Re: [PATCH] net:sched fix array-index-out-of-bounds in taprio_change

在 2021/8/11 15:44, Eric Dumazet 写道:

On 8/11/21 7:10 AM, tcs.kernel@gmail.com wrote:

quoted

From: Haimin Zhang <redacted>

syzbot report an array-index-out-of-bounds in taprio_change
index 16 is out of range for type '__u16 [16]'
that's because mqprio->num_tc is lager than TC_MAX_QUEUE,so we check
the return value of netdev_set_num_tc.

Reported-by: <redacted>
Signed-off-by: Haimin Zhang <redacted>
---
  net/sched/sch_taprio.c | 4 +++-
  1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/net/sched/sch_taprio.c b/net/sched/sch_taprio.c
index 9c79374..1ab2fc9 100644
--- a/net/sched/sch_taprio.c
+++ b/net/sched/sch_taprio.c

@@ -1513,7 +1513,9 @@ static int taprio_change(struct Qdisc *sch, struct nlattr *opt,
  	taprio_set_picos_per_byte(dev, q);
  
  	if (mqprio) {
-		netdev_set_num_tc(dev, mqprio->num_tc);
+		err = netdev_set_num_tc(dev, mqprio->num_tc);
+		if (err)
+			goto free_sched;
  		for (i = 0; i < mqprio->num_tc; i++)
  			netdev_set_tc_queue(dev, i,
  					    mqprio->count[i],

When was the bug added ?

Hint: Please provide a Fixes: tag

taprio_parse_mqprio_opt() already checks :

/* Verify num_tc is not out of max range */
if (qopt->num_tc > TC_MAX_QUEUE) {
     NL_SET_ERR_MSG(extack, "Number of traffic classes is outside valid range");
     return -EINVAL;
}

So what is happening exactly ?

syzkaller reported this problem,the log shows mqprio->count[16] is accessed.
here is the log
https://syzkaller.appspot.com/bug?id=3a3677d4e7539ec5e671a81e32882ad40b5f7b64

the added check logic is hurtlessness,and netdev_set_num_tc does have a return value.