netdev - [PATCH net] sch_netem: fix issues in netem_change() vs get_dist

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Message-ID: <20230622181503.2327695-1-edumazet@google.com>
Date: Thu, 22 Jun 2023 18:15:03 +0000
From: Eric Dumazet <edumazet@...gle.com>
To: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>
Cc: netdev@...r.kernel.org, eric.dumazet@...il.com, 
	Eric Dumazet <edumazet@...gle.com>, syzbot <syzkaller@...glegroups.com>, 
	Stephen Hemminger <stephen@...workplumber.org>, Jamal Hadi Salim <jhs@...atatu.com>, 
	Simon Horman <simon.horman@...igine.com>
Subject: [PATCH net] sch_netem: fix issues in netem_change() vs get_dist_table()

In blamed commit, I missed that get_dist_table() was allocating
memory using GFP_KERNEL, and acquiring qdisc lock to perform
the swap of newly allocated table with current one.

In this patch, get_dist_table() is allocating memory and
copy user data before we acquire the qdisc lock.

Then we perform swap operations while being protected by the lock.

Note that after this patch netem_change() no longer can do partial changes.
If an error is returned, qdisc conf is left unchanged.

Fixes: 2174a08db80d ("sch_netem: acquire qdisc lock in netem_change()")
Reported-by: syzbot <syzkaller@...glegroups.com>
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Cc: Stephen Hemminger <stephen@...workplumber.org>
Cc: Jamal Hadi Salim <jhs@...atatu.com>
Cc: Simon Horman <simon.horman@...igine.com>
---
 net/sched/sch_netem.c | 59 ++++++++++++++++++-------------------------
 1 file changed, 25 insertions(+), 34 deletions(-)

diff --git a/net/sched/sch_netem.c b/net/sched/sch_netem.c
index e79be1b3e74da3c154f7ee23e16cc9e8da8f7106..b93ec2a3454ebceea559299f90533cbf1c0f7c26 100644
--- a/net/sched/sch_netem.c
+++ b/net/sched/sch_netem.c
@@ -773,12 +773,10 @@ static void dist_free(struct disttable *d)
  * signed 16 bit values.
  */
 
-static int get_dist_table(struct Qdisc *sch, struct disttable **tbl,
-			  const struct nlattr *attr)
+static int get_dist_table(struct disttable **tbl, const struct nlattr *attr)
 {
 	size_t n = nla_len(attr)/sizeof(__s16);
 	const __s16 *data = nla_data(attr);
-	spinlock_t *root_lock;
 	struct disttable *d;
 	int i;
 
@@ -793,13 +791,7 @@ static int get_dist_table(struct Qdisc *sch, struct disttable **tbl,
 	for (i = 0; i < n; i++)
 		d->table[i] = data[i];
 
-	root_lock = qdisc_root_sleeping_lock(sch);
-
-	spin_lock_bh(root_lock);
-	swap(*tbl, d);
-	spin_unlock_bh(root_lock);
-
-	dist_free(d);
+	*tbl = d;
 	return 0;
 }
 
@@ -956,6 +948,8 @@ static int netem_change(struct Qdisc *sch, struct nlattr *opt,
 {
 	struct netem_sched_data *q = qdisc_priv(sch);
 	struct nlattr *tb[TCA_NETEM_MAX + 1];
+	struct disttable *delay_dist = NULL;
+	struct disttable *slot_dist = NULL;
 	struct tc_netem_qopt *qopt;
 	struct clgstate old_clg;
 	int old_loss_model = CLG_RANDOM;
@@ -966,6 +960,18 @@ static int netem_change(struct Qdisc *sch, struct nlattr *opt,
 	if (ret < 0)
 		return ret;
 
+	if (tb[TCA_NETEM_DELAY_DIST]) {
+		ret = get_dist_table(&delay_dist, tb[TCA_NETEM_DELAY_DIST]);
+		if (ret)
+			goto table_free;
+	}
+
+	if (tb[TCA_NETEM_SLOT_DIST]) {
+		ret = get_dist_table(&slot_dist, tb[TCA_NETEM_SLOT_DIST]);
+		if (ret)
+			goto table_free;
+	}
+
 	sch_tree_lock(sch);
 	/* backup q->clg and q->loss_model */
 	old_clg = q->clg;
@@ -975,26 +981,17 @@ static int netem_change(struct Qdisc *sch, struct nlattr *opt,
 		ret = get_loss_clg(q, tb[TCA_NETEM_LOSS]);
 		if (ret) {
 			q->loss_model = old_loss_model;
+			q->clg = old_clg;
 			goto unlock;
 		}
 	} else {
 		q->loss_model = CLG_RANDOM;
 	}
 
-	if (tb[TCA_NETEM_DELAY_DIST]) {
-		ret = get_dist_table(sch, &q->delay_dist,
-				     tb[TCA_NETEM_DELAY_DIST]);
-		if (ret)
-			goto get_table_failure;
-	}
-
-	if (tb[TCA_NETEM_SLOT_DIST]) {
-		ret = get_dist_table(sch, &q->slot_dist,
-				     tb[TCA_NETEM_SLOT_DIST]);
-		if (ret)
-			goto get_table_failure;
-	}
-
+	if (delay_dist)
+		swap(q->delay_dist, delay_dist);
+	if (slot_dist)
+		swap(q->slot_dist, slot_dist);
 	sch->limit = qopt->limit;
 
 	q->latency = PSCHED_TICKS2NS(qopt->latency);
@@ -1044,17 +1041,11 @@ static int netem_change(struct Qdisc *sch, struct nlattr *opt,
 
 unlock:
 	sch_tree_unlock(sch);
-	return ret;
 
-get_table_failure:
-	/* recover clg and loss_model, in case of
-	 * q->clg and q->loss_model were modified
-	 * in get_loss_clg()
-	 */
-	q->clg = old_clg;
-	q->loss_model = old_loss_model;
-
-	goto unlock;
+table_free:
+	dist_free(delay_dist);
+	dist_free(slot_dist);
+	return ret;
 }
 
 static int netem_init(struct Qdisc *sch, struct nlattr *opt,
-- 
2.41.0.178.g377b9f9a00-goog