From: Mateusz Guzik <mguzik@redhat.com>
To: Mathias Krause <minipli@googlemail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
linux-kernel@vger.kernel.org, Emese Revfy <re.emese@gmail.com>,
Pax Team <pageexec@freemail.hu>,
Al Viro <viro@zeniv.linux.org.uk>,
Alexey Dobriyan <adobriyan@gmail.com>,
Cyrill Gorcunov <gorcunov@openvz.org>,
Jarod Wilson <jarod@redhat.com>
Subject: Re: [PATCH] proc: prevent accessing /proc/<PID>/environ until it's ready
Date: Thu, 28 Apr 2016 21:20:10 +0200 [thread overview]
Message-ID: <20160428192009.lqoyl65l4lhnmecs@mguzik> (raw)
In-Reply-To: <1461870258-17970-1-git-send-email-minipli@googlemail.com>
On Thu, Apr 28, 2016 at 09:04:18PM +0200, Mathias Krause wrote:
> 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.
>
> Reported-at: https://forums.grsecurity.net/viewtopic.php?f=3&t=4363
> Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=116461
> ---
> fs/proc/base.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/fs/proc/base.c b/fs/proc/base.c
> index 4f764c2ac1a5..45f2162e55b2 100644
> --- a/fs/proc/base.c
> +++ b/fs/proc/base.c
> @@ -955,7 +955,8 @@ static ssize_t environ_read(struct file *file, char __user *buf,
> struct mm_struct *mm = file->private_data;
> unsigned long env_start, env_end;
>
> - 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);
In this case get_cmdline in mm/util.c should also be patched for
completness. It tests for arg_end, but later accesses env_end.
--
Mateusz Guzik
next prev parent reply other threads:[~2016-04-28 19:20 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-04-28 19:04 [PATCH] proc: prevent accessing /proc/<PID>/environ until it's ready Mathias Krause
2016-04-28 19:20 ` Mateusz Guzik [this message]
2016-04-28 19:36 ` Mathias Krause
2016-04-29 10:11 ` Alexey Dobriyan
2016-04-28 19:28 ` Cyrill Gorcunov
2016-04-28 21:26 ` Andrew Morton
2016-04-29 5:59 ` Mathias Krause
2016-04-28 21:30 ` Andrew Morton
2016-04-29 6:02 ` Mathias Krause
2016-04-29 10:25 ` Alexey Dobriyan
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