[PATCH net-next] ip6_tunnel: sit: proper dev_{hold|put} in ndo_[un]init methods

[PATCH net-next] ip6_tunnel: sit: proper dev_{hold|put} in ndo_[un]init methods

[Eric Dumazet]

From: Eric Dumazet <edumazet@google.com>

Same reasons than for the previous commits :
6289a98f0817 ("sit: proper dev_{hold|put} in ndo_[un]init methods")
40cb881b5aaa ("ip6_vti: proper dev_{hold|put} in ndo_[un]init methods")
7f700334be9a ("ip6_gre: proper dev_{hold|put} in ndo_[un]init methods")

After adopting CONFIG_PCPU_DEV_REFCNT=n option, syzbot was able to trigger
a warning [1]

Issue here is that:

- all dev_put() should be paired with a corresponding prior dev_hold().

- A driver doing a dev_put() in its ndo_uninit() MUST also
  do a dev_hold() in its ndo_init(), only when ndo_init()
  is returning 0.

Otherwise, register_netdevice() would call ndo_uninit()
in its error path and release a refcount too soon.

[1]
WARNING: CPU: 1 PID: 21059 at lib/refcount.c:31 refcount_warn_saturate+0xbf/0x1e0 lib/refcount.c:31
Modules linked in:
CPU: 1 PID: 21059 Comm: syz-executor.4 Not tainted 5.12.0-rc4-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:refcount_warn_saturate+0xbf/0x1e0 lib/refcount.c:31
Code: 1d 6a 5a e8 09 31 ff 89 de e8 8d 1a ab fd 84 db 75 e0 e8 d4 13 ab fd 48 c7 c7 a0 e1 c1 89 c6 05 4a 5a e8 09 01 e8 2e 36 fb 04 <0f> 0b eb c4 e8 b8 13 ab fd 0f b6 1d 39 5a e8 09 31 ff 89 de e8 58
RSP: 0018:ffffc900025aefe8 EFLAGS: 00010282
RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
RDX: 0000000000040000 RSI: ffffffff815c51f5 RDI: fffff520004b5def
RBP: 0000000000000004 R08: 0000000000000000 R09: 0000000000000000
R10: ffffffff815bdf8e R11: 0000000000000000 R12: ffff888023488568
R13: ffff8880254e9000 R14: 00000000dfd82cfd R15: ffff88802ee2d7c0
FS:  00007f13bc590700(0000) GS:ffff8880b9c00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f0943e74000 CR3: 0000000025273000 CR4: 00000000001506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 __refcount_dec include/linux/refcount.h:344 [inline]
 refcount_dec include/linux/refcount.h:359 [inline]
 dev_put include/linux/netdevice.h:4135 [inline]
 ip6_tnl_dev_uninit+0x370/0x3d0 net/ipv6/ip6_tunnel.c:387
 register_netdevice+0xadf/0x1500 net/core/dev.c:10308
 ip6_tnl_create2+0x1b5/0x400 net/ipv6/ip6_tunnel.c:263
 ip6_tnl_newlink+0x312/0x580 net/ipv6/ip6_tunnel.c:2052
 __rtnl_newlink+0x1062/0x1710 net/core/rtnetlink.c:3443
 rtnl_newlink+0x64/0xa0 net/core/rtnetlink.c:3491
 rtnetlink_rcv_msg+0x44e/0xad0 net/core/rtnetlink.c:5553
 netlink_rcv_skb+0x153/0x420 net/netlink/af_netlink.c:2502
 netlink_unicast_kernel net/netlink/af_netlink.c:1312 [inline]
 netlink_unicast+0x533/0x7d0 net/netlink/af_netlink.c:1338
 netlink_sendmsg+0x856/0xd90 net/netlink/af_netlink.c:1927
 sock_sendmsg_nosec net/socket.c:654 [inline]
 sock_sendmsg+0xcf/0x120 net/socket.c:674
 ____sys_sendmsg+0x6e8/0x810 net/socket.c:2350
 ___sys_sendmsg+0xf3/0x170 net/socket.c:2404
 __sys_sendmsg+0xe5/0x1b0 net/socket.c:2433
 do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xae

Fixes: 919067cc845f ("net: add CONFIG_PCPU_DEV_REFCNT")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: syzbot <syzkaller@googlegroups.com>
---
 net/ipv6/ip6_tunnel.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/ipv6/ip6_tunnel.c b/net/ipv6/ip6_tunnel.c
index cd78f5b2cd75e20a79fd6c4cbfafd548204c2b7c..67ee9d58ec5efcc81e8b27406bd4f57a0caea70b 100644
--- a/net/ipv6/ip6_tunnel.c
+++ b/net/ipv6/ip6_tunnel.c
@@ -266,7 +266,6 @@ static int ip6_tnl_create2(struct net_device *dev)
 
 	strcpy(t->parms.name, dev->name);
 
-	dev_hold(dev);
 	ip6_tnl_link(ip6n, t);
 	return 0;
 
@@ -1882,6 +1881,7 @@ ip6_tnl_dev_init_gen(struct net_device *dev)
 	dev->min_mtu = ETH_MIN_MTU;
 	dev->max_mtu = IP6_MAX_MTU - dev->hard_header_len;
 
+	dev_hold(dev);
 	return 0;
 
 destroy_dst:
-- 
2.31.0.291.g576ba9dcdaf-goog

Re: [PATCH net-next] ip6_tunnel: sit: proper dev_{hold|put} in ndo_[un]init methods

[Eric Dumazet]

On Tue, Mar 30, 2021 at 8:45 AM Eric Dumazet <eric.dumazet@gmail.com> wrote:
>
> From: Eric Dumazet <edumazet@google.com>
>
> Same reasons than for the previous commits :
> 6289a98f0817 ("sit: proper dev_{hold|put} in ndo_[un]init methods")
> 40cb881b5aaa ("ip6_vti: proper dev_{hold|put} in ndo_[un]init methods")
> 7f700334be9a ("ip6_gre: proper dev_{hold|put} in ndo_[un]init methods")
>
> After adopting CONFIG_PCPU_DEV_REFCNT=n option, syzbot was able to trigger
> a warning [1]
>
> Issue here is that:
>
> - all dev_put() should be paired with a corresponding prior dev_hold().
>
> - A driver doing a dev_put() in its ndo_uninit() MUST also
>   do a dev_hold() in its ndo_init(), only when ndo_init()
>   is returning 0.
>
> Otherwise, register_netdevice() would call ndo_uninit()
> in its error path and release a refcount too soon.
>
>

Note to David & Jakub

Can you merge this patch so that I can send my global fix for fallback
tunnels, with a correct Fixes: tag for this patch ?

Thanks !

Re: [PATCH net-next] ip6_tunnel: sit: proper dev_{hold|put} in ndo_[un]init methods

[Eric Dumazet]

[-- Attachment #1: Type: text/plain, Size: 1192 bytes --]

On Wed, Mar 31, 2021 at 8:00 AM Eric Dumazet <edumazet@google.com> wrote:
>
> On Tue, Mar 30, 2021 at 8:45 AM Eric Dumazet <eric.dumazet@gmail.com> wrote:
> >
> > From: Eric Dumazet <edumazet@google.com>
> >
> > Same reasons than for the previous commits :
> > 6289a98f0817 ("sit: proper dev_{hold|put} in ndo_[un]init methods")
> > 40cb881b5aaa ("ip6_vti: proper dev_{hold|put} in ndo_[un]init methods")
> > 7f700334be9a ("ip6_gre: proper dev_{hold|put} in ndo_[un]init methods")
> >
> > After adopting CONFIG_PCPU_DEV_REFCNT=n option, syzbot was able to trigger
> > a warning [1]
> >
> > Issue here is that:
> >
> > - all dev_put() should be paired with a corresponding prior dev_hold().
> >
> > - A driver doing a dev_put() in its ndo_uninit() MUST also
> >   do a dev_hold() in its ndo_init(), only when ndo_init()
> >   is returning 0.
> >
> > Otherwise, register_netdevice() would call ndo_uninit()
> > in its error path and release a refcount too soon.
> >
> >
>
> Note to David & Jakub
>
> Can you merge this patch so that I can send my global fix for fallback
> tunnels, with a correct Fixes: tag for this patch ?
>
> Thanks !

Forgot to attach what the global fix would look like :

[-- Attachment #2: 0001-ipv6-remove-extra-dev_hold-for-fallback-tunnels.patch --]
[-- Type: text/x-patch, Size: 3126 bytes --]

From 2c9cce067a9a1aec32b323ef80179b1856c796af Mon Sep 17 00:00:00 2001
From: Eric Dumazet <edumazet@google.com>
Date: Tue, 30 Mar 2021 13:29:08 -0700
Subject: [PATCH net-next] ipv6: remove extra dev_hold() for fallback tunnels

My previous commits added a dev_hold() in tunnels ndo_init(),
but forgot to remove it from special functions setting up fallback tunnels.

Fallback tunnels do call their respective ndo_init()

This leads to various reports like :

unregister_netdevice: waiting for ip6gre0 to become free. Usage count = 2

Fixes: f21eb0195662 ("ip6_tunnel: sit: proper dev_{hold|put} in ndo_[un]init methods")
Fixes: 6289a98f0817 ("sit: proper dev_{hold|put} in ndo_[un]init methods")
Fixes: 40cb881b5aaa ("ip6_vti: proper dev_{hold|put} in ndo_[un]init methods")
Fixes: 7f700334be9a ("ip6_gre: proper dev_{hold|put} in ndo_[un]init methods")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: syzbot <syzkaller@googlegroups.com>
---
 net/ipv6/ip6_gre.c    | 3 ---
 net/ipv6/ip6_tunnel.c | 1 -
 net/ipv6/ip6_vti.c    | 1 -
 net/ipv6/sit.c        | 1 -
 4 files changed, 6 deletions(-)

diff --git a/net/ipv6/ip6_gre.c b/net/ipv6/ip6_gre.c
index 9689bf9f46f347562330a4d8630c0b0b13a411fc..bc224f917bbd53beb9b8af5bdef3fb9794b8ee44 100644
--- a/net/ipv6/ip6_gre.c
+++ b/net/ipv6/ip6_gre.c
@@ -387,7 +387,6 @@ static struct ip6_tnl *ip6gre_tunnel_locate(struct net *net,
 	if (!(nt->parms.o_flags & TUNNEL_SEQ))
 		dev->features |= NETIF_F_LLTX;
 
-	dev_hold(dev);
 	ip6gre_tunnel_link(ign, nt);
 	return nt;
 
@@ -1539,8 +1538,6 @@ static void ip6gre_fb_tunnel_init(struct net_device *dev)
 	strcpy(tunnel->parms.name, dev->name);
 
 	tunnel->hlen		= sizeof(struct ipv6hdr) + 4;
-
-	dev_hold(dev);
 }
 
 static struct inet6_protocol ip6gre_protocol __read_mostly = {
diff --git a/net/ipv6/ip6_tunnel.c b/net/ipv6/ip6_tunnel.c
index 67ee9d58ec5efcc81e8b27406bd4f57a0caea70b..07a0a06a9b52bc9974e2f36b1477c341c952f94a 100644
--- a/net/ipv6/ip6_tunnel.c
+++ b/net/ipv6/ip6_tunnel.c
@@ -1925,7 +1925,6 @@ static int __net_init ip6_fb_tnl_dev_init(struct net_device *dev)
 	struct ip6_tnl_net *ip6n = net_generic(net, ip6_tnl_net_id);
 
 	t->parms.proto = IPPROTO_IPV6;
-	dev_hold(dev);
 
 	rcu_assign_pointer(ip6n->tnls_wc[0], t);
 	return 0;
diff --git a/net/ipv6/ip6_vti.c b/net/ipv6/ip6_vti.c
index a018afdb3e062c9e664d4ca424176a859f0a332c..856e46ad0895b47b58896852afee3d4a398b139e 100644
--- a/net/ipv6/ip6_vti.c
+++ b/net/ipv6/ip6_vti.c
@@ -963,7 +963,6 @@ static int __net_init vti6_fb_tnl_dev_init(struct net_device *dev)
 	struct vti6_net *ip6n = net_generic(net, vti6_net_id);
 
 	t->parms.proto = IPPROTO_IPV6;
-	dev_hold(dev);
 
 	rcu_assign_pointer(ip6n->tnls_wc[0], t);
 	return 0;
diff --git a/net/ipv6/sit.c b/net/ipv6/sit.c
index 488d3181aec3a5558dbefb6145400627535df761..ff2ca2e7c7f5045663069ea572560d58abee2970 100644
--- a/net/ipv6/sit.c
+++ b/net/ipv6/sit.c
@@ -1470,7 +1470,6 @@ static void __net_init ipip6_fb_tunnel_init(struct net_device *dev)
 	iph->ihl		= 5;
 	iph->ttl		= 64;
 
-	dev_hold(dev);
 	rcu_assign_pointer(sitn->tunnels_wc[0], tunnel);
 }
 
-- 
2.31.0.291.g576ba9dcdaf-goog

Re: [PATCH net-next] ip6_tunnel: sit: proper dev_{hold|put} in ndo_[un]init methods

[David Miller]

From: Eric Dumazet <edumazet@google.com>
Date: Wed, 31 Mar 2021 08:00:24 +0200

> Can you merge this patch so that I can send my global fix for fallback
> tunnels, with a correct Fixes: tag for this patch ?

Done.

Re: [PATCH net-next] ip6_tunnel: sit: proper dev_{hold|put} in ndo_[un]init methods

[Eric Dumazet]

On Wed, Mar 31, 2021 at 11:39 PM David Miller <davem@davemloft.net> wrote:
>
> From: Eric Dumazet <edumazet@google.com>
> Date: Wed, 31 Mar 2021 08:00:24 +0200
>
> > Can you merge this patch so that I can send my global fix for fallback
> > tunnels, with a correct Fixes: tag for this patch ?
>
> Done.

Thanks a lot David, I have sent the followup patch, with updated Fixes: tags.

Re: [PATCH net-next] ip6_tunnel: sit: proper dev_{hold|put} in ndo_[un]init methods

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net-next.git (refs/heads/master):

On Mon, 29 Mar 2021 23:45:51 -0700 you wrote:
> From: Eric Dumazet <edumazet@google.com>
> 
> Same reasons than for the previous commits :
> 6289a98f0817 ("sit: proper dev_{hold|put} in ndo_[un]init methods")
> 40cb881b5aaa ("ip6_vti: proper dev_{hold|put} in ndo_[un]init methods")
> 7f700334be9a ("ip6_gre: proper dev_{hold|put} in ndo_[un]init methods")
> 
> [...]

Here is the summary with links:
  - [net-next] ip6_tunnel: sit: proper dev_{hold|put} in ndo_[un]init methods
    https://git.kernel.org/netdev/net-next/c/48bb5697269a

You are awesome, thank you!
--
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