tcp: fix a signed-integer-overflow bug in tcp_add_backlog()

mainline inclusion
from mainline-v6.1-rc3
commit ec791d81
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I5XG7S


CVE: NA

--------------------------------

The type of sk_rcvbuf and sk_sndbuf in struct sock is int, and
in tcp_add_backlog(), the variable limit is caculated by adding
sk_rcvbuf, sk_sndbuf and 64 * 1024, it may exceed the max value
of int and overflow. This patch reduces the limit budget by
halving the sndbuf to solve this issue since ACK packets are much
smaller than the payload.

Fixes: c9c33212 ("tcp: add tcp_add_backlog()")
Signed-off-by: Lu Wei <luwei32@huawei.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Acked-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

conflict:
	net/ipv4/tcp_ipv4.c

Signed-off-by: Lu Wei <luwei32@huawei.com>
Reviewed-by: Yue Haibing <yuehaibing@huawei.com>
Signed-off-by: Yongqiang Liu <liuyongqiang13@huawei.com>