From patchwork Sun Sep 18 15:05:15 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Jann Horn X-Patchwork-Id: 9337925 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id 14386601C2 for ; Sun, 18 Sep 2016 15:05:55 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 05F8A28CEB for ; Sun, 18 Sep 2016 15:05:55 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id EF07B28CEE; Sun, 18 Sep 2016 15:05:54 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.9 required=2.0 tests=BAYES_00,RCVD_IN_DNSWL_HI autolearn=ham version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 71B5428CEB for ; Sun, 18 Sep 2016 15:05:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S936317AbcIRPFv (ORCPT ); Sun, 18 Sep 2016 11:05:51 -0400 Received: from thejh.net ([37.221.195.125]:46349 "EHLO thejh.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932871AbcIRPFh (ORCPT ); Sun, 18 Sep 2016 11:05:37 -0400 Received: from pc.thejh.net (pc.vpn [192.168.44.2]) by thejh.net (Postfix) with ESMTPSA id EC6F71826B8; Sun, 18 Sep 2016 17:05:34 +0200 (CEST) From: Jann Horn To: Alexander Viro , Roland McGrath , Oleg Nesterov , John Johansen , James Morris , "Serge E. Hallyn" , Paul Moore , Stephen Smalley , Eric Paris , Casey Schaufler , Kees Cook , Andrew Morton , Janis Danisevskis , Seth Forshee , "Eric . Biederman" , Thomas Gleixner , Benjamin LaHaise Cc: linux-fsdevel@vger.kernel.org, linux-security-module@vger.kernel.org, security@kernel.org Subject: [PATCH 7/9] ptrace: forbid ptrace checks against current_cred() from VFS context Date: Sun, 18 Sep 2016 17:05:15 +0200 Message-Id: <1474211117-16674-8-git-send-email-jann@thejh.net> X-Mailer: git-send-email 2.1.4 In-Reply-To: <1474211117-16674-1-git-send-email-jann@thejh.net> References: <1474211117-16674-1-git-send-email-jann@thejh.net> Sender: owner-linux-security-module@vger.kernel.org Precedence: bulk List-ID: X-Virus-Scanned: ClamAV using ClamSMTP This ensures that VFS implementations don't call ptrace_may_access() from VFS read or write handlers. In order for file descriptor passing to have its intended security properties, VFS read/write handlers must not do any kind of privilege checking. Signed-off-by: Jann Horn --- fs/aio.c | 2 ++ fs/read_write.c | 12 ++++++++++++ fs/splice.c | 12 ++++++++++-- include/linux/sched.h | 4 ++++ kernel/ptrace.c | 7 +++++++ 5 files changed, 35 insertions(+), 2 deletions(-) diff --git a/fs/aio.c b/fs/aio.c index fb8e45b..c941885 100644 --- a/fs/aio.c +++ b/fs/aio.c @@ -1454,9 +1454,11 @@ rw_common: if (rw == WRITE) file_start_write(file); + current->in_unprivileged_vfs++; ret = iter_op(req, &iter); + current->in_unprivileged_vfs--; if (rw == WRITE) file_end_write(file); kfree(iovec); diff --git a/fs/read_write.c b/fs/read_write.c index 66215a7..deddb93 100644 --- a/fs/read_write.c +++ b/fs/read_write.c @@ -472,7 +472,9 @@ ssize_t vfs_read(struct file *file, char __user *buf, size_t count, loff_t *pos) if (!ret) { if (count > MAX_RW_COUNT) count = MAX_RW_COUNT; + current->in_unprivileged_vfs++; ret = __vfs_read(file, buf, count, pos); + current->in_unprivileged_vfs--; if (ret > 0) { fsnotify_access(file); add_rchar(current, ret); @@ -557,7 +559,9 @@ ssize_t vfs_write(struct file *file, const char __user *buf, size_t count, loff_ if (count > MAX_RW_COUNT) count = MAX_RW_COUNT; file_start_write(file); + current->in_unprivileged_vfs++; ret = __vfs_write(file, buf, count, pos); + current->in_unprivileged_vfs--; if (ret > 0) { fsnotify_modify(file); add_wchar(current, ret); @@ -838,12 +842,14 @@ static ssize_t do_readv_writev(int type, struct file *file, iter_fn = file->f_op->write_iter; file_start_write(file); } + current->in_unprivileged_vfs++; if (iter_fn) ret = do_iter_readv_writev(file, &iter, pos, iter_fn, flags); else ret = do_loop_readv_writev(file, &iter, pos, fn, flags); + current->in_unprivileged_vfs--; if (type != READ) file_end_write(file); @@ -1063,12 +1069,14 @@ static ssize_t compat_do_readv_writev(int type, struct file *file, iter_fn = file->f_op->write_iter; file_start_write(file); } + current->in_unprivileged_vfs++; if (iter_fn) ret = do_iter_readv_writev(file, &iter, pos, iter_fn, flags); else ret = do_loop_readv_writev(file, &iter, pos, fn, flags); + current->in_unprivileged_vfs--; if (type != READ) file_end_write(file); @@ -1369,7 +1377,9 @@ static ssize_t do_sendfile(int out_fd, int in_fd, loff_t *ppos, fl = SPLICE_F_NONBLOCK; #endif file_start_write(out.file); + current->in_unprivileged_vfs++; retval = do_splice_direct(in.file, &pos, out.file, &out_pos, count, fl); + current->in_unprivileged_vfs--; file_end_write(out.file); if (retval > 0) { @@ -1512,6 +1522,7 @@ ssize_t vfs_copy_file_range(struct file *file_in, loff_t pos_in, ret = mnt_want_write_file(file_out); if (ret) return ret; + current->in_unprivileged_vfs++; ret = -EOPNOTSUPP; if (file_out->f_op->copy_file_range) @@ -1521,6 +1532,7 @@ ssize_t vfs_copy_file_range(struct file *file_in, loff_t pos_in, ret = do_splice_direct(file_in, &pos_in, file_out, &pos_out, len > MAX_RW_COUNT ? MAX_RW_COUNT : len, 0); + current->in_unprivileged_vfs--; if (ret > 0) { fsnotify_access(file_in); add_rchar(current, ret); diff --git a/fs/splice.c b/fs/splice.c index dd9bf7e..5fcad56 100644 --- a/fs/splice.c +++ b/fs/splice.c @@ -1134,7 +1134,7 @@ static long do_splice_to(struct file *in, loff_t *ppos, { ssize_t (*splice_read)(struct file *, loff_t *, struct pipe_inode_info *, size_t, unsigned int); - int ret; + long ret; if (unlikely(!(in->f_mode & FMODE_READ))) return -EBADF; @@ -1151,7 +1151,11 @@ static long do_splice_to(struct file *in, loff_t *ppos, else splice_read = default_file_splice_read; - return splice_read(in, ppos, pipe, len, flags); + current->in_unprivileged_vfs++; + ret = splice_read(in, ppos, pipe, len, flags); + current->in_unprivileged_vfs--; + + return ret; } /** @@ -1334,7 +1338,9 @@ long do_splice_direct(struct file *in, loff_t *ppos, struct file *out, if (unlikely(ret < 0)) return ret; + current->in_unprivileged_vfs++; ret = splice_direct_to_actor(in, &sd, direct_splice_actor); + current->in_unprivileged_vfs--; if (ret > 0) *ppos = sd.pos; @@ -1401,7 +1407,9 @@ static long do_splice(struct file *in, loff_t __user *off_in, return ret; file_start_write(out); + current->in_unprivileged_vfs++; ret = do_splice_from(ipipe, out, &offset, len, flags); + current->in_unprivileged_vfs--; file_end_write(out); if (!off_out) diff --git a/include/linux/sched.h b/include/linux/sched.h index e4bf894..6094720 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1473,6 +1473,10 @@ struct task_struct { atomic_t usage; unsigned int flags; /* per process flags, defined below */ unsigned int ptrace; + /* depth of VFS read/write; non-zero values let certain privilege checks + * fail with a warning + */ + unsigned int in_unprivileged_vfs; #ifdef CONFIG_SMP struct llist_node wake_entry; diff --git a/kernel/ptrace.c b/kernel/ptrace.c index b311ca5..d839919 100644 --- a/kernel/ptrace.c +++ b/kernel/ptrace.c @@ -302,6 +302,13 @@ ok: bool ptrace_may_access(struct task_struct *task, unsigned int mode) { int err; + + /* If you have to check for ptrace access from a VFS method, use + * ptrace_may_access_noncurrent() instead. + */ + if (WARN_ON(current->in_unprivileged_vfs != 0)) + return false; + task_lock(task); err = __ptrace_may_access(task, mode, current_cred(), ¤t->self_privunit_id);