2017-10-31 13:24:35 -04:00
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From 8148a73c9901a8794a50f950083c00ccf97d43b3 Mon Sep 17 00:00:00 2001
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From: Mathias Krause <minipli@googlemail.com>
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Date: Thu, 5 May 2016 16:22:26 -0700
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Subject: proc: prevent accessing /proc/<PID>/environ until it's ready
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If /proc/<PID>/environ gets read before the envp[] array is fully set up
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in create_{aout,elf,elf_fdpic,flat}_tables(), we might end up trying to
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read more bytes than are actually written, as env_start will already be
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set but env_end will still be zero, making the range calculation
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underflow, allowing to read beyond the end of what has been written.
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Fix this as it is done for /proc/<PID>/cmdline by testing env_end for
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zero. It is, apparently, intentionally set last in create_*_tables().
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This bug was found by the PaX size_overflow plugin that detected the
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arithmetic underflow of 'this_len = env_end - (env_start + src)' when
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env_end is still zero.
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The expected consequence is that userland trying to access
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/proc/<PID>/environ of a not yet fully set up process may get
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inconsistent data as we're in the middle of copying in the environment
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variables.
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Fixes: https://forums.grsecurity.net/viewtopic.php?f=3&t=4363
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Fixes: https://bugzilla.kernel.org/show_bug.cgi?id=116461
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Signed-off-by: Mathias Krause <minipli@googlemail.com>
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Cc: Emese Revfy <re.emese@gmail.com>
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Cc: Pax Team <pageexec@freemail.hu>
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Cc: Al Viro <viro@zeniv.linux.org.uk>
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Cc: Mateusz Guzik <mguzik@redhat.com>
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Cc: Alexey Dobriyan <adobriyan@gmail.com>
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Cc: Cyrill Gorcunov <gorcunov@openvz.org>
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Cc: Jarod Wilson <jarod@redhat.com>
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Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
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Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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---
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fs/proc/base.c | 3 ++-
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1 file changed, 2 insertions(+), 1 deletion(-)
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diff --git a/fs/proc/base.c b/fs/proc/base.c
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index b1755b2..92e37e2 100644
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--- a/fs/proc/base.c
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+++ b/fs/proc/base.c
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@@ -955,7 +955,8 @@ static ssize_t environ_read(struct file *file, char __user *buf,
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struct mm_struct *mm = file->private_data;
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unsigned long env_start, env_end;
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- if (!mm)
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+ /* Ensure the process spawned far enough to have an environment. */
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+ if (!mm || !mm->env_end)
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return 0;
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page = (char *)__get_free_page(GFP_TEMPORARY);
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--
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cgit v1.1
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