From c476b3908b73ae362945b9d14d620c0a09a8c539 Mon Sep 17 00:00:00 2001
From: Amulya Y <ayarlagadda@nvidia.com>
Date: Thu, 5 Apr 2018 14:40:20 -0700
Subject: proc:prevent /proc/PID/environ access until ready

If /proc/<PID>/environ gets read before the envp[] array is fully set up
in create_{aout,elf,elf_fdpic,flat}_tables(), we might end up trying to
read more bytes than are actually written, as env_start will already be
set but env_end will still be zero, making the range calculation
underflow, allowing to read beyond the end of what has been written.

Fix this as it is done for /proc/<PID>/cmdline by testing env_end for
zero.  It is, apparently, intentionally set last in create_*_tables().

This bug was found by the PaX size_overflow plugin that detected the
arithmetic underflow of 'this_len = env_end - (env_start + src)' when
env_end is still zero.

The expected consequence is that userland trying to access
/proc/<PID>/environ of a not yet fully set up process may get
inconsistent data as we're in the middle of copying in the environment
variables.

Bug 1823317
Bug 1935735

Change-Id: I38356eb68ffd1294f1f1250fb328bd01a3b37158
Fixes: https://forums.grsecurity.net/viewtopic.php?f=3&t=4363
Fixes: https://bugzilla.kernel.org/show_bug.cgi?id=116461
Signed-off-by: Mathias Krause <minipli@googlemail.com>
Cc: Emese Revfy <re.emese@gmail.com>
Cc: Pax Team <pageexec@freemail.hu>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Mateusz Guzik <mguzik@redhat.com>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Cyrill Gorcunov <gorcunov@openvz.org>
Cc: Jarod Wilson <jarod@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Gagan Grover <ggrover@nvidia.com>
Signed-off-by: Amulya Yarlagadda <ayarlagadda@nvidia.com>
Reviewed-on: http://git-master/r/1259930
(cherry picked from commit 78d40f25b8e090782ca6b0c6051020557d373c92)
Reviewed-on: https://git-master.nvidia.com/r/1690302
Reviewed-by: Automatic_Commit_Validation_User
GVS: Gerrit_Virtual_Submit
Reviewed-by: Bibek Basu <bbasu@nvidia.com>
Reviewed-by: Winnie Hsu <whsu@nvidia.com>
---
 fs/proc/base.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

(limited to 'fs')

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 4823113f2584..464df13a1c19 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -46,7 +46,7 @@
  *  Paul Mundt <paul.mundt@nokia.com>:
  *  Overall revision about smaps.
  *
- * Copyright (c) 2013, NVIDIA CORPORATION.  All rights reserved.
+ * Copyright (c) 2018, NVIDIA CORPORATION.  All rights reserved.
  */
 
 #include <asm/uaccess.h>
@@ -857,7 +857,8 @@ static ssize_t environ_read(struct file *file, char __user *buf,
 	int ret = 0;
 	struct mm_struct *mm = file->private_data;
 
-	if (!mm)
+	/* Ensure the process spawned far enough to have an environment. */
+	if (!mm || !mm->env_end)
 		return 0;
 
 	page = (char *)__get_free_page(GFP_TEMPORARY);
-- 
cgit v1.2.3