linux-kernel - Re: [PATCH] kernel 2.6.24.1 still vulnerable to the vmsplice local root exploit

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Date:	Sun, 10 Feb 2008 13:22:50 +0100
From:	Bastian Blank <bastian@...di.eu.org>
To:	Niki Denev <ndenev@...il.com>, Willy Tarreau <w@....eu>
Cc:	linux-kernel@...r.kernel.org, jens.axboe@...cle.com
Subject: Re: [PATCH] kernel 2.6.24.1 still vulnerable to the vmsplice local root exploit

On Sun, Feb 10, 2008 at 04:40:53AM -0500, Niki Denev wrote:
> this fixed the problem for me (kernel 2.6.24.1) :
> It appears that the initial patch checked the input to vmsplice_to_user,
> but the exploit used vmsplice_to_pipe which remained open to the attack.

This patch is broken. It opens the old hole again.

> @@ -1450,6 +1454,31 @@
>  		.ops = &user_page_pipe_buf_ops,
>  	};
> 
> +	error = ret = 0;
> +
> +	/*
> +	 * Get user address base and length for this iovec.
> +	 */
> +	error = get_user(base, &iov->iov_base);
> +	if (unlikely(error))
> +		return error;
> +	error = get_user(len, &iov->iov_len);
> +	if (unlikely(error))
> +		return error;

iov is unchecked.

> +	if (unlikely(!access_ok(VERIFY_WRITE, base, len))) {
> +		return -EFAULT;
> +	}

Use VERIFY_READ and this only checks the first entry.

I checked the following patch and it at least fixes the known exploit.

diff --git a/fs/splice.c b/fs/splice.c
index 14e2262..80beb2b 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -1237,6 +1237,11 @@ static int get_iovec_page_array(const struct iovec __user *iov,
 		if (unlikely(!base))
 			break;
 
+		if (!access_ok(VERIFY_READ, base, len)) {
+			error = -EFAULT;
+			break;
+		}
+
 		/*
 		 * Get this base offset and number of pages, then map
 		 * in the user pages.
-- 
Even historians fail to learn from history -- they repeat the same mistakes.
		-- John Gill, "Patterns of Force", stardate 2534.7
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