[PATCH net v2] net: devmem: prevent net-iov / page mixing

We should either have net_iov or page backed frags in a single skb,
otherwise it blows up down the stack. Don't allow mixing in
zerocopy_fill_skb_from_devmem().

Fixes: bd61848900bff ("net: devmem: Implement TX path")
Cc: stable@vger.kernel.org
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---

v2: EEXIST -> EFAULT, as skb_zerocopy_iter_stream() doesn't handle
    the former + for consistency. 

 net/core/datagram.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/core/datagram.c b/net/core/datagram.c
index c285c6465923..173b5d97bd40 100644
--- a/net/core/datagram.c
+++ b/net/core/datagram.c

@@ -712,6 +712,9 @@ zerocopy_fill_skb_from_devmem(struct sk_buff *skb, struct iov_iter *from,
 	size_t virt_addr, size, off;
 	struct net_iov *niov;
 
+	if (i && skb_frags_readable(skb))
+		return -EFAULT;
+
 	/* Devmem filling works by taking an IOVEC from the user where the
 	 * iov_addrs are interpreted as an offset in bytes into the dma-buf to
 	 * send from. We do not support other iter types.

-- 
2.54.0