[PATCH v2 net] phonet: do not call synchronize_rcu() from phonet_route_del()

[PATCH v2 net] phonet: do not call synchronize_rcu() from phonet_route_del()

[Eric Dumazet]

Calling synchronize_rcu() while holding rcu_read_lock() is not
permitted [1]

Move the synchronize_rcu() + dev_put() to route_doit().

Alternative would be to not use rcu_read_lock() in 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@googlegroups.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Kuniyuki Iwashima <kuniyu@amazon.com>
Cc: Remi Denis-Courmont <courmisch@gmail.com>
---
v2: also move dev_put() to keep it after synchronize_rcu()

 net/phonet/pn_dev.c     |  5 +++--
 net/phonet/pn_netlink.c | 12 ++++++++++--
 2 files changed, 13 insertions(+), 4 deletions(-)

diff --git a/net/phonet/pn_dev.c b/net/phonet/pn_dev.c
index 19234d664c4fb537eba0267266efbb226cf103c3..5c36bae37b8fa85d2e97bf11d099c6c8599dcc5f 100644
--- a/net/phonet/pn_dev.c
+++ b/net/phonet/pn_dev.c
@@ -406,8 +406,9 @@ int phonet_route_del(struct net_device *dev, u8 daddr)
 
 	if (!dev)
 		return -ENOENT;
-	synchronize_rcu();
-	dev_put(dev);
+
+	/* Note : our caller must call synchronize_rcu() and dev_put(dev) */
+
 	return 0;
 }
 
diff --git a/net/phonet/pn_netlink.c b/net/phonet/pn_netlink.c
index ca1f04e4a2d9eb3b2a6d6cc5b299aee28d569b08..b9043c92dc246f8c5c313b262eb3ec4afad47ecb 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;
@@ -269,13 +270,20 @@ 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 (sync_needed) {
+		synchronize_rcu();
+		dev_put(dev);
+	}
 	if (!err)
 		rtm_phonet_notify(net, nlh->nlmsg_type, ifindex, dst);
 
-- 
2.47.0.199.ga7371fff76-goog

Re: [PATCH v2 net] phonet: do not call synchronize_rcu() from phonet_route_del()

[Kuniyuki Iwashima]

From: Eric Dumazet <edumazet@google.com>
Date: Tue,  5 Nov 2024 13:26:45 +0000
> Calling synchronize_rcu() while holding rcu_read_lock() is not
> permitted [1]
> 
> Move the synchronize_rcu() + dev_put() to route_doit().
> 
> Alternative would be to not use rcu_read_lock() in 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@googlegroups.com>
> Signed-off-by: Eric Dumazet <edumazet@google.com>

Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>

Thanks!


> Cc: Kuniyuki Iwashima <kuniyu@amazon.com>
> Cc: Remi Denis-Courmont <courmisch@gmail.com>
> ---
> v2: also move dev_put() to keep it after synchronize_rcu()
> 
>  net/phonet/pn_dev.c     |  5 +++--
>  net/phonet/pn_netlink.c | 12 ++++++++++--
>  2 files changed, 13 insertions(+), 4 deletions(-)
> 
> diff --git a/net/phonet/pn_dev.c b/net/phonet/pn_dev.c
> index 19234d664c4fb537eba0267266efbb226cf103c3..5c36bae37b8fa85d2e97bf11d099c6c8599dcc5f 100644
> --- a/net/phonet/pn_dev.c
> +++ b/net/phonet/pn_dev.c
> @@ -406,8 +406,9 @@ int phonet_route_del(struct net_device *dev, u8 daddr)
>  
>  	if (!dev)
>  		return -ENOENT;
> -	synchronize_rcu();
> -	dev_put(dev);
> +
> +	/* Note : our caller must call synchronize_rcu() and dev_put(dev) */
> +
>  	return 0;
>  }
>  
> diff --git a/net/phonet/pn_netlink.c b/net/phonet/pn_netlink.c
> index ca1f04e4a2d9eb3b2a6d6cc5b299aee28d569b08..b9043c92dc246f8c5c313b262eb3ec4afad47ecb 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;
> @@ -269,13 +270,20 @@ 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 (sync_needed) {
> +		synchronize_rcu();
> +		dev_put(dev);
> +	}
>  	if (!err)
>  		rtm_phonet_notify(net, nlh->nlmsg_type, ifindex, dst);
>  
> -- 
> 2.47.0.199.ga7371fff76-goog

Re: [PATCH v2 net] phonet: do not call synchronize_rcu() from phonet_route_del()

[Jakub Kicinski]

On Tue,  5 Nov 2024 13:26:45 +0000 Eric Dumazet wrote:
> Calling synchronize_rcu() while holding rcu_read_lock() is not
> permitted [1]

Doesn't apply to net, looks like it diverged in net-next
-- 
pw-bot: cr

Re: [PATCH v2 net] phonet: do not call synchronize_rcu() from phonet_route_del()

[Eric Dumazet]

On Wed, Nov 6, 2024 at 3:25 AM Jakub Kicinski <kuba@kernel.org> wrote:
>
> On Tue,  5 Nov 2024 13:26:45 +0000 Eric Dumazet wrote:
> > Calling synchronize_rcu() while holding rcu_read_lock() is not
> > permitted [1]
>
> Doesn't apply to net, looks like it diverged in net-next
> --
> pw-bot: cr

V1 was properly sent to net-next, but for some reason I sent v2 with
the wrong 'net' annotation.