Re: [PATCH net-next v2] net: validate SO_TXTIME clockid coming from userspace

[Willem de Bruijn]

Abhishek Chauhan wrote:
> Currently there are no strict checks while setting SO_TXTIME
> from userspace. With the recent development in skb->tstamp_type
> clockid with unsupported clocks results in warn_on_once, which causes
> unnecessary aborts in some systems which enables panic on warns.
> 
> Add validation in setsockopt to support only CLOCK_REALTIME,
> CLOCK_MONOTONIC and CLOCK_TAI to be set from userspace.
> 
> Link: https://lore.kernel.org/netdev/bc037db4-58bb-4861-ac31-a361a93841d3@xxxxxxxxx/
> Link: https://lore.kernel.org/lkml/6bdba7b6-fd22-4ea5-a356-12268674def1@xxxxxxxxxxx/
> Fixes: 1693c5db6ab8 ("net: Add additional bit to support clockid_t timestamp type")
> Reported-by: syzbot+d7b227731ec589e7f4f0@xxxxxxxxxxxxxxxxxxxxxxxxx
> Closes: https://syzkaller.appspot.com/bug?extid=d7b227731ec589e7f4f0
> Reported-by: syzbot+30a35a2e9c5067cc43fa@xxxxxxxxxxxxxxxxxxxxxxxxx
> Closes: https://syzkaller.appspot.com/bug?extid=30a35a2e9c5067cc43fa
> Signed-off-by: Abhishek Chauhan <quic_abchauha@xxxxxxxxxxx>
> Acked-by: Martin KaFai Lau <martin.lau@xxxxxxxxxx>

Reviewed-by: Willem de Bruijn <willemb@xxxxxxxxxx>

> ---
> Changes since v1 
> - Moved from net to net-next since 
>   Fixes tag is available only on net-next
>   as mentioned by Martin 
> - Added direct link to design discussion as 
>   mentioned by Willem.
> - Parameter in the sockopt_validate_clockid
>   is of type __kernel_clockid_t so changed it from 
>   int to __kernel_clockid_t as mentioned by 
>   Willem.
> - Added Acked-by tag. 
> 
>  net/core/sock.c | 16 ++++++++++++++++
>  1 file changed, 16 insertions(+)
> 
> diff --git a/net/core/sock.c b/net/core/sock.c
> index 8629f9aecf91..d497285f283a 100644
> --- a/net/core/sock.c
> +++ b/net/core/sock.c
> @@ -1083,6 +1083,17 @@ bool sockopt_capable(int cap)
>  }
>  EXPORT_SYMBOL(sockopt_capable);
>  
> +static int sockopt_validate_clockid(__kernel_clockid_t value)

The __kernel variants are UAPI. It looks odd to use this in kernel
internal code, and I don't see many examples immediately.

But I believe it is correct, as we're passing a sock_txtime.clockid
field, which has this (UAPI) type.

> +{
> +	switch (value) {
> +	case CLOCK_REALTIME:
> +	case CLOCK_MONOTONIC:
> +	case CLOCK_TAI:
> +		return 0;
> +	}
> +	return -EINVAL;
> +}
> +
>  /*
>   *	This is meant for all protocols to use and covers goings on
>   *	at the socket level. Everything here is generic.
> @@ -1497,6 +1508,11 @@ int sk_setsockopt(struct sock *sk, int level, int optname,
>  			ret = -EPERM;
>  			break;
>  		}
> +
> +		ret = sockopt_validate_clockid(sk_txtime.clockid);
> +		if (ret)
> +			break;
> +
>  		sock_valbool_flag(sk, SOCK_TXTIME, true);
>  		sk->sk_clockid = sk_txtime.clockid;
>  		sk->sk_txtime_deadline_mode =
> -- 
> 2.25.1
>