linux-kernel - [PATCH 4.9 059/101] tcp: fix over estimation in sk_forced_mem

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Date:   Tue, 23 Aug 2022 10:03:32 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Eric Dumazet <edumazet@...gle.com>,
        Soheil Hassas Yeganeh <soheil@...gle.com>,
        Shakeel Butt <shakeelb@...gle.com>,
        Wei Wang <weiwan@...gle.com>,
        "David S. Miller" <davem@...emloft.net>
Subject: [PATCH 4.9 059/101] tcp: fix over estimation in sk_forced_mem_schedule()

From: Eric Dumazet <edumazet@...gle.com>

commit c4ee118561a0f74442439b7b5b486db1ac1ddfeb upstream.

sk_forced_mem_schedule() has a bug similar to ones fixed
in commit 7c80b038d23e ("net: fix sk_wmem_schedule() and
sk_rmem_schedule() errors")

While this bug has little chance to trigger in old kernels,
we need to fix it before the following patch.

Fixes: d83769a580f1 ("tcp: fix possible deadlock in tcp_send_fin()")
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Acked-by: Soheil Hassas Yeganeh <soheil@...gle.com>
Reviewed-by: Shakeel Butt <shakeelb@...gle.com>
Reviewed-by: Wei Wang <weiwan@...gle.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 net/ipv4/tcp_output.c |    7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -2986,11 +2986,12 @@ begin_fwd:
  */
 void sk_forced_mem_schedule(struct sock *sk, int size)
 {
-	int amt;
+	int delta, amt;
 
-	if (size <= sk->sk_forward_alloc)
+	delta = size - sk->sk_forward_alloc;
+	if (delta <= 0)
 		return;
-	amt = sk_mem_pages(size);
+	amt = sk_mem_pages(delta);
 	sk->sk_forward_alloc += amt * SK_MEM_QUANTUM;
 	sk_memory_allocated_add(sk, amt);