netdev - Re: [PATCH net v2] net: Properly typecast int values to set sk_max_pacing

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Date:   Thu, 22 Oct 2020 08:43:46 +0000
From:   "Li, Ke" <keli@...mai.com>
To:     Eric Dumazet <edumazet@...gle.com>
CC:     netdev <netdev@...r.kernel.org>,
        David Miller <davem@...emloft.net>,
        "Jakub Kicinski" <kuba@...nel.org>, "kli@...l.edu" <kli@...l.edu>,
        "Li, Ji" <jli@...mai.com>
Subject: Re: [PATCH net v2] net: Properly typecast int values to set
 sk_max_pacing_rate

Thank you, Eric!

Nice to know the recent change to wrap-at-100. Will this be reflected somewhere, like, in Documentation/process/coding-style.rst?

Best,
-Ke

On 10/22/20, 12:49 AM, "Eric Dumazet" <edumazet@...gle.com> wrote:

    On Thu, Oct 22, 2020 at 8:42 AM Ke Li <keli@...mai.com> 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>
    > ---
    > v2: wrap the line in net/core/filter.c to less than 80 chars.

    SGTM (the other version was also fine, the 80 chars rule has been
    relaxed/changed to 100 recently)

    Reviewed-by: Eric Dumazet <edumazet@...gle.com>