Commit f8d9d938 authored by Eric Dumazet's avatar Eric Dumazet Committed by Jakub Kicinski
Browse files

tcp: take care of mixed splice()/sendmsg(MSG_ZEROCOPY) case 



syzbot found that mixing sendpage() and sendmsg(MSG_ZEROCOPY)
calls over the same TCP socket would again trigger the
infamous warning in inet_sock_destruct()

	WARN_ON(sk_forward_alloc_get(sk));

While Talal took into account a mix of regular copied data
and MSG_ZEROCOPY one in the same skb, the sendpage() path
has been forgotten.

We want the charging to happen for sendpage(), because
pages could be coming from a pipe. What is missing is the
downgrading of pure zerocopy status to make sure
sk_forward_alloc will stay synced.

Add tcp_downgrade_zcopy_pure() helper so that we can
use it from the two callers.

Fixes: 9b65b17d ("net: avoid double accounting for pure zerocopy skbs")
Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Reported-by: default avatarsyzbot <syzkaller@googlegroups.com>
Cc: Talal Ahmad <talalahmad@google.com>
Cc: Arjun Roy <arjunroy@google.com>
Cc: Willem de Bruijn <willemb@google.com>
Acked-by: default avatarSoheil Hassas Yeganeh <soheil@google.com>
Link: https://lore.kernel.org/r/20220203225547.665114-1-eric.dumazet@gmail.com


Signed-off-by: default avatarJakub Kicinski <kuba@kernel.org>
parent 40106e00

net/ipv4/tcp.c

+19 −14
Original line number Diff line number Diff line
@@ -937,6 +937,22 @@ void tcp_remove_empty_skb(struct sock *sk) 
	}

}



/* skb changing from pure zc to mixed, must charge zc */

static int tcp_downgrade_zcopy_pure(struct sock *sk, struct sk_buff *skb)

{

	if (unlikely(skb_zcopy_pure(skb))) {

		u32 extra = skb->truesize -

			    SKB_TRUESIZE(skb_end_offset(skb));



		if (!sk_wmem_schedule(sk, extra))

			return -ENOMEM;



		sk_mem_charge(sk, extra);

		skb_shinfo(skb)->flags &= ~SKBFL_PURE_ZEROCOPY;

	}

	return 0;

}



static struct sk_buff *tcp_build_frag(struct sock *sk, int size_goal, int flags,

				      struct page *page, int offset, size_t *size)

{
@@ -972,7 +988,7 @@ static struct sk_buff *tcp_build_frag(struct sock *sk, int size_goal, int flags, 
		tcp_mark_push(tp, skb);

		goto new_segment;

	}

	if (!sk_wmem_schedule(sk, copy))

	if (tcp_downgrade_zcopy_pure(sk, skb) || !sk_wmem_schedule(sk, copy))

		return NULL;



	if (can_coalesce) {
@@ -1320,19 +1336,8 @@ int tcp_sendmsg_locked(struct sock *sk, struct msghdr *msg, size_t size) 


			copy = min_t(int, copy, pfrag->size - pfrag->offset);



			/* skb changing from pure zc to mixed, must charge zc */

			if (unlikely(skb_zcopy_pure(skb))) {

				u32 extra = skb->truesize -

					    SKB_TRUESIZE(skb_end_offset(skb));



				if (!sk_wmem_schedule(sk, extra))

					goto wait_for_space;



				sk_mem_charge(sk, extra);

				skb_shinfo(skb)->flags &= ~SKBFL_PURE_ZEROCOPY;

			}



			if (!sk_wmem_schedule(sk, copy))

			if (tcp_downgrade_zcopy_pure(sk, skb) ||

			    !sk_wmem_schedule(sk, copy))

				goto wait_for_space;



			err = skb_copy_to_page_nocache(sk, &msg->msg_iter, skb,