netdev - Re: [PATCH net] netlink: annotate lockless accesses to nlk->max_recvmsg

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Date:   Tue, 4 Apr 2023 17:10:54 +0200
From:   Simon Horman <simon.horman@...igine.com>
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>
Subject: Re: [PATCH net] netlink: annotate lockless accesses to
 nlk->max_recvmsg_len

On Mon, Apr 03, 2023 at 09:46:43PM +0000, Eric Dumazet wrote:
> syzbot reported a data-race in data-race in netlink_recvmsg() [1]
> 
> Indeed, netlink_recvmsg() can be run concurrently,
> and netlink_dump() also needs protection.
> 
> [1]
> BUG: KCSAN: data-race in netlink_recvmsg / netlink_recvmsg
> 
> read to 0xffff888141840b38 of 8 bytes by task 23057 on cpu 0:
> netlink_recvmsg+0xea/0x730 net/netlink/af_netlink.c:1988
> sock_recvmsg_nosec net/socket.c:1017 [inline]
> sock_recvmsg net/socket.c:1038 [inline]
> __sys_recvfrom+0x1ee/0x2e0 net/socket.c:2194
> __do_sys_recvfrom net/socket.c:2212 [inline]
> __se_sys_recvfrom net/socket.c:2208 [inline]
> __x64_sys_recvfrom+0x78/0x90 net/socket.c:2208
> do_syscall_x64 arch/x86/entry/common.c:50 [inline]
> do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
> entry_SYSCALL_64_after_hwframe+0x63/0xcd
> 
> write to 0xffff888141840b38 of 8 bytes by task 23037 on cpu 1:
> netlink_recvmsg+0x114/0x730 net/netlink/af_netlink.c:1989
> sock_recvmsg_nosec net/socket.c:1017 [inline]
> sock_recvmsg net/socket.c:1038 [inline]
> ____sys_recvmsg+0x156/0x310 net/socket.c:2720
> ___sys_recvmsg net/socket.c:2762 [inline]
> do_recvmmsg+0x2e5/0x710 net/socket.c:2856
> __sys_recvmmsg net/socket.c:2935 [inline]
> __do_sys_recvmmsg net/socket.c:2958 [inline]
> __se_sys_recvmmsg net/socket.c:2951 [inline]
> __x64_sys_recvmmsg+0xe2/0x160 net/socket.c:2951
> do_syscall_x64 arch/x86/entry/common.c:50 [inline]
> do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
> entry_SYSCALL_64_after_hwframe+0x63/0xcd
> 
> value changed: 0x0000000000000000 -> 0x0000000000001000
> 
> Reported by Kernel Concurrency Sanitizer on:
> CPU: 1 PID: 23037 Comm: syz-executor.2 Not tainted 6.3.0-rc4-syzkaller-00195-g5a57b48fdfcb #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/02/2023
> 
> Fixes: 9063e21fb026 ("netlink: autosize skb lengthes")
> Reported-by: syzbot <syzkaller@...glegroups.com>
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>

Reviewed-by: Simon Horman <simon.horman@...igine.com>