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

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Date:   Thu, 22 Oct 2020 06:31:06 +0000
From:   "Li, Ke" <keli@...mai.com>
To:     Jakub Kicinski <kuba@...nel.org>
CC:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "edumazet@...gle.com" <edumazet@...gle.com>,
        "kli@...l.edu" <kli@...l.edu>, "Li, Ji" <jli@...mai.com>
Subject: Re: [PATCH net] net: Properly typecast int values to set
 sk_max_pacing_rate

Thanks for review and comment, Jakub!
Please check my v2 patch.

Best,
-Ke

On 10/21/20, 8:53 PM, "Jakub Kicinski" <kuba@...nel.org> wrote:

    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