net: sched: atm: dont intepret cls results when asked to drop

stable inclusion
from stable-v4.19.269
commit 5374c455ebe6102e3d5f1842c6d8ff72b3ca659f
category: bugfix
bugzilla: 188250, https://gitee.com/src-openeuler/kernel/issues/I6AQG9
CVE: CVE-2023-23455

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=5374c455ebe6102e3d5f1842c6d8ff72b3ca659f



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[ Upstream commit a2965c7b ]

If asked to drop a packet via TC_ACT_SHOT it is unsafe to assume
res.class contains a valid pointer
Fixes: b0188d4d ("[NET_SCHED]: sch_atm: Lindent")

Signed-off-by: Jamal Hadi Salim <jhs@mojatatu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Dong Chenchen <dongchenchen2@huawei.com>
Reviewed-by: Yue Haibing <yuehaibing@huawei.com>
Reviewed-by: Wang Weiyang <wangweiyang2@huawei.com>
Signed-off-by: Yongqiang Liu <liuyongqiang13@huawei.com>