From: Eric Dumazet

Sent: 06 August 2020 23:21

On 7/22/20 11:09 PM, Christoph Hellwig wrote:

quoted

Rework the remaining setsockopt code to pass a sockptr_t instead of a
plain user pointer.  This removes the last remaining set_fs(KERNEL_DS)
outside of architecture specific code.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Stefan Schmidt <stefan@datenfreihafen.org> [ieee802154]
---

...

quoted

diff --git a/net/ipv6/raw.c b/net/ipv6/raw.c
index 594e01ad670aa6..874f01cd7aec42 100644
--- a/net/ipv6/raw.c
+++ b/net/ipv6/raw.c

@@ -972,13 +972,13 @@ static int rawv6_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 }

...

quoted

 static int do_rawv6_setsockopt(struct sock *sk, int level, int optname,
-			    char __user *optval, unsigned int optlen)
+			       sockptr_t optval, unsigned int optlen)
 {
 	struct raw6_sock *rp = raw6_sk(sk);
 	int val;

-	if (get_user(val, (int __user *)optval))
+	if (copy_from_sockptr(&val, optval, sizeof(val)))
 		return -EFAULT;

converting get_user(...)   to  copy_from_sockptr(...) really assumed the optlen
has been validated to be >= sizeof(int) earlier.

Which is not always the case, for example here.

User application can fool us passing optlen=0, and a user pointer of exactly TASK_SIZE-1

Won't the user pointer force copy_from_sockptr() to call
copy_from_user() which will then do access_ok() on the entire
range and so return -EFAULT.

The only problems arise if the kernel code adds an offset to the
user address.
And the later patch added an offset to the copy functions.

	David

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)