ACK: [SRU Bionic] ip6_gre: proper dev_{hold

[Stefan Bader]

On 08.04.22 15:56, Thadeu Lima de Souza Cascardo wrote:
> From: Eric Dumazet <edumazet at google.com>
> 
> BugLink: https://bugs.launchpad.net/bugs/1968340
> 
> 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 dev_hold(),
>    and vice versa.
> 
> - 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.
> 
> ip6_gre for example (among others problematic drivers)
> has to use dev_hold() in ip6gre_tunnel_init_common()
> instead of from ip6gre_newlink_common(), covering
> both ip6gre_tunnel_init() and ip6gre_tap_init()/
> 
> Note that ip6gre_tunnel_init_common() is not called from
> ip6erspan_tap_init() thus we also need to add a dev_hold() there,
> as ip6erspan_tunnel_uninit() does call dev_put()
> 
> [1]
> refcount_t: decrement hit 0; leaking memory.
> WARNING: CPU: 0 PID: 8422 at lib/refcount.c:31 refcount_warn_saturate+0xbf/0x1e0 lib/refcount.c:31
> Modules linked in:
> CPU: 1 PID: 8422 Comm: syz-executor854 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:ffffc900018befd0 EFLAGS: 00010282
> RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
> RDX: ffff88801ef19c40 RSI: ffffffff815c51f5 RDI: fffff52000317dec
> RBP: 0000000000000004 R08: 0000000000000000 R09: 0000000000000000
> R10: ffffffff815bdf8e R11: 0000000000000000 R12: ffff888018cf4568
> R13: ffff888018cf4c00 R14: ffff8880228f2000 R15: ffffffff8d659b80
> FS:  00000000014eb300(0000) GS:ffff8880b9c00000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 000055d7bf2b3138 CR3: 0000000014933000 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]
>   ip6gre_tunnel_uninit+0x3d7/0x440 net/ipv6/ip6_gre.c:420
>   register_netdevice+0xadf/0x1500 net/core/dev.c:10308
>   ip6gre_newlink_common.constprop.0+0x158/0x410 net/ipv6/ip6_gre.c:1984
>   ip6gre_newlink+0x275/0x7a0 net/ipv6/ip6_gre.c:2017
>   __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
> 
> Fixes: 919067cc845f ("net: add CONFIG_PCPU_DEV_REFCNT")
> Signed-off-by: Eric Dumazet <edumazet at google.com>
> Reported-by: syzbot <syzkaller at googlegroups.com>
> Signed-off-by: David S. Miller <davem at davemloft.net>
> (backported from commit 7f700334be9aeb91d5d86ef9ad2d901b9b453e9b)
> [cascardo: there is no ip6gre_tap_init]
> Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo at canonical.com>
Acked-by: Stefan Bader <stefan.bader at canonical.com>
> ---
>   net/ipv6/ip6_gre.c | 3 +--
>   1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/net/ipv6/ip6_gre.c b/net/ipv6/ip6_gre.c
> index dc9947bed6b8..7c01ac4b8726 100644
> --- a/net/ipv6/ip6_gre.c
> +++ b/net/ipv6/ip6_gre.c
> @@ -1111,6 +1111,7 @@ static int ip6gre_tunnel_init_common(struct net_device *dev)
>   
>   	ip6gre_tnl_init_features(dev);
>   
> +	dev_hold(dev);
>   	return 0;
>   }
>   
> @@ -1440,8 +1441,6 @@ static int ip6gre_newlink_common(struct net *src_net, struct net_device *dev,
>   	if (tb[IFLA_MTU])
>   		ip6_tnl_change_mtu(dev, nla_get_u32(tb[IFLA_MTU]));
>   
> -	dev_hold(dev);
> -
>   out:
>   	return err;
>   }

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