Re: [BUG] acess_ok() missing from zerocopy_sg_from_iovec()

[Eric Dumazet <eric.dumazet@gmail.com>]

On Mon, 2013-06-03 at 17:34 -0700, Eric Dumazet wrote:
> It looks like access_ok(VERIFY_READ, base, len) checks are missing in
> drivers/net/tun.c & drivers/net/macvtap.c before the
> get_user_pages_fast() calls.
> 
> Or am I missing something ?
> 

Patch would be :

[PATCH] tun/macvtap: use access_ok(VERIFY_READ)

Zero copy is good if only we make all needed security checks.

Signed-off-by: Eric Dumazet <edumazet@google.com>
---

diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c
index 59e9605..d793b7d 100644
--- a/drivers/net/macvtap.c
+++ b/drivers/net/macvtap.c
@@ -522,6 +522,8 @@ static int zerocopy_sg_from_iovec(struct sk_buff *skb, const struct iovec *from,
 		size = ((base & ~PAGE_MASK) + len + ~PAGE_MASK) >> PAGE_SHIFT;
 		if (i + size > MAX_SKB_FRAGS)
 			return -EMSGSIZE;
+		if (!access_ok(VERIFY_READ, base, len))
+			return -EFAULT;
 		num_pages = get_user_pages_fast(base, size, 0, &page[i]);
 		if (num_pages != size) {
 			for (i = 0; i < num_pages; i++)
diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 89776c5..7a7b3b1 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -1008,6 +1008,8 @@ static int zerocopy_sg_from_iovec(struct sk_buff *skb, const struct iovec *from,
 		size = ((base & ~PAGE_MASK) + len + ~PAGE_MASK) >> PAGE_SHIFT;
 		if (i + size > MAX_SKB_FRAGS)
 			return -EMSGSIZE;
+		if (!access_ok(VERIFY_READ, base, len))
+			return -EFAULT;
 		num_pages = get_user_pages_fast(base, size, 0, &page[i]);
 		if (num_pages != size) {
 			for (i = 0; i < num_pages; i++)