Subject: [PATCH net-next] ip, ip6: Fix splice to raw and ping sockets

From: David Howells <[email-masked]>
Date: Wed, 14 Jun 2023 09:04:16 +0100

Splicing to SOCK_RAW sockets may set MSG_SPLICE_PAGES, but in such a case,
__ip_append_data() will call skb_splice_from_iter() to access the 'from'
data, assuming it to point to a msghdr struct with an iter, instead of
using the provided getfrag function to access it.

In the case of raw_sendmsg(), however, this is not the case and 'from' will
point to a raw_frag_vec struct and raw_getfrag() will be the frag-getting
function.  A similar issue may occur with rawv6_sendmsg().

Fix this by ignoring MSG_SPLICE_PAGES if getfrag != ip_generic_getfrag as
ip_generic_getfrag() expects "from" to be a msghdr*, but the other getfrags
don't.  Note that this will prevent MSG_SPLICE_PAGES from being effective
for udplite.

This likely affects ping sockets too.  udplite looks like it should be okay
as it expects "from" to be a msghdr.

Signed-off-by: David Howells <[email-masked]>
Reported-by: [email-masked]
Link: https://lore.kernel.org/r/[email-masked]/
Fixes: 2dc334f1a63a ("splice, net: Use sendmsg(MSG_SPLICE_PAGES) rather than ->sendpage()")
Tested-by: [email-masked]
cc: Willem de Bruijn <[email-masked]>
cc: David Ahern <[email-masked]>
cc: "David S. Miller" <[email-masked]>
cc: Eric Dumazet <[email-masked]>
cc: Jakub Kicinski <[email-masked]>
cc: Paolo Abeni <[email-masked]>
cc: Jens Axboe <[email-masked]>
cc: Matthew Wilcox <[email-masked]>
cc: [email-masked]
---
 net/ipv4/ip_output.c  |    3 ++-
 net/ipv6/ip6_output.c |    3 ++-
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
index 244fb9365d87..4b39ea99f00b 100644
--- a/net/ipv4/ip_output.c
+++ b/net/ipv4/ip_output.c
@@ -1040,7 +1040,8 @@ static int __ip_append_data(struct sock *sk,
 	} else if ((flags & MSG_SPLICE_PAGES) && length) {
 		if (inet->hdrincl)
 			return -EPERM;
-		if (rt->dst.dev->features & NETIF_F_SG)
+		if (rt->dst.dev->features & NETIF_F_SG &&
+		    getfrag == ip_generic_getfrag)
 			/* We need an empty buffer to attach stuff to */
 			paged = true;
 		else
diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
index c722cb881b2d..dd845139882c 100644
--- a/net/ipv6/ip6_output.c
+++ b/net/ipv6/ip6_output.c
@@ -1592,7 +1592,8 @@ static int __ip6_append_data(struct sock *sk,
 	} else if ((flags & MSG_SPLICE_PAGES) && length) {
 		if (inet_sk(sk)->hdrincl)
 			return -EPERM;
-		if (rt->dst.dev->features & NETIF_F_SG)
+		if (rt->dst.dev->features & NETIF_F_SG &&
+		    getfrag == ip_generic_getfrag)
 			/* We need an empty buffer to attach stuff to */
 			paged = true;
 		else