[PATCH 4.9.y] net: sched: prevent UAF on tc_ctl_tfilter when temporarily dropping rtnl_lock

[PATCH 4.9.y] net: sched: prevent UAF on tc_ctl_tfilter when temporarily dropping rtnl_lock

[Thadeu Lima de Souza Cascardo]

When dropping the rtnl_lock for looking up for a module, the device may be
removed, releasing the qdisc and class memory. Right after trying to load
the module, cl_ops->put is called, leading to a potential use-after-free.

Though commit e368fdb61d8e ("net: sched: use Qdisc rcu API instead of
relying on rtnl lock") fixes this, it involves a lot of refactoring of the
net/sched/ code, complicating its backport.

This fix calls cl_ops->put before dropping rtnl_lock as it will be called
either way, and zeroes it out so it won't be called again on the exit path.

This has been shown to stop the following KASAN report with the reproducer:

[  256.609111] ==================================================================
[  256.609585] BUG: KASAN: use-after-free in cbq_put+0x20/0xd0 at addr ffff880021daaba0
[  256.610078] Read of size 4 by task total_cbq/11184
[  256.610380] CPU: 0 PID: 11184 Comm: total_cbq Not tainted 4.9.311 #78
[  256.610778]  ffff8800215875a8 ffffffff96e18735 ffff880024803080 ffff880021daaa80
[  256.611274]  ffff8800215875d0 ffffffff96334841 ffffed00043b5574 ffffed00043b5574
[  256.611768]  ffff880024803080 ffff880021587658 ffffffff96334af8 0000000000000000
[  256.612186] Call Trace:
[  256.612344]  [<ffffffff96e18735>] dump_stack+0x6d/0x8b
[  256.612632]  [<ffffffff96334841>] kasan_object_err+0x21/0x70
[  256.612973]  [<ffffffff96334af8>] kasan_report.part.1+0x218/0x4f0
[  256.613349]  [<ffffffff96c5a2e0>] ? cbq_put+0x20/0xd0
[  256.613634]  [<ffffffff96333cd6>] ? kasan_unpoison_shadow+0x36/0x50
[  256.613993]  [<ffffffff96335105>] kasan_report+0x25/0x30
[  256.614288]  [<ffffffff96333701>] __asan_load4+0x61/0x80
[  256.614580]  [<ffffffff96c5a2e0>] cbq_put+0x20/0xd0
[  256.614862]  [<ffffffff96c53184>] tc_ctl_tfilter+0x4f4/0xb80
[  256.615151]  [<ffffffff96c52c90>] ? tfilter_notify+0x140/0x140
[  256.615478]  [<ffffffff960056ef>] ? do_syscall_64+0xef/0x190
[  256.615799]  [<ffffffff96e28a8e>] ? entry_SYSCALL_64_after_swapgs+0x58/0xc6
[  256.616190]  [<ffffffff96bce3f6>] ? sock_sendmsg+0x76/0x80
[  256.616484]  [<ffffffff96bce53f>] ? sock_write_iter+0x13f/0x1f0
[  256.616833]  [<ffffffff96367b02>] ? __vfs_write+0x262/0x3c0
[  256.617152]  [<ffffffff96369dc9>] ? vfs_write+0xf9/0x260
[  256.617451]  [<ffffffff9636c009>] ? SyS_write+0xc9/0x1b0
[  256.617754]  [<ffffffff960decda>] ? ns_capable_common+0x5a/0xa0
[  256.618067]  [<ffffffff960ded33>] ? ns_capable+0x13/0x20
[  256.618334]  [<ffffffff96c9125d>] ? __netlink_ns_capable+0x6d/0x80
[  256.618666]  [<ffffffff96c2750f>] rtnetlink_rcv_msg+0x1af/0x410
[  256.618969]  [<ffffffff96c90d6b>] ? netlink_compare+0x5b/0x70
[  256.619295]  [<ffffffff96c27360>] ? rtnl_newlink+0xc60/0xc60
[  256.619587]  [<ffffffff96c94214>] ? __netlink_lookup+0x1a4/0x240
[  256.619885]  [<ffffffff96c94070>] ? netlink_broadcast+0x20/0x20
[  256.620179]  [<ffffffff96c97815>] netlink_rcv_skb+0x155/0x190
[  256.620463]  [<ffffffff96c27360>] ? rtnl_newlink+0xc60/0xc60
[  256.620748]  [<ffffffff96c1e758>] rtnetlink_rcv+0x28/0x30
[  256.621015]  [<ffffffff96c96d11>] netlink_unicast+0x2f1/0x3b0
[  256.621354]  [<ffffffff96c96a20>] ? netlink_attachskb+0x340/0x340
[  256.621765]  [<ffffffff96c9733e>] netlink_sendmsg+0x56e/0x6f0
[  256.622181]  [<ffffffff96c96dd0>] ? netlink_unicast+0x3b0/0x3b0
[  256.622578]  [<ffffffff96c96dd0>] ? netlink_unicast+0x3b0/0x3b0
[  256.622893]  [<ffffffff96bce3f6>] sock_sendmsg+0x76/0x80
[  256.623157]  [<ffffffff96bce53f>] sock_write_iter+0x13f/0x1f0
[  256.623440]  [<ffffffff96bce400>] ? sock_sendmsg+0x80/0x80
[  256.623729]  [<ffffffff966a8032>] ? iov_iter_init+0x82/0xc0
[  256.624006]  [<ffffffff96367b02>] __vfs_write+0x262/0x3c0
[  256.624274]  [<ffffffff963678a0>] ? default_llseek+0x120/0x120
[  256.624566]  [<ffffffff965e8c02>] ? common_file_perm+0x92/0x170
[  256.624925]  [<ffffffff96369a58>] ? rw_verify_area+0x78/0x140
[  256.625277]  [<ffffffff96369dc9>] vfs_write+0xf9/0x260
[  256.625593]  [<ffffffff9636c009>] SyS_write+0xc9/0x1b0
[  256.625891]  [<ffffffff9636bf40>] ? SyS_read+0x1b0/0x1b0
[  256.626154]  [<ffffffff9636bf40>] ? SyS_read+0x1b0/0x1b0
[  256.626422]  [<ffffffff960056ef>] do_syscall_64+0xef/0x190
[  256.626697]  [<ffffffff96e28a8e>] entry_SYSCALL_64_after_swapgs+0x58/0xc6
[  256.627033] Object at ffff880021daaa80, in cache kmalloc-512 size: 512
[  256.627415] Allocated:
[  256.627563] PID = 164
[  256.627711]  save_stack_trace+0x1b/0x20
[  256.627947]  save_stack+0x46/0xd0
[  256.628151]  kasan_kmalloc+0xad/0xe0
[  256.628362]  kmem_cache_alloc_trace+0xe8/0x1e0
[  256.628637]  cbq_change_class+0x8b6/0xde0
[  256.628896]  tc_ctl_tclass+0x56a/0x5b0
[  256.629129]  rtnetlink_rcv_msg+0x1af/0x410
[  256.629380]  netlink_rcv_skb+0x155/0x190
[  256.629621]  rtnetlink_rcv+0x28/0x30
[  256.629840]  netlink_unicast+0x2f1/0x3b0
[  256.630066]  netlink_sendmsg+0x56e/0x6f0
[  256.630263]  sock_sendmsg+0x76/0x80
[  256.630456]  sock_write_iter+0x13f/0x1f0
[  256.630698]  __vfs_write+0x262/0x3c0
[  256.630918]  vfs_write+0xf9/0x260
[  256.631123]  SyS_write+0xc9/0x1b0
[  256.631327]  do_syscall_64+0xef/0x190
[  256.631553]  entry_SYSCALL_64_after_swapgs+0x58/0xc6
[  256.631827] Freed:
[  256.631931] PID = 164
[  256.632048]  save_stack_trace+0x1b/0x20
[  256.632241]  save_stack+0x46/0xd0
[  256.632408]  kasan_slab_free+0x71/0xb0
[  256.632597]  kfree+0x8c/0x1a0
[  256.632751]  cbq_destroy_class+0x85/0xa0
[  256.632948]  cbq_destroy+0xfa/0x120
[  256.633125]  qdisc_destroy+0xa1/0x140
[  256.633309]  dev_shutdown+0x12d/0x190
[  256.633497]  rollback_registered_many+0x43c/0x5b0
[  256.633753]  unregister_netdevice_many+0x2c/0x130
[  256.634041]  rtnl_delete_link+0xb3/0x100
[  256.634283]  rtnl_dellink+0x19c/0x360
[  256.634509]  rtnetlink_rcv_msg+0x1af/0x410
[  256.634760]  netlink_rcv_skb+0x155/0x190
[  256.635001]  rtnetlink_rcv+0x28/0x30
[  256.635221]  netlink_unicast+0x2f1/0x3b0
[  256.635463]  netlink_sendmsg+0x56e/0x6f0
[  256.635700]  sock_sendmsg+0x76/0x80
[  256.635915]  sock_write_iter+0x13f/0x1f0
[  256.636156]  __vfs_write+0x262/0x3c0
[  256.636376]  vfs_write+0xf9/0x260
[  256.636580]  SyS_write+0xc9/0x1b0
[  256.636787]  do_syscall_64+0xef/0x190
[  256.637013]  entry_SYSCALL_64_after_swapgs+0x58/0xc6
[  256.637316] Memory state around the buggy address:
[  256.637610]  ffff880021daaa80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
[  256.638047]  ffff880021daab00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
[  256.638487] >ffff880021daab80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
[  256.638924]                                ^
[  256.639186]  ffff880021daac00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
[  256.639624]  ffff880021daac80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc

Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
---
 net/sched/cls_api.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/net/sched/cls_api.c b/net/sched/cls_api.c
index c1a4b5d30814..330a2c9d1907 100644
--- a/net/sched/cls_api.c
+++ b/net/sched/cls_api.c
@@ -268,10 +268,13 @@ static int tc_ctl_tfilter(struct sk_buff *skb, struct nlmsghdr *n)
 		err = -ENOENT;
 		tp_ops = tcf_proto_lookup_ops(tca[TCA_KIND]);
 		if (tp_ops == NULL) {
-#ifdef CONFIG_MODULES
 			struct nlattr *kind = tca[TCA_KIND];
 			char name[IFNAMSIZ];
 
+			if (cl)
+				cops->put(q, cl);
+			cl = 0;
+#ifdef CONFIG_MODULES
 			if (kind != NULL &&
 			    nla_strlcpy(name, kind, IFNAMSIZ) < IFNAMSIZ) {
 				rtnl_unlock();
-- 
2.32.0

Re: [PATCH 4.9.y] net: sched: prevent UAF on tc_ctl_tfilter when temporarily dropping rtnl_lock

[Greg KH]

On Mon, May 02, 2022 at 05:49:24PM -0300, Thadeu Lima de Souza Cascardo wrote:
> When dropping the rtnl_lock for looking up for a module, the device may be
> removed, releasing the qdisc and class memory. Right after trying to load
> the module, cl_ops->put is called, leading to a potential use-after-free.
> 
> Though commit e368fdb61d8e ("net: sched: use Qdisc rcu API instead of
> relying on rtnl lock") fixes this, it involves a lot of refactoring of the
> net/sched/ code, complicating its backport.

What about 4.14.y?  We can not take a commit for 4.9.y with it also
being broken in 4.14.y, and yet fixed in 4.19.y, right?  Anyone who
updates from 4.9 to 4.14 will have a regression.

thanks,

greg k-h

Re: [PATCH 4.9.y] net: sched: prevent UAF on tc_ctl_tfilter when temporarily dropping rtnl_lock

[Thadeu Lima de Souza Cascardo]

On Tue, May 03, 2022 at 03:49:15PM +0200, Greg KH wrote:
> On Mon, May 02, 2022 at 05:49:24PM -0300, Thadeu Lima de Souza Cascardo wrote:
> > When dropping the rtnl_lock for looking up for a module, the device may be
> > removed, releasing the qdisc and class memory. Right after trying to load
> > the module, cl_ops->put is called, leading to a potential use-after-free.
> > 
> > Though commit e368fdb61d8e ("net: sched: use Qdisc rcu API instead of
> > relying on rtnl lock") fixes this, it involves a lot of refactoring of the
> > net/sched/ code, complicating its backport.
> 
> What about 4.14.y?  We can not take a commit for 4.9.y with it also
> being broken in 4.14.y, and yet fixed in 4.19.y, right?  Anyone who
> updates from 4.9 to 4.14 will have a regression.
> 
> thanks,
> 
> greg k-h

4.14.y does not call cl_ops->put (the get/put and class refcount has been done
with on 4.14.y). However, on the error path after the lock has been dropped,
tcf_chain_put is called. But it does not touch the qdisc, but only the chain
and block objects, which cannot be released on a race condition, as far as I
was able to investigate.

Cascardo.

Re: [PATCH 4.9.y] net: sched: prevent UAF on tc_ctl_tfilter when temporarily dropping rtnl_lock

[Greg KH]

On Tue, May 03, 2022 at 11:24:01AM -0300, Thadeu Lima de Souza Cascardo wrote:
> On Tue, May 03, 2022 at 03:49:15PM +0200, Greg KH wrote:
> > On Mon, May 02, 2022 at 05:49:24PM -0300, Thadeu Lima de Souza Cascardo wrote:
> > > When dropping the rtnl_lock for looking up for a module, the device may be
> > > removed, releasing the qdisc and class memory. Right after trying to load
> > > the module, cl_ops->put is called, leading to a potential use-after-free.
> > > 
> > > Though commit e368fdb61d8e ("net: sched: use Qdisc rcu API instead of
> > > relying on rtnl lock") fixes this, it involves a lot of refactoring of the
> > > net/sched/ code, complicating its backport.
> > 
> > What about 4.14.y?  We can not take a commit for 4.9.y with it also
> > being broken in 4.14.y, and yet fixed in 4.19.y, right?  Anyone who
> > updates from 4.9 to 4.14 will have a regression.
> > 
> > thanks,
> > 
> > greg k-h
> 
> 4.14.y does not call cl_ops->put (the get/put and class refcount has been done
> with on 4.14.y). However, on the error path after the lock has been dropped,
> tcf_chain_put is called. But it does not touch the qdisc, but only the chain
> and block objects, which cannot be released on a race condition, as far as I
> was able to investigate.

So what changed between 4.9 and 4.14 that requires this out-of-tree
change to 4.9 for the issue?  Shouldn't we backport that change instead
of this custom one?

thanks,

greg k-h

Re: [PATCH 4.9.y] net: sched: prevent UAF on tc_ctl_tfilter when temporarily dropping rtnl_lock

[Thadeu Lima de Souza Cascardo]

On Tue, May 03, 2022 at 04:27:20PM +0200, Greg KH wrote:
> On Tue, May 03, 2022 at 11:24:01AM -0300, Thadeu Lima de Souza Cascardo wrote:
> > On Tue, May 03, 2022 at 03:49:15PM +0200, Greg KH wrote:
> > > On Mon, May 02, 2022 at 05:49:24PM -0300, Thadeu Lima de Souza Cascardo wrote:
> > > > When dropping the rtnl_lock for looking up for a module, the device may be
> > > > removed, releasing the qdisc and class memory. Right after trying to load
> > > > the module, cl_ops->put is called, leading to a potential use-after-free.
> > > > 
> > > > Though commit e368fdb61d8e ("net: sched: use Qdisc rcu API instead of
> > > > relying on rtnl lock") fixes this, it involves a lot of refactoring of the
> > > > net/sched/ code, complicating its backport.
> > > 
> > > What about 4.14.y?  We can not take a commit for 4.9.y with it also
> > > being broken in 4.14.y, and yet fixed in 4.19.y, right?  Anyone who
> > > updates from 4.9 to 4.14 will have a regression.
> > > 
> > > thanks,
> > > 
> > > greg k-h
> > 
> > 4.14.y does not call cl_ops->put (the get/put and class refcount has been done
> > with on 4.14.y). However, on the error path after the lock has been dropped,
> > tcf_chain_put is called. But it does not touch the qdisc, but only the chain
> > and block objects, which cannot be released on a race condition, as far as I
> > was able to investigate.
> 
> So what changed between 4.9 and 4.14 that requires this out-of-tree
> change to 4.9 for the issue?  Shouldn't we backport that change instead
> of this custom one?
> 
> thanks,
> 
> greg k-h

143976ce992f ("net_sched: remove tc class reference counting") removed the call
to cops->put as that reference counting was removed and the get call was
replaced by find.

Backporting it is an alternative fix, but there are more chances of breaking
something else, as it is not a trivial cherry-pick.

Cascardo.

Re: [PATCH 4.9.y] net: sched: prevent UAF on tc_ctl_tfilter when temporarily dropping rtnl_lock

[Greg KH]

On Mon, May 02, 2022 at 05:49:24PM -0300, Thadeu Lima de Souza Cascardo wrote:
> When dropping the rtnl_lock for looking up for a module, the device may be
> removed, releasing the qdisc and class memory. Right after trying to load
> the module, cl_ops->put is called, leading to a potential use-after-free.
> 
> Though commit e368fdb61d8e ("net: sched: use Qdisc rcu API instead of
> relying on rtnl lock") fixes this, it involves a lot of refactoring of the
> net/sched/ code, complicating its backport.
> 
> This fix calls cl_ops->put before dropping rtnl_lock as it will be called
> either way, and zeroes it out so it won't be called again on the exit path.
> 
> This has been shown to stop the following KASAN report with the reproducer:
> 
> [  256.609111] ==================================================================
> [  256.609585] BUG: KASAN: use-after-free in cbq_put+0x20/0xd0 at addr ffff880021daaba0
> [  256.610078] Read of size 4 by task total_cbq/11184
> [  256.610380] CPU: 0 PID: 11184 Comm: total_cbq Not tainted 4.9.311 #78
> [  256.610778]  ffff8800215875a8 ffffffff96e18735 ffff880024803080 ffff880021daaa80
> [  256.611274]  ffff8800215875d0 ffffffff96334841 ffffed00043b5574 ffffed00043b5574
> [  256.611768]  ffff880024803080 ffff880021587658 ffffffff96334af8 0000000000000000
> [  256.612186] Call Trace:
> [  256.612344]  [<ffffffff96e18735>] dump_stack+0x6d/0x8b
> [  256.612632]  [<ffffffff96334841>] kasan_object_err+0x21/0x70
> [  256.612973]  [<ffffffff96334af8>] kasan_report.part.1+0x218/0x4f0
> [  256.613349]  [<ffffffff96c5a2e0>] ? cbq_put+0x20/0xd0
> [  256.613634]  [<ffffffff96333cd6>] ? kasan_unpoison_shadow+0x36/0x50
> [  256.613993]  [<ffffffff96335105>] kasan_report+0x25/0x30
> [  256.614288]  [<ffffffff96333701>] __asan_load4+0x61/0x80
> [  256.614580]  [<ffffffff96c5a2e0>] cbq_put+0x20/0xd0
> [  256.614862]  [<ffffffff96c53184>] tc_ctl_tfilter+0x4f4/0xb80
> [  256.615151]  [<ffffffff96c52c90>] ? tfilter_notify+0x140/0x140
> [  256.615478]  [<ffffffff960056ef>] ? do_syscall_64+0xef/0x190
> [  256.615799]  [<ffffffff96e28a8e>] ? entry_SYSCALL_64_after_swapgs+0x58/0xc6
> [  256.616190]  [<ffffffff96bce3f6>] ? sock_sendmsg+0x76/0x80
> [  256.616484]  [<ffffffff96bce53f>] ? sock_write_iter+0x13f/0x1f0
> [  256.616833]  [<ffffffff96367b02>] ? __vfs_write+0x262/0x3c0
> [  256.617152]  [<ffffffff96369dc9>] ? vfs_write+0xf9/0x260
> [  256.617451]  [<ffffffff9636c009>] ? SyS_write+0xc9/0x1b0
> [  256.617754]  [<ffffffff960decda>] ? ns_capable_common+0x5a/0xa0
> [  256.618067]  [<ffffffff960ded33>] ? ns_capable+0x13/0x20
> [  256.618334]  [<ffffffff96c9125d>] ? __netlink_ns_capable+0x6d/0x80
> [  256.618666]  [<ffffffff96c2750f>] rtnetlink_rcv_msg+0x1af/0x410
> [  256.618969]  [<ffffffff96c90d6b>] ? netlink_compare+0x5b/0x70
> [  256.619295]  [<ffffffff96c27360>] ? rtnl_newlink+0xc60/0xc60
> [  256.619587]  [<ffffffff96c94214>] ? __netlink_lookup+0x1a4/0x240
> [  256.619885]  [<ffffffff96c94070>] ? netlink_broadcast+0x20/0x20
> [  256.620179]  [<ffffffff96c97815>] netlink_rcv_skb+0x155/0x190
> [  256.620463]  [<ffffffff96c27360>] ? rtnl_newlink+0xc60/0xc60
> [  256.620748]  [<ffffffff96c1e758>] rtnetlink_rcv+0x28/0x30
> [  256.621015]  [<ffffffff96c96d11>] netlink_unicast+0x2f1/0x3b0
> [  256.621354]  [<ffffffff96c96a20>] ? netlink_attachskb+0x340/0x340
> [  256.621765]  [<ffffffff96c9733e>] netlink_sendmsg+0x56e/0x6f0
> [  256.622181]  [<ffffffff96c96dd0>] ? netlink_unicast+0x3b0/0x3b0
> [  256.622578]  [<ffffffff96c96dd0>] ? netlink_unicast+0x3b0/0x3b0
> [  256.622893]  [<ffffffff96bce3f6>] sock_sendmsg+0x76/0x80
> [  256.623157]  [<ffffffff96bce53f>] sock_write_iter+0x13f/0x1f0
> [  256.623440]  [<ffffffff96bce400>] ? sock_sendmsg+0x80/0x80
> [  256.623729]  [<ffffffff966a8032>] ? iov_iter_init+0x82/0xc0
> [  256.624006]  [<ffffffff96367b02>] __vfs_write+0x262/0x3c0
> [  256.624274]  [<ffffffff963678a0>] ? default_llseek+0x120/0x120
> [  256.624566]  [<ffffffff965e8c02>] ? common_file_perm+0x92/0x170
> [  256.624925]  [<ffffffff96369a58>] ? rw_verify_area+0x78/0x140
> [  256.625277]  [<ffffffff96369dc9>] vfs_write+0xf9/0x260
> [  256.625593]  [<ffffffff9636c009>] SyS_write+0xc9/0x1b0
> [  256.625891]  [<ffffffff9636bf40>] ? SyS_read+0x1b0/0x1b0
> [  256.626154]  [<ffffffff9636bf40>] ? SyS_read+0x1b0/0x1b0
> [  256.626422]  [<ffffffff960056ef>] do_syscall_64+0xef/0x190
> [  256.626697]  [<ffffffff96e28a8e>] entry_SYSCALL_64_after_swapgs+0x58/0xc6
> [  256.627033] Object at ffff880021daaa80, in cache kmalloc-512 size: 512
> [  256.627415] Allocated:
> [  256.627563] PID = 164
> [  256.627711]  save_stack_trace+0x1b/0x20
> [  256.627947]  save_stack+0x46/0xd0
> [  256.628151]  kasan_kmalloc+0xad/0xe0
> [  256.628362]  kmem_cache_alloc_trace+0xe8/0x1e0
> [  256.628637]  cbq_change_class+0x8b6/0xde0
> [  256.628896]  tc_ctl_tclass+0x56a/0x5b0
> [  256.629129]  rtnetlink_rcv_msg+0x1af/0x410
> [  256.629380]  netlink_rcv_skb+0x155/0x190
> [  256.629621]  rtnetlink_rcv+0x28/0x30
> [  256.629840]  netlink_unicast+0x2f1/0x3b0
> [  256.630066]  netlink_sendmsg+0x56e/0x6f0
> [  256.630263]  sock_sendmsg+0x76/0x80
> [  256.630456]  sock_write_iter+0x13f/0x1f0
> [  256.630698]  __vfs_write+0x262/0x3c0
> [  256.630918]  vfs_write+0xf9/0x260
> [  256.631123]  SyS_write+0xc9/0x1b0
> [  256.631327]  do_syscall_64+0xef/0x190
> [  256.631553]  entry_SYSCALL_64_after_swapgs+0x58/0xc6
> [  256.631827] Freed:
> [  256.631931] PID = 164
> [  256.632048]  save_stack_trace+0x1b/0x20
> [  256.632241]  save_stack+0x46/0xd0
> [  256.632408]  kasan_slab_free+0x71/0xb0
> [  256.632597]  kfree+0x8c/0x1a0
> [  256.632751]  cbq_destroy_class+0x85/0xa0
> [  256.632948]  cbq_destroy+0xfa/0x120
> [  256.633125]  qdisc_destroy+0xa1/0x140
> [  256.633309]  dev_shutdown+0x12d/0x190
> [  256.633497]  rollback_registered_many+0x43c/0x5b0
> [  256.633753]  unregister_netdevice_many+0x2c/0x130
> [  256.634041]  rtnl_delete_link+0xb3/0x100
> [  256.634283]  rtnl_dellink+0x19c/0x360
> [  256.634509]  rtnetlink_rcv_msg+0x1af/0x410
> [  256.634760]  netlink_rcv_skb+0x155/0x190
> [  256.635001]  rtnetlink_rcv+0x28/0x30
> [  256.635221]  netlink_unicast+0x2f1/0x3b0
> [  256.635463]  netlink_sendmsg+0x56e/0x6f0
> [  256.635700]  sock_sendmsg+0x76/0x80
> [  256.635915]  sock_write_iter+0x13f/0x1f0
> [  256.636156]  __vfs_write+0x262/0x3c0
> [  256.636376]  vfs_write+0xf9/0x260
> [  256.636580]  SyS_write+0xc9/0x1b0
> [  256.636787]  do_syscall_64+0xef/0x190
> [  256.637013]  entry_SYSCALL_64_after_swapgs+0x58/0xc6
> [  256.637316] Memory state around the buggy address:
> [  256.637610]  ffff880021daaa80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> [  256.638047]  ffff880021daab00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> [  256.638487] >ffff880021daab80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> [  256.638924]                                ^
> [  256.639186]  ffff880021daac00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> [  256.639624]  ffff880021daac80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> 
> Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
> ---
>  net/sched/cls_api.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/net/sched/cls_api.c b/net/sched/cls_api.c
> index c1a4b5d30814..330a2c9d1907 100644
> --- a/net/sched/cls_api.c
> +++ b/net/sched/cls_api.c
> @@ -268,10 +268,13 @@ static int tc_ctl_tfilter(struct sk_buff *skb, struct nlmsghdr *n)
>  		err = -ENOENT;
>  		tp_ops = tcf_proto_lookup_ops(tca[TCA_KIND]);
>  		if (tp_ops == NULL) {
> -#ifdef CONFIG_MODULES
>  			struct nlattr *kind = tca[TCA_KIND];
>  			char name[IFNAMSIZ];
>  
> +			if (cl)
> +				cops->put(q, cl);
> +			cl = 0;
> +#ifdef CONFIG_MODULES
>  			if (kind != NULL &&
>  			    nla_strlcpy(name, kind, IFNAMSIZ) < IFNAMSIZ) {
>  				rtnl_unlock();
> -- 
> 2.32.0
> 

Now queued up, thanks.

greg k-h