --- a/mm/migrate.c +++ b/mm/migrate.c @@ -37,6 +37,7 @@ #include #include #include +#include #include @@ -1468,7 +1469,6 @@ SYSCALL_DEFINE6(move_pages, pid_t, pid, const int __user *, nodes, int __user *, status, int, flags) { - const struct cred *cred = current_cred(), *tcred; struct task_struct *task; struct mm_struct *mm; int err; @@ -1492,14 +1492,9 @@ SYSCALL_DEFINE6(move_pages, pid_t, pid, /* * Check if this process has the right to modify the specified - * process. The right exists if the process has administrative - * capabilities, superuser privileges or the same - * userid as the target process. - */ - tcred = __task_cred(task); - if (!uid_eq(cred->euid, tcred->suid) && !uid_eq(cred->euid, tcred->uid) && - !uid_eq(cred->uid, tcred->suid) && !uid_eq(cred->uid, tcred->uid) && - !capable(CAP_SYS_NICE)) { + * process. Use the regular "ptrace_may_access()" checks. + */ + if (!ptrace_may_access(task, PTRACE_MODE_READ_REALCREDS)) { rcu_read_unlock(); err = -EPERM; goto out;