[RFC PATCH v2 09/48] tcp: Make sendmsg(MSG_SPLICE_PAGES) copy unspliceable data

David Howells
2023-03-29T14:16:56Z

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
tcp_sendmsg() copy it.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Eric Dumazet <edumazet@google.com>
cc: "David S. Miller" <davem@davemloft.net>
cc: Jakub Kicinski <kuba@kernel.org>
cc: Paolo Abeni <pabeni@redhat.com>
cc: Jens Axboe <axboe@kernel.dk>
cc: Matthew Wilcox <willy@infradead.org>
cc: netdev@vger.kernel.org
---
net/ipv4/tcp.c | 28 +++++++++++++++++++++++++---
1 file changed, 25 insertions(+), 3 deletions(-)

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 910b327c236e..6ef0518eb706 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -1417,10 +1417,10 @@ int tcp_sendmsg_locked(struct sock *sk, struct msghdr *msg, size_t size)
goto do_error;
copy = err;
} else if (zc == 2) {
- /* Splice in data. */
+ /* Splice in data if we can; copy if we can't. */
struct page *page = NULL, **pages = &page;
size_t off = 0, part;
- bool can_coalesce;
+ bool can_coalesce, put = false;
int i = skb_shinfo(skb)->nr_frags;

copy = iov_iter_extract_pages(&msg->msg_iter, &pages,
@@ -1447,12 +1447,34 @@ int tcp_sendmsg_locked(struct sock *sk, struct msghdr *msg, size_t size)
goto wait_for_space;
copy = part;

+ 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) {
+ iov_iter_revert(&msg->msg_iter, copy);
+ err = copy ?: -ENOMEM;
+ goto do_error;
+ }
+ page = virt_to_page(q);
+ off = offset_in_page(q);
+ put = true;
+ can_coalesce = false;
+ }
+
if (can_coalesce) {
skb_frag_size_add(&skb_shinfo(skb)->frags[i - 1], copy);
} else {
- get_page(page);
+ if (!put)
+ get_page(page);
+ put = false;
skb_fill_page_desc_noacc(skb, i, page, off, copy);
}
+ if (put)
+ put_page(page);
page = NULL;

if (!(flags & MSG_NO_SHARED_FRAGS))