| Message ID | 20241104152622.3580037-1-edumazet@google.com (mailing list archive) |
|---|---|
| State | Superseded |
| Delegated to: | Netdev Maintainers |
| Headers | show |
| Series | [net-next] phonet: do not call synchronize_rcu() from phonet_route_del() | expand |
From: Eric Dumazet <edumazet@google.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@googlegroups.com> > Signed-off-by: Eric Dumazet <edumazet@google.com> > Cc: Kuniyuki Iwashima <kuniyu@amazon.com> > Cc: Remi Denis-Courmont <courmisch@gmail.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
On Mon, Nov 4, 2024 at 9:40 PM Kuniyuki Iwashima <kuniyu@amazon.com> wrote: > > From: Eric Dumazet <edumazet@google.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@googlegroups.com> > > Signed-off-by: Eric Dumazet <edumazet@google.com> > > Cc: Kuniyuki Iwashima <kuniyu@amazon.com> > > Cc: Remi Denis-Courmont <courmisch@gmail.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() ? This dev_put() was before your patch. It is paired the dev_hold() in phonet_route_add() > > 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(). Not at all, let's not make phonet slower than needed :)
Le 4 novembre 2024 17:26:22 GMT+02:00, Eric Dumazet <edumazet@google.com> a écrit : >Calling synchronize_rcu() while holding rcu_read_lock() is not >permitted [1] > >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@googlegroups.com> >Signed-off-by: Eric Dumazet <edumazet@google.com> >Cc: Kuniyuki Iwashima <kuniyu@amazon.com> >Cc: Remi Denis-Courmont <courmisch@gmail.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); > 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(); Synchronising after sending notifications sounds a bit iffy. Whatever a given notification is about should be fully committed so we don't create a user-visible race here. Can't we reorder here? > return err; > } >
On Tue, Nov 5, 2024 at 12:05 PM Rémi Denis-Courmont <remi@remlab.net> wrote: > > > > Le 4 novembre 2024 17:26:22 GMT+02:00, Eric Dumazet <edumazet@google.com> a écrit : > >Calling synchronize_rcu() while holding rcu_read_lock() is not > >permitted [1] > > > >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@googlegroups.com> > >Signed-off-by: Eric Dumazet <edumazet@google.com> > >Cc: Kuniyuki Iwashima <kuniyu@amazon.com> > >Cc: Remi Denis-Courmont <courmisch@gmail.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); > > 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(); > > Synchronising after sending notifications sounds a bit iffy. Whatever a given notification is about should be fully committed so we don't create a user-visible race here. > > Can't we reorder here? Fair enough, I will move dev_put() here in V2.
On Tue, Nov 5, 2024 at 12:05 PM Rémi Denis-Courmont <remi@remlab.net> wrote: > > Synchronising after sending notifications sounds a bit iffy. Whatever a given notification is about should be fully committed so we don't create a user-visible race here. This is fine, the notification sends the ifindex, after the route is effectively removed. Fact that the device is held a bit longer than before should be an improvement, or just a nop. However, doing the dev_put() after synchronize_rcu() is probably better.
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); 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; }
Calling synchronize_rcu() while holding rcu_read_lock() is not permitted [1] 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@googlegroups.com> Signed-off-by: Eric Dumazet <edumazet@google.com> Cc: Kuniyuki Iwashima <kuniyu@amazon.com> Cc: Remi Denis-Courmont <courmisch@gmail.com> --- net/phonet/pn_dev.c | 4 +++- net/phonet/pn_netlink.c | 10 ++++++++-- 2 files changed, 11 insertions(+), 3 deletions(-)