[PATCH] SUNRPC: fix sign error causing rpcsec_gss drops

[bfields@fieldses.org (J. Bruce Fields)]

From: "J. Bruce Fields" <bfields@redhat.com>

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: 10b9d99a3dbb ("SUNRPC: Augment server-side rpcgss tracepoints")
Cc: stable@vger.kernel.org
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
---
 net/sunrpc/auth_gss/svcauth_gss.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/sunrpc/auth_gss/svcauth_gss.c b/net/sunrpc/auth_gss/svcauth_gss.c
index 7dba6a9c213a..b87565b64928 100644
--- a/net/sunrpc/auth_gss/svcauth_gss.c
+++ b/net/sunrpc/auth_gss/svcauth_gss.c
@@ -645,7 +645,7 @@ 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))
-- 
2.31.1