net: rds: Fix possible NULL-pointer dereference

stable inclusion
from stable-v5.10.198
commit f515112e833791001aaa8ab886af3ca78503617f
category: bugfix
bugzilla: https://gitee.com/src-openeuler/kernel/issues/I95ATK
CVE: CVE-2023-52573

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f515112e833791001aaa8ab886af3ca78503617f



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[ Upstream commit f1d95df0 ]

In rds_rdma_cm_event_handler_cmn() check, if conn pointer exists
before dereferencing it as rdma_set_service_type() argument

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Fixes: fd261ce6 ("rds: rdma: update rdma transport for tos")
Signed-off-by: Artem Chernyshev <artem.chernyshev@red-soft.ru>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Zhengchao Shao <shaozhengchao@huawei.com>