Patch "sch_netem: acquire qdisc lock in netem_change()" has been added to the 4.19-stable tree

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

    sch_netem: acquire qdisc lock in netem_change()

to the 4.19-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-acquire-qdisc-lock-in-netem_change.patch
and it can be found in the queue-4.19 subdirectory.

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



commit 5331fa25e578272f015e3129a8b4b905eee15183
Author: Eric Dumazet <edumazet@xxxxxxxxxx>
Date:   Tue Jun 20 18:44:25 2023 +0000

    sch_netem: acquire qdisc lock in netem_change()
    
    [ Upstream commit 2174a08db80d1efeea382e25ac41c4e7511eb6d6 ]
    
    syzbot managed to trigger a divide error [1] in netem.
    
    It could happen if q->rate changes while netem_enqueue()
    is running, since q->rate is read twice.
    
    It turns out netem_change() always lacked proper synchronization.
    
    [1]
    divide error: 0000 [#1] SMP KASAN
    CPU: 1 PID: 7867 Comm: syz-executor.1 Not tainted 6.1.30-syzkaller #0
    Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/25/2023
    RIP: 0010:div64_u64 include/linux/math64.h:69 [inline]
    RIP: 0010:packet_time_ns net/sched/sch_netem.c:357 [inline]
    RIP: 0010:netem_enqueue+0x2067/0x36d0 net/sched/sch_netem.c:576
    Code: 89 e2 48 69 da 00 ca 9a 3b 42 80 3c 28 00 4c 8b a4 24 88 00 00 00 74 0d 4c 89 e7 e8 c3 4f 3b fd 48 8b 4c 24 18 48 89 d8 31 d2 <49> f7 34 24 49 01 c7 4c 8b 64 24 48 4d 01 f7 4c 89 e3 48 c1 eb 03
    RSP: 0018:ffffc9000dccea60 EFLAGS: 00010246
    RAX: 000001a442624200 RBX: 000001a442624200 RCX: ffff888108a4f000
    RDX: 0000000000000000 RSI: 000000000000070d RDI: 000000000000070d
    RBP: ffffc9000dcceb90 R08: ffffffff849c5e26 R09: fffffbfff10e1297
    R10: 0000000000000000 R11: dffffc0000000001 R12: ffff888108a4f358
    R13: dffffc0000000000 R14: 0000001a8cd9a7ec R15: 0000000000000000
    FS: 00007fa73fe18700(0000) GS:ffff8881f6b00000(0000) knlGS:0000000000000000
    CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
    CR2: 00007fa73fdf7718 CR3: 000000011d36e000 CR4: 0000000000350ee0
    Call Trace:
    <TASK>
    [<ffffffff84714385>] __dev_xmit_skb net/core/dev.c:3931 [inline]
    [<ffffffff84714385>] __dev_queue_xmit+0xcf5/0x3370 net/core/dev.c:4290
    [<ffffffff84d22df2>] dev_queue_xmit include/linux/netdevice.h:3030 [inline]
    [<ffffffff84d22df2>] neigh_hh_output include/net/neighbour.h:531 [inline]
    [<ffffffff84d22df2>] neigh_output include/net/neighbour.h:545 [inline]
    [<ffffffff84d22df2>] ip_finish_output2+0xb92/0x10d0 net/ipv4/ip_output.c:235
    [<ffffffff84d21e63>] __ip_finish_output+0xc3/0x2b0
    [<ffffffff84d10a81>] ip_finish_output+0x31/0x2a0 net/ipv4/ip_output.c:323
    [<ffffffff84d10f14>] NF_HOOK_COND include/linux/netfilter.h:298 [inline]
    [<ffffffff84d10f14>] ip_output+0x224/0x2a0 net/ipv4/ip_output.c:437
    [<ffffffff84d123b5>] dst_output include/net/dst.h:444 [inline]
    [<ffffffff84d123b5>] ip_local_out net/ipv4/ip_output.c:127 [inline]
    [<ffffffff84d123b5>] __ip_queue_xmit+0x1425/0x2000 net/ipv4/ip_output.c:542
    [<ffffffff84d12fdc>] ip_queue_xmit+0x4c/0x70 net/ipv4/ip_output.c:556
    
    Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
    Reported-by: syzbot <syzkaller@xxxxxxxxxxxxxxxx>
    Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx>
    Cc: Stephen Hemminger <stephen@xxxxxxxxxxxxxxxxxx>
    Cc: Jamal Hadi Salim <jhs@xxxxxxxxxxxx>
    Cc: Cong Wang <xiyou.wangcong@xxxxxxxxx>
    Cc: Jiri Pirko <jiri@xxxxxxxxxxx>
    Reviewed-by: Jamal Hadi Salim <jhs@xxxxxxxxxxxx>
    Reviewed-by: Simon Horman <simon.horman@xxxxxxxxxxxx>
    Link: https://lore.kernel.org/r/20230620184425.1179809-1-edumazet@xxxxxxxxxx
    Signed-off-by: Paolo Abeni <pabeni@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/net/sched/sch_netem.c b/net/sched/sch_netem.c
index 31793af1a77bd..93548b9e07cf1 100644
--- a/net/sched/sch_netem.c
+++ b/net/sched/sch_netem.c
@@ -943,6 +943,7 @@ static int netem_change(struct Qdisc *sch, struct nlattr *opt,
 	if (ret < 0)
 		return ret;
 
+	sch_tree_lock(sch);
 	/* backup q->clg and q->loss_model */
 	old_clg = q->clg;
 	old_loss_model = q->loss_model;
@@ -951,7 +952,7 @@ 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;
-			return ret;
+			goto unlock;
 		}
 	} else {
 		q->loss_model = CLG_RANDOM;
@@ -1018,6 +1019,8 @@ static int netem_change(struct Qdisc *sch, struct nlattr *opt,
 	/* capping jitter to the range acceptable by tabledist() */
 	q->jitter = min_t(s64, abs(q->jitter), INT_MAX);
 
+unlock:
+	sch_tree_unlock(sch);
 	return ret;
 
 get_table_failure:
@@ -1027,7 +1030,8 @@ static int netem_change(struct Qdisc *sch, struct nlattr *opt,
 	 */
 	q->clg = old_clg;
 	q->loss_model = old_loss_model;
-	return ret;
+
+	goto unlock;
 }
 
 static int netem_init(struct Qdisc *sch, struct nlattr *opt,



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