linux-kernel - [PATCH 3/6] macvtap: zerocopy: validate vector length before pinning user pages

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Message-ID: <20120416060807.14140.96229.stgit@intel-e5620-16-2.englab.nay.redhat.com>
Date:	Mon, 16 Apr 2012 14:08:07 +0800
From:	Jason Wang <jasowang@...hat.com>
To:	netdev@...r.kernel.org, xma@...ibm.com, davem@...emloft.net,
	linux-kernel@...r.kernel.org, mst@...hat.com
Cc:	ebiederm@...ssion.com
Subject: [PATCH 3/6] macvtap: zerocopy: validate vector length before pinning
	user pages

Currently we do not validate the vector length before calling
get_user_pages_fast(), host stack would be easily overflowed by
malicious guest driver who give us a descriptor with length greater
than MAX_SKB_FRAGS. Solve this problem by checking the free entries
before trying to pin user pages.

Signed-off-by: Jason Wang <jasowang@...hat.com>
---
 drivers/net/macvtap.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c
index 7cb2684..d197a78 100644
--- a/drivers/net/macvtap.c
+++ b/drivers/net/macvtap.c
@@ -529,6 +529,8 @@ static int zerocopy_sg_from_iovec(struct sk_buff *skb, const struct iovec *from,
 		}
 		base = (unsigned long)from->iov_base + offset;
 		size = ((base & ~PAGE_MASK) + len + ~PAGE_MASK) >> PAGE_SHIFT;
+		if (i + size >= MAX_SKB_FRAGS)
+			return -EFAULT;
 		num_pages = get_user_pages_fast(base, size, 0, &page[i]);
 		if ((num_pages != size) ||
 		    (num_pages > MAX_SKB_FRAGS - skb_shinfo(skb)->nr_frags))

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