netdev - Re: [PATCH v3 net-next] phonet: do not call synchronize_rcu() from phonet_route

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Message-ID: <ZyuGR3Nfs8v84eKe@nanopsycho.orion>
Date: Wed, 6 Nov 2024 16:07:51 +0100
From: Jiri Pirko <jiri@...nulli.us>
To: Eric Dumazet <edumazet@...gle.com>
Cc: "David S . Miller" <davem@...emloft.net>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	netdev@...r.kernel.org, eric.dumazet@...il.com,
	syzbot <syzkaller@...glegroups.com>,
	Kuniyuki Iwashima <kuniyu@...zon.com>,
	Remi Denis-Courmont <courmisch@...il.com>
Subject: Re: [PATCH v3 net-next] phonet: do not call synchronize_rcu() from
 phonet_route_del()

Wed, Nov 06, 2024 at 02:18:17PM CET, edumazet@...gle.com wrote:
>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@...glegroups.com>
>Signed-off-by: Eric Dumazet <edumazet@...gle.com>
>Reviewed-by: Kuniyuki Iwashima <kuniyu@...zon.com>

Reviewed-by: Jiri Pirko <jiri@...dia.com>