netdev - Re: [PATCH net-next] inet6: expand rcu_read_lock() scope in inet6_dump

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Date: Wed, 28 Feb 2024 08:39:03 +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>, Jiri Pirko <jiri@...dia.com>
Subject: Re: [PATCH net-next] inet6: expand rcu_read_lock() scope in
 inet6_dump_addr()

Tue, Feb 27, 2024 at 11:22:59PM CET, edumazet@...gle.com wrote:
>I missed that inet6_dump_addr() is calling in6_dump_addrs()
>from two points.
>
>First one under RTNL protection, and second one under rcu_read_lock().
>
>Since we want to remove RTNL use from inet6_dump_addr() very soon,
>no longer assume in6_dump_addrs() is protected by RTNL (even
>if this is still the case).
>
>Use rcu_read_lock() earlier to fix this lockdep splat:
>
>WARNING: suspicious RCU usage
>6.8.0-rc5-syzkaller-01618-gf8cbf6bde4c8 #0 Not tainted
>
>net/ipv6/addrconf.c:5317 suspicious rcu_dereference_check() usage!
>
>other info that might help us debug this:
>
>rcu_scheduler_active = 2, debug_locks = 1
>3 locks held by syz-executor.2/8834:
>  #0: ffff88802f554678 (nlk_cb_mutex-ROUTE){+.+.}-{3:3}, at: __netlink_dump_start+0x119/0x780 net/netlink/af_netlink.c:2338
>  #1: ffffffff8f377a88 (rtnl_mutex){+.+.}-{3:3}, at: netlink_dump+0x676/0xda0 net/netlink/af_netlink.c:2265
>  #2: ffff88807e5f0580 (&ndev->lock){++--}-{2:2}, at: in6_dump_addrs+0xb8/0x1de0 net/ipv6/addrconf.c:5279
>
>stack backtrace:
>CPU: 1 PID: 8834 Comm: syz-executor.2 Not tainted 6.8.0-rc5-syzkaller-01618-gf8cbf6bde4c8 #0
>Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/25/2024
>Call Trace:
> <TASK>
>  __dump_stack lib/dump_stack.c:88 [inline]
>  dump_stack_lvl+0x1e7/0x2e0 lib/dump_stack.c:106
>  lockdep_rcu_suspicious+0x220/0x340 kernel/locking/lockdep.c:6712
>  in6_dump_addrs+0x1b47/0x1de0 net/ipv6/addrconf.c:5317
>  inet6_dump_addr+0x1597/0x1690 net/ipv6/addrconf.c:5428
>  netlink_dump+0x6a6/0xda0 net/netlink/af_netlink.c:2266
>  __netlink_dump_start+0x59d/0x780 net/netlink/af_netlink.c:2374
>  netlink_dump_start include/linux/netlink.h:340 [inline]
>  rtnetlink_rcv_msg+0xcf7/0x10d0 net/core/rtnetlink.c:6555
>  netlink_rcv_skb+0x1e3/0x430 net/netlink/af_netlink.c:2547
>  netlink_unicast_kernel net/netlink/af_netlink.c:1335 [inline]
>  netlink_unicast+0x7ea/0x980 net/netlink/af_netlink.c:1361
>  netlink_sendmsg+0x8e0/0xcb0 net/netlink/af_netlink.c:1902
>  sock_sendmsg_nosec net/socket.c:730 [inline]
>  __sock_sendmsg+0x221/0x270 net/socket.c:745
>  ____sys_sendmsg+0x525/0x7d0 net/socket.c:2584
>  ___sys_sendmsg net/socket.c:2638 [inline]
>  __sys_sendmsg+0x2b0/0x3a0 net/socket.c:2667
>
>Fixes: c3718936ec47 ("ipv6: anycast: complete RCU handling of struct ifacaddr6")
>Reported-by: syzbot <syzkaller@...glegroups.com>
>Signed-off-by: Eric Dumazet <edumazet@...gle.com>
>Cc: Jiri Pirko <jiri@...dia.com>

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