Re: [PATCH net] tcp: restrict net.ipv4.tcp_app_win

[Kuniyuki Iwashima]

From:   YueHaibing <yuehaibing@xxxxxxxxxx>
Date:   Thu, 6 Apr 2023 14:34:50 +0800
> UBSAN: shift-out-of-bounds in net/ipv4/tcp_input.c:555:23
> shift exponent 255 is too large for 32-bit type 'int'
> CPU: 1 PID: 7907 Comm: ssh Not tainted 6.3.0-rc4-00161-g62bad54b26db-dirty #206
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014
> Call Trace:
>  <TASK>
>  dump_stack_lvl+0x136/0x150
>  __ubsan_handle_shift_out_of_bounds+0x21f/0x5a0
>  tcp_init_transfer.cold+0x3a/0xb9
>  tcp_finish_connect+0x1d0/0x620
>  tcp_rcv_state_process+0xd78/0x4d60
>  tcp_v4_do_rcv+0x33d/0x9d0
>  __release_sock+0x133/0x3b0
>  release_sock+0x58/0x1b0
> 
> 'maxwin' is int, shifting int for 32 or more bits is undefined behaviour.
> 
> Signed-off-by: YueHaibing <yuehaibing@xxxxxxxxxx>

Reviewed-by: Kuniyuki Iwashima <kuniyu@xxxxxxxxxx>

Thanks!

> ---
>  Documentation/networking/ip-sysctl.rst | 2 ++
>  net/ipv4/sysctl_net_ipv4.c             | 3 +++
>  2 files changed, 5 insertions(+)
> 
> diff --git a/Documentation/networking/ip-sysctl.rst b/Documentation/networking/ip-sysctl.rst
> index 87dd1c5283e6..58a78a316697 100644
> --- a/Documentation/networking/ip-sysctl.rst
> +++ b/Documentation/networking/ip-sysctl.rst
> @@ -340,6 +340,8 @@ tcp_app_win - INTEGER
>  	Reserve max(window/2^tcp_app_win, mss) of window for application
>  	buffer. Value 0 is special, it means that nothing is reserved.
>  
> +	Possible values are [0, 31], inclusive.
> +
>  	Default: 31
>  
>  tcp_autocorking - BOOLEAN
> diff --git a/net/ipv4/sysctl_net_ipv4.c b/net/ipv4/sysctl_net_ipv4.c
> index 0d0cc4ef2b85..40fe70fc2015 100644
> --- a/net/ipv4/sysctl_net_ipv4.c
> +++ b/net/ipv4/sysctl_net_ipv4.c
> @@ -25,6 +25,7 @@ static int ip_local_port_range_min[] = { 1, 1 };
>  static int ip_local_port_range_max[] = { 65535, 65535 };
>  static int tcp_adv_win_scale_min = -31;
>  static int tcp_adv_win_scale_max = 31;
> +static int tcp_app_win_max = 31;
>  static int tcp_min_snd_mss_min = TCP_MIN_SND_MSS;
>  static int tcp_min_snd_mss_max = 65535;
>  static int ip_privileged_port_min;
> @@ -1198,6 +1199,8 @@ static struct ctl_table ipv4_net_table[] = {
>  		.maxlen		= sizeof(u8),
>  		.mode		= 0644,
>  		.proc_handler	= proc_dou8vec_minmax,
> +		.extra1		= SYSCTL_ZERO,
> +		.extra2		= &tcp_app_win_max,
>  	},
>  	{
>  		.procname	= "tcp_adv_win_scale",
> -- 
> 2.34.1