netdev - [PATCH iproute2-next] tc: mqprio: reject queues count/offset pair count higher than num

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Date:   Wed, 13 May 2020 21:47:17 +0200
From:   Maciej Fijalkowski <maciej.fijalkowski@...el.com>
To:     dsahern@...il.com, stephen@...workplumber.org
Cc:     netdev@...r.kernel.org, kiran.patil@...el.com,
        Maciej Fijalkowski <maciej.fijalkowski@...el.com>
Subject: [PATCH iproute2-next] tc: mqprio: reject queues count/offset pair count higher than num_tc

Provide a sanity check that will make sure whether queues count/offset
pair count will not exceed the actual number of TCs being created.

Example command that is invalid because there are 4 count/offset pairs
whereas num_tc is only 2.

 # tc qdisc add dev enp96s0f0 root mqprio num_tc 2 map 0 0 0 0 1 1 1 1
queues 4@0 4@4 4@8 4@12 hw 1 mode channel

Store the parsed count/offset pair count onto a dedicated variable that
will be compared against opt.num_tc after all of the command line
arguments were parsed. Bail out if this count is higher than opt.num_tc
and let user know about it.

Drivers were swallowing such commands as they were iterating over
count/offset pairs where num_tc was used as a delimiter, so this is not
a big deal, but better catch such misconfiguration at the command line
argument parsing level.

Signed-off-by: Maciej Fijalkowski <maciej.fijalkowski@...el.com>
---
 tc/q_mqprio.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/tc/q_mqprio.c b/tc/q_mqprio.c
index 0eb41308..f26ba8d7 100644
--- a/tc/q_mqprio.c
+++ b/tc/q_mqprio.c
@@ -48,6 +48,7 @@ static int mqprio_parse_opt(struct qdisc_util *qu, int argc,
 	__u64 max_rate64[TC_QOPT_MAX_QUEUE] = {0};
 	__u16 shaper = TC_MQPRIO_SHAPER_DCB;
 	__u16 mode = TC_MQPRIO_MODE_DCB;
+	int cnt_off_pairs = 0;
 	struct rtattr *tail;
 	__u32 flags = 0;

@@ -94,6 +95,7 @@ static int mqprio_parse_opt(struct qdisc_util *qu, int argc,
 				}
 				free(tmp);
 				idx++;
+				cnt_off_pairs++;
 			}
 		} else if (strcmp(*argv, "hw") == 0) {
 			NEXT_ARG();
@@ -173,6 +175,12 @@ static int mqprio_parse_opt(struct qdisc_util *qu, int argc,
 		argc--; argv++;
 	}

+	if (cnt_off_pairs > opt.num_tc) {
+		fprintf(stderr, "queues count/offset pair count %d can not be higher than given num_tc %d\n",
+			cnt_off_pairs, opt.num_tc);
+		return -1;
+	}
+
 	tail = NLMSG_TAIL(n);
 	addattr_l(n, 1024, TCA_OPTIONS, &opt, sizeof(opt));

-- 
2.20.1