netdev - Re: [PATCH net-next] phonet: do not call synchronize_rcu() from phonet_route

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Message-ID: <20241104204005.86813-1-kuniyu@amazon.com>
Date: Mon, 4 Nov 2024 12:40:05 -0800
From: Kuniyuki Iwashima <kuniyu@...zon.com>
To: <edumazet@...gle.com>
CC: <courmisch@...il.com>, <davem@...emloft.net>, <eric.dumazet@...il.com>,
	<kuba@...nel.org>, <kuniyu@...zon.com>, <netdev@...r.kernel.org>,
	<pabeni@...hat.com>, <syzkaller@...glegroups.com>
Subject: Re: [PATCH net-next] phonet: do not call synchronize_rcu() from phonet_route_del()

From: Eric Dumazet <edumazet@...gle.com>
Date: Mon,  4 Nov 2024 15:26:22 +0000
> Calling synchronize_rcu() while holding rcu_read_lock() is not
> permitted [1]

Thanks for catching this !

> 
> Move the synchronize_rcu() to route_doit().
> 
> [1]
> WARNING: suspicious RCU usage
> 6.12.0-rc5-syzkaller-01056-gf07a6e6ceb05 #0 Not tainted
> -----------------------------
> kernel/rcu/tree.c:4092 Illegal synchronize_rcu() in RCU read-side critical section!
> 
> other info that might help us debug this:
> 
> rcu_scheduler_active = 2, debug_locks = 1
> 1 lock held by syz-executor427/5840:
>   #0: ffffffff8e937da0 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire include/linux/rcupdate.h:337 [inline]
>   #0: ffffffff8e937da0 (rcu_read_lock){....}-{1:2}, at: rcu_read_lock include/linux/rcupdate.h:849 [inline]
>   #0: ffffffff8e937da0 (rcu_read_lock){....}-{1:2}, at: route_doit+0x3d6/0x640 net/phonet/pn_netlink.c:264
> 
> stack backtrace:
> CPU: 1 UID: 0 PID: 5840 Comm: syz-executor427 Not tainted 6.12.0-rc5-syzkaller-01056-gf07a6e6ceb05 #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/13/2024
> Call Trace:
>  <TASK>
>   __dump_stack lib/dump_stack.c:94 [inline]
>   dump_stack_lvl+0x241/0x360 lib/dump_stack.c:120
>   lockdep_rcu_suspicious+0x226/0x340 kernel/locking/lockdep.c:6821
>   synchronize_rcu+0xea/0x360 kernel/rcu/tree.c:4089
>   phonet_route_del+0xc6/0x140 net/phonet/pn_dev.c:409
>   route_doit+0x514/0x640 net/phonet/pn_netlink.c:275
>   rtnetlink_rcv_msg+0x791/0xcf0 net/core/rtnetlink.c:6790
>   netlink_rcv_skb+0x1e3/0x430 net/netlink/af_netlink.c:2551
>   netlink_unicast_kernel net/netlink/af_netlink.c:1331 [inline]
>   netlink_unicast+0x7f6/0x990 net/netlink/af_netlink.c:1357
>   netlink_sendmsg+0x8e4/0xcb0 net/netlink/af_netlink.c:1901
>   sock_sendmsg_nosec net/socket.c:729 [inline]
>   __sock_sendmsg+0x221/0x270 net/socket.c:744
>   sock_write_iter+0x2d7/0x3f0 net/socket.c:1165
>   new_sync_write fs/read_write.c:590 [inline]
>   vfs_write+0xaeb/0xd30 fs/read_write.c:683
>   ksys_write+0x183/0x2b0 fs/read_write.c:736
>   do_syscall_x64 arch/x86/entry/common.c:52 [inline]
>   do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> 
> Fixes: 17a1ac0018ae ("phonet: Don't hold RTNL for route_doit().")
> Reported-by: syzbot <syzkaller@...glegroups.com>
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Cc: Kuniyuki Iwashima <kuniyu@...zon.com>
> Cc: Remi Denis-Courmont <courmisch@...il.com>
> ---
>  net/phonet/pn_dev.c     |  4 +++-
>  net/phonet/pn_netlink.c | 10 ++++++++--
>  2 files changed, 11 insertions(+), 3 deletions(-)
> 
> diff --git a/net/phonet/pn_dev.c b/net/phonet/pn_dev.c
> index 19234d664c4fb537eba0267266efbb226cf103c3..578d935f2b11694fd1004c5f854ec344b846eeb2 100644
> --- a/net/phonet/pn_dev.c
> +++ b/net/phonet/pn_dev.c
> @@ -406,7 +406,9 @@ int phonet_route_del(struct net_device *dev, u8 daddr)
>  
>  	if (!dev)
>  		return -ENOENT;
> -	synchronize_rcu();
> +
> +	/* Note : our caller must call synchronize_rcu() */
> +
>  	dev_put(dev);

Are these synchronize_rcu() + dev_put() paired with rcu_read_lock()
and dev_hold() in phonet_route_output() ?

If so, we need to move dev_put() too or maybe we can remove
synchronize_rcu() here and replace rcu_read_lock() with
spin_lock(&routes->lock) in phonet_route_output().


>  	return 0;
>  }
> diff --git a/net/phonet/pn_netlink.c b/net/phonet/pn_netlink.c
> index ca1f04e4a2d9eb3b2a6d6cc5b299aee28d569b08..24930733ac572ed3ec5fd142d347c115346a28fa 100644
> --- a/net/phonet/pn_netlink.c
> +++ b/net/phonet/pn_netlink.c
> @@ -233,6 +233,7 @@ static int route_doit(struct sk_buff *skb, struct nlmsghdr *nlh,
>  {
>  	struct net *net = sock_net(skb->sk);
>  	struct nlattr *tb[RTA_MAX+1];
> +	bool sync_needed = false;
>  	struct net_device *dev;
>  	struct rtmsg *rtm;
>  	u32 ifindex;
> @@ -269,16 +270,21 @@ static int route_doit(struct sk_buff *skb, struct nlmsghdr *nlh,
>  		return -ENODEV;
>  	}
>  
> -	if (nlh->nlmsg_type == RTM_NEWROUTE)
> +	if (nlh->nlmsg_type == RTM_NEWROUTE) {
>  		err = phonet_route_add(dev, dst);
> -	else
> +	} else {
>  		err = phonet_route_del(dev, dst);
> +		if (!err)
> +			sync_needed = true;
> +	}
>  
>  	rcu_read_unlock();
>  
>  	if (!err)
>  		rtm_phonet_notify(net, nlh->nlmsg_type, ifindex, dst);
>  
> +	if (sync_needed)
> +		synchronize_rcu();
>  	return err;
>  }
>  
> -- 
> 2.47.0.163.g1226f6d8fa-goog