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

On 07/27, Pavel Begunkov wrote:

On 7/27/26 17:46, Stanislav Fomichev wrote:

quoted

On 07/27, Pavel Begunkov wrote:

quoted

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;
+

Maybe we should do -EMSGSIZE? It is already properly plumbed via
skb_zerocopy_iter_stream (and you'll hit 'skb->len == orig_len')
and it hits 'new_segment' in tcp_sendmsg_locked?

I made it consistent with zerocopy_fill_skb_from_iter(), don't see
the point of making it behaving differently from combination to
combination. Do you have some use case for that?

Ah, ok, yeah, that makes sense, let's go with that!

Acked-by: Stanislav Fomichev <sdf@fomichev.me>