SUNRPC: fix sign error causing rpcsec_gss drops

stable inclusion
from stable-5.10.73
commit 9aac782ab0ab0fd0a8e507a6294359c2f5cf182d
bugzilla: 182983 https://gitee.com/openeuler/kernel/issues/I4I3M0

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9aac782ab0ab0fd0a8e507a6294359c2f5cf182d

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

commit 2ba5acfb upstream.

If sd_max is unsigned, then sd_max - GSS_SEQ_WIN is a very large number
whenever sd_max is less than GSS_SEQ_WIN, and the comparison:

	seq_num <= sd->sd_max - GSS_SEQ_WIN

in gss_check_seq_num is pretty much always true, even when that's
clearly not what was intended.

This was causing pynfs to hang when using krb5, because pynfs uses zero
as the initial gss sequence number.  That's perfectly legal, but this
logic error causes knfsd to drop the rpc in that case.  Out-of-order
sequence IDs in the first GSS_SEQ_WIN (128) calls will also cause this.

Fixes: 10b9d99a ("SUNRPC: Augment server-side rpcgss tracepoints")
Cc: stable@vger.kernel.org
Signed-off-by: NJ. Bruce Fields <bfields@redhat.com>
Signed-off-by: NChuck Lever <chuck.lever@oracle.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: NChen Jun <chenjun102@huawei.com>
Acked-by: NWeilong Chen <chenweilong@huawei.com>
Signed-off-by: NChen Jun <chenjun102@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

net/sunrpc/auth_gss/svcauth_gss.c

@@ -643,7 +643,7 @@ static bool gss_check_seq_num(const struct svc_rqst *rqstp, struct rsc *rsci,
 		}
 		__set_bit(seq_num % GSS_SEQ_WIN, sd->sd_win);
 		goto ok;
-	} else if (seq_num <= sd->sd_max - GSS_SEQ_WIN) {
+	} else if (seq_num + GSS_SEQ_WIN <= sd->sd_max) {
 		goto toolow;
 	}
 	if (__test_and_set_bit(seq_num % GSS_SEQ_WIN, sd->sd_win))