netdev - Re: [PATCH net] net: Properly typecast int values to set sk_max_pacing

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Date:   Wed, 21 Oct 2020 20:53:20 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Ke Li <keli@...mai.com>
Cc:     <netdev@...r.kernel.org>, <davem@...emloft.net>,
        <edumazet@...gle.com>, <kli@...l.edu>, Ji Li <jli@...mai.com>
Subject: Re: [PATCH net] net: Properly typecast int values to set
 sk_max_pacing_rate

On Mon, 19 Oct 2020 20:31:49 -0400 Ke Li wrote:
> In setsockopt(SO_MAX_PACING_RATE) on 64bit systems, sk_max_pacing_rate,
> after extended from 'u32' to 'unsigned long', takes unintentionally
> hiked value whenever assigned from an 'int' value with MSB=1, due to
> binary sign extension in promoting s32 to u64, e.g. 0x80000000 becomes
> 0xFFFFFFFF80000000.
> 
> Thus inflated sk_max_pacing_rate causes subsequent getsockopt to return
> ~0U unexpectedly. It may also result in increased pacing rate.
> 
> Fix by explicitly casting the 'int' value to 'unsigned int' before
> assigning it to sk_max_pacing_rate, for zero extension to happen.
> 
> Fixes: 76a9ebe811fb ("net: extend sk_pacing_rate to unsigned long")
> Signed-off-by: Ji Li <jli@...mai.com>
> Signed-off-by: Ke Li <keli@...mai.com>
> Cc: Eric Dumazet <edumazet@...gle.com>
> ---
>  net/core/filter.c | 2 +-
>  net/core/sock.c   | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/net/core/filter.c b/net/core/filter.c
> index c5e2a1c5fd8d..43f20c14864c 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -4693,7 +4693,7 @@ static int _bpf_setsockopt(struct sock *sk, int level, int optname,
>  				cmpxchg(&sk->sk_pacing_status,
>  					SK_PACING_NONE,
>  					SK_PACING_NEEDED);
> -			sk->sk_max_pacing_rate = (val == ~0U) ? ~0UL : val;
> +			sk->sk_max_pacing_rate = (val == ~0U) ? ~0UL : (unsigned int)val;

Looks good, but please wrap this to 80 chars.

>  			sk->sk_pacing_rate = min(sk->sk_pacing_rate,
>  						 sk->sk_max_pacing_rate);
>  			break;
> diff --git a/net/core/sock.c b/net/core/sock.c
> index 4e8729357122..727ea1cc633c 100644
> --- a/net/core/sock.c
> +++ b/net/core/sock.c
> @@ -1163,7 +1163,7 @@ int sock_setsockopt(struct socket *sock, int level, int optname,
>  
>  	case SO_MAX_PACING_RATE:
>  		{
> -		unsigned long ulval = (val == ~0U) ? ~0UL : val;
> +		unsigned long ulval = (val == ~0U) ? ~0UL : (unsigned int)val;
>  
>  		if (sizeof(ulval) != sizeof(val) &&
>  		    optlen >= sizeof(ulval) &&
> 
> base-commit: 0e8b8d6a2d85344d80dda5beadd98f5f86e8d3d3