code review 7480046: net: never use backlog > 65535

net: never use backlog > 65535

The system call takes an int, but the kernel stores it in a uint16.
At least one Linux system sets /proc/sys/net/core/somaxconn
to 262144, which ends up being 0 in the uint16. Avoid being tricked.

FreeBSD sources also store the backlog in a uint16.
Assume the problem is systemic and fix it everywhere.

Fixes issue 5030.

[rsc, 2013-03-12 05:32:29]

Hello golang-dev@googlegroups.com,

I'd like you to review this change to
https://code.google.com/p/go/

[bradfitz, 2013-03-12 05:35:41]

LGTM

nice.

On Mon, Mar 11, 2013 at 10:32 PM, <rsc@golang.org> wrote:

> Reviewers: golang-dev1,
>
> Message:
> Hello golang-dev@googlegroups.com,
>
> I'd like you to review this change to
> https://code.google.com/p/go/
>
>
> Description:
> net: never use backlog > 65535
>
> The system call takes an int, but the kernel stores it in a uint16.
> At least one Linux system sets /proc/sys/net/core/somaxconn
> to 262144, which ends up being 0 in the uint16. Avoid being tricked.
>
> FreeBSD sources also store the backlog in a uint16.
> Assume the problem is systemic and fix it everywhere.
>
> Fixes issue 5030.
>
> Please review this at
https://codereview.appspot.**com/7480046/<https://codereview.appspot.com/7480...
>
> Affected files:
>   M src/pkg/net/sock_bsd.go
>   M src/pkg/net/sock_linux.go
>   M src/pkg/net/sock_windows.go
>
>
> Index: src/pkg/net/sock_bsd.go
> ==============================**==============================**=======
> --- a/src/pkg/net/sock_bsd.go
> +++ b/src/pkg/net/sock_bsd.go
> @@ -27,5 +27,11 @@
>         if n == 0 || err != nil {
>                 return syscall.SOMAXCONN
>         }
> +       // FreeBSD stores the backlog in a uint16, as does Linux.
> +       // Assume the other BSDs do too. Truncate number to avoid wrapping.
> +       // See issue 5030.
> +       if n > 1<<16-1 {
> +               n = 1<<16 - 1
> +       }
>         return int(n)
>  }
> Index: src/pkg/net/sock_linux.go
> ==============================**==============================**=======
> --- a/src/pkg/net/sock_linux.go
> +++ b/src/pkg/net/sock_linux.go
> @@ -21,5 +21,11 @@
>         if n == 0 || !ok {
>                 return syscall.SOMAXCONN
>         }
> +       // Linux stores the backlog in a uint16.
> +       // Truncate number to avoid wrapping.
> +       // See issue 5030.
> +       if n > 1<<16-1 {
> +               n = 1<<16 - 1
> +       }
>         return n
>  }
> Index: src/pkg/net/sock_windows.go
> ==============================**==============================**=======
> --- a/src/pkg/net/sock_windows.go
> +++ b/src/pkg/net/sock_windows.go
> @@ -8,6 +8,7 @@
>
>  func maxListenerBacklog() int {
>         // TODO: Implement this
> +       // NOTE: Never return a number bigger than 1<<16 - 1. See issue
> 5030.
>         return syscall.SOMAXCONN
>  }
>
>
>
> --
>
> ---You received this message because you are subscribed to the Google
> Groups "golang-dev" group.
> To unsubscribe from this group and stop receiving emails from it, send an
> email to
golang-dev+unsubscribe@**googlegroups.com<golang-dev%2Bunsubscribe@googlegrou...
> .
> For more options, visit
https://groups.google.com/**groups/opt_out<https://groups.google.com/groups/o...
> .
>
>
>

[rsc, 2013-03-12 05:48:56]

*** Submitted as https://code.google.com/p/go/source/detail?r=d515b37f8bb5 ***

net: never use backlog > 65535

The system call takes an int, but the kernel stores it in a uint16.
At least one Linux system sets /proc/sys/net/core/somaxconn
to 262144, which ends up being 0 in the uint16. Avoid being tricked.

FreeBSD sources also store the backlog in a uint16.
Assume the problem is systemic and fix it everywhere.

Fixes issue 5030.

R=golang-dev, bradfitz
CC=golang-dev
https://codereview.appspot.com/7480046