linux-kernel - [RFC PATCH v2 17/48] ip, udp: Make sendmsg(MSG_SPLICE

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Message-Id: <20230329141354.516864-18-dhowells@redhat.com>
Date:   Wed, 29 Mar 2023 15:13:23 +0100
From:   David Howells <dhowells@...hat.com>
To:     Matthew Wilcox <willy@...radead.org>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>
Cc:     David Howells <dhowells@...hat.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Christoph Hellwig <hch@...radead.org>,
        Jens Axboe <axboe@...nel.dk>, Jeff Layton <jlayton@...nel.org>,
        Christian Brauner <brauner@...nel.org>,
        Chuck Lever III <chuck.lever@...cle.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        netdev@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Willem de Bruijn <willemdebruijn.kernel@...il.com>
Subject: [RFC PATCH v2 17/48] ip, udp: Make sendmsg(MSG_SPLICE_PAGES) copy unspliceable data

If sendmsg() with MSG_SPLICE_PAGES encounters a page that shouldn't be
spliced - a slab page, for instance, or one with a zero count - make
__ip_append_data() copy it.

Signed-off-by: David Howells <dhowells@...hat.com>
cc: Willem de Bruijn <willemdebruijn.kernel@...il.com>
cc: "David S. Miller" <davem@...emloft.net>
cc: Eric Dumazet <edumazet@...gle.com>
cc: Jakub Kicinski <kuba@...nel.org>
cc: Paolo Abeni <pabeni@...hat.com>
cc: Jens Axboe <axboe@...nel.dk>
cc: Matthew Wilcox <willy@...radead.org>
cc: netdev@...r.kernel.org
---
 net/ipv4/ip_output.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
index 07736da70eab..e4aeaab704c8 100644
--- a/net/ipv4/ip_output.c
+++ b/net/ipv4/ip_output.c
@@ -1263,6 +1263,7 @@ static int __ip_append_data(struct sock *sk,
 			struct msghdr *msg = from;
 			struct page *page = NULL, **pages = &page;
 			size_t off;
+			bool put = false;
 
 			copy = iov_iter_extract_pages(&msg->msg_iter, &pages,
 						      copy, 1, 0, &off);
@@ -1271,7 +1272,25 @@ static int __ip_append_data(struct sock *sk,
 				goto error;
 			}
 
+			if (!sendpage_ok(page)) {
+				const void *p = kmap_local_page(page);
+				void *q;
+
+				q = page_frag_memdup(NULL, p + off, copy,
+						     sk->sk_allocation, ULONG_MAX);
+				kunmap_local(p);
+				if (!q) {
+					err = copy ?: -ENOMEM;
+					goto error;
+				}
+				page = virt_to_page(q);
+				off = offset_in_page(q);
+				put = true;
+			}
+
 			err = skb_append_pagefrags(skb, page, off, copy);
+			if (put)
+				put_page(page);
 			if (err < 0)
 				goto error;