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Date: Sun, 22 Jul 2012 22:00:49 +0200
From: Oleg Nesterov <oleg@...hat.com>
To: Djalal Harouni <tixxdz@...ndz.org>
Cc: linux-kernel@...r.kernel.org, kernel-hardening@...ts.openwall.com,
Al Viro <viro@...iv.linux.org.uk>,
Andrew Morton <akpm@...ux-foundation.org>,
Vasiliy Kulikov <segoon@...nwall.com>,
WANG Cong <xiyou.wangcong@...il.com>,
Solar Designer <solar@...nwall.com>, Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH] proc: do not allow negative offsets on
/proc/<pid>/environ
On 07/22, Djalal Harouni wrote:
>
> __mem_open() which is called by both /proc/<pid>/environ and
> /proc/<pid>/mem ->open() handlers will allow the use of negative offsets.
> /proc/<pid>/mem has negative offsets but not /proc/<pid>/environ.
Probablt the patch makes sense, but I can't understand the changelog...
> Allowing negative offsets on /proc/<pid>/environ can turn it to act like
> /proc/<pid>/mem. A negative offset will pass the
> fs/read_write.c:lseek_execute() and the environ_read() checks and will
> point to another VMA.
which VMA?
environ_read() can only read the memory from [env_start, env_end], and
it should check *ppos anyway to ensure it doesn't read something else.
> static int mem_open(struct inode *inode, struct file *file)
> {
> - return __mem_open(inode, file, PTRACE_MODE_ATTACH);
> + int ret = __mem_open(inode, file, PTRACE_MODE_ATTACH);
> + if (!ret)
> + /* OK to pass negative loff_t, we can catch out-of-range */
> + file->f_mode |= FMODE_UNSIGNED_OFFSET;
> +
> + return ret;
I guess you can set FMODE_UNSIGNED_OFFSET unconditionally, it doesn't
matter if __mem_open() fails. But I won't insist.
Oleg.
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