[PATCH]: SCTP length validation.

I just checked in the following SCTP bug fix to net-2.6 and will make
sure it gets into -stable as well.

sctp: Make sure N * sizeof(union sctp_addr) does not overflow.

As noticed by Gabriel Campana, the kmalloc() length arg
passed in by sctp_getsockopt_local_addrs_old() can overflow
if ->addr_num is large enough.

Therefore, enforce an appropriate limit.

Signed-off-by: David S. Miller <davem@davemloft.net>
---
 net/sctp/socket.c |    4 +++-
 1 files changed, 3 insertions(+), 1 deletions(-)

diff --git a/net/sctp/socket.c b/net/sctp/socket.c
index e7e3baf..0dbcde6 100644
--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c

@@ -4401,7 +4401,9 @@ static int sctp_getsockopt_local_addrs_old(struct sock *sk, int len,
 	if (copy_from_user(&getaddrs, optval, len))
 		return -EFAULT;
 
-	if (getaddrs.addr_num <= 0) return -EINVAL;
+	if (getaddrs.addr_num <= 0 ||
+	    getaddrs.addr_num >= (INT_MAX / sizeof(union sctp_addr)))
+		return -EINVAL;
 	/*
 	 *  For UDP-style sockets, id specifies the association to query.
 	 *  If the id field is set to the value '0' then the locally bound

-- 
1.5.6

David Miller wrote:

I just checked in the following SCTP bug fix to net-2.6 and will make
sure it gets into -stable as well.

sctp: Make sure N * sizeof(union sctp_addr) does not overflow.

As noticed by Gabriel Campana, the kmalloc() length arg
passed in by sctp_getsockopt_local_addrs_old() can overflow
if ->addr_num is large enough.

Therefore, enforce an appropriate limit.

Hi David

The same vulnerability also exists in sctp_getsockopt_peer_addrs_old().
It's a bit more difficult to trigger since there is a dependency on
the peer being multihomed as well, but it's still possible to cause the
overwrite.

-vlad

From: Vlad Yasevich <redacted>
Date: Sat, 21 Jun 2008 11:55:19 -0400

The same vulnerability also exists in sctp_getsockopt_peer_addrs_old().
It's a bit more difficult to trigger since there is a dependency on
the peer being multihomed as well, but it's still possible to cause the
overwrite.

I can't see how that's possible.  This case looks harmless to
me.

The kernel side accesses are perfectly protected.  The kernel
will only access the actual address list stored via:

	list_for_each_entry(from, &asoc->peer.transport_addr_list,
				transports) {
 ...
		cnt ++;
		if (cnt >= getaddrs.addr_num) break;
	}
	getaddrs.addr_num = cnt;

Copies are only made to userspace, and the given ->addr_num only
serves as an early break-out from that loop.  I mean, take a look,
those lines in the above are the only aaccesses made to the user's
provided addr_num value.

There is no possibility to use strange ->addr_num values
in order to read or write kernel memory outside of the
intended bounds.

I don't even see any value to adding new checks here.

David Miller wrote:

From: Vlad Yasevich <redacted>
Date: Sat, 21 Jun 2008 11:55:19 -0400

quoted

The same vulnerability also exists in sctp_getsockopt_peer_addrs_old().
It's a bit more difficult to trigger since there is a dependency on
the peer being multihomed as well, but it's still possible to cause the
overwrite.

I can't see how that's possible.  This case looks harmless to
me.

The kernel side accesses are perfectly protected.  The kernel
will only access the actual address list stored via:

	list_for_each_entry(from, &asoc->peer.transport_addr_list,
				transports) {
 ...
		cnt ++;
		if (cnt >= getaddrs.addr_num) break;
	}
	getaddrs.addr_num = cnt;

Copies are only made to userspace, and the given ->addr_num only
serves as an early break-out from that loop.  I mean, take a look,
those lines in the above are the only aaccesses made to the user's
provided addr_num value.

There is no possibility to use strange ->addr_num values
in order to read or write kernel memory outside of the
intended bounds.

I don't even see any value to adding new checks here.

You are right.  I didn't look far enough.  Since there is no kmalloc(),
the overflow of kernel memory is not possible, and copy_to_user should
take care of any overflows of the user memory.

-vlad

From: Vlad Yasevich <redacted>
Date: Mon, 23 Jun 2008 11:59:43 -0400

David Miller wrote:

quoted

From: Vlad Yasevich <redacted>
Date: Sat, 21 Jun 2008 11:55:19 -0400

quoted

The same vulnerability also exists in sctp_getsockopt_peer_addrs_old().
It's a bit more difficult to trigger since there is a dependency on
the peer being multihomed as well, but it's still possible to cause the
overwrite.

I can't see how that's possible.  This case looks harmless to
me.

The kernel side accesses are perfectly protected.  The kernel
will only access the actual address list stored via:

 ...

You are right.  I didn't look far enough.  Since there is no kmalloc(),
the overflow of kernel memory is not possible, and copy_to_user should
take care of any overflows of the user memory.

Thanks for double-checking my analysis Vlad.