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 04:40:53 -0500
From:	"Niki Denev" <ndenev@...il.com>
To:	"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 Feb 10, 2008 1:38 AM, Niki Denev <ndenev@...il.com> wrote:
>
> On Feb 10, 2008 8:32 AM, Willy Tarreau <w@....eu> wrote:
> > On Sun, Feb 10, 2008 at 08:04:35AM +0200, Niki Denev wrote:
> > > Hi,
> > >
> > > As the subject says the 2.6.24.1 is still vulnerable to the vmsplice
> > > local root exploit.
> >
> > Yes indeed, that's quite bad. 2.6.24-git is still vulnerable too, and
> > also contains the fix :-(
> >
> > CC'd Jens as he worked on the fix.
> >
> > Willy
> >
> >
>
> I was unable to gain root on 2.6.24-git20
> but after several segfaults when executing the exploit continously
> the machine crashes.
>
> --Niki
>

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.

--- fs/splice.c.orig	2008-02-08 21:55:30.000000000 +0200
+++ fs/splice.c	2008-02-10 11:32:50.000000000 +0200
@@ -1443,6 +1443,10 @@
 	struct pipe_inode_info *pipe;
 	struct page *pages[PIPE_BUFFERS];
 	struct partial_page partial[PIPE_BUFFERS];
+	int error;
+	long ret;
+	void __user *base;
+	size_t len;
 	struct splice_pipe_desc spd = {
 		.pages = pages,
 		.partial = partial,
@@ -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;
+
+	/*
+	 * Sanity check this iovec. 0 read succeeds.
+	 */
+	if (unlikely(!len))
+		return 0;
+	if (unlikely(!base)) {
+		return -EFAULT;	
+	}
+
+	if (unlikely(!access_ok(VERIFY_WRITE, base, len))) {
+		return -EFAULT;
+	}
+
 	pipe = pipe_info(file->f_path.dentry->d_inode);
 	if (!pipe)
 		return -EBADF;
--
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