Patch "sch_netem: fix issues in netem_change() vs get_dist_table()" has been added to the 6.4-stable tree

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This is a note to let you know that I've just added the patch titled

    sch_netem: fix issues in netem_change() vs get_dist_table()

to the 6.4-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     sch_netem-fix-issues-in-netem_change-vs-get_dist_tab.patch
and it can be found in the queue-6.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit e8bb80cff7a75aa08ba4a5d03e71f67f94368c00
Author: Eric Dumazet <edumazet@xxxxxxxxxx>
Date:   Thu Jun 22 18:15:03 2023 +0000

    sch_netem: fix issues in netem_change() vs get_dist_table()
    
    [ Upstream commit 11b73313c12403f617b47752db0ab3deef201af7 ]
    
    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@xxxxxxxxxxxxxxxx>
    Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx>
    Cc: Stephen Hemminger <stephen@xxxxxxxxxxxxxxxxxx>
    Acked-by: Jamal Hadi Salim <jhs@xxxxxxxxxxxx>
    Reviewed-by: Simon Horman <simon.horman@xxxxxxxxxxxx>
    Link: https://lore.kernel.org/r/20230622181503.2327695-1-edumazet@xxxxxxxxxx
    Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/net/sched/sch_netem.c b/net/sched/sch_netem.c
index e79be1b3e74da..b93ec2a3454eb 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,



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