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Miller" , Jakub Kicinski , Paolo Abeni , netdev@vger.kernel.org, eric.dumazet@gmail.com, syzbot , Jiri Pirko Subject: Re: [PATCH net-next] inet6: expand rcu_read_lock() scope in inet6_dump_addr() Message-ID: References: <20240227222259.4081489-1-edumazet@google.com> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240227222259.4081489-1-edumazet@google.com> Tue, Feb 27, 2024 at 11:22:59PM CET, edumazet@google.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: > > __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 >Signed-off-by: Eric Dumazet >Cc: Jiri Pirko Reviewed-by: Jiri Pirko