linux-kernel - Re: [PATCH] sysctl: add proper unsigned int support

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Date:   Mon, 30 Jan 2017 15:56:20 +0300
From:   Alexey Dobriyan <adobriyan@...il.com>
To:     "Luis R. Rodriguez" <mcgrof@...nel.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        Ingo Molnar <mingo@...nel.org>, Mel Gorman <mgorman@...e.de>,
        Subash Abhinov Kasiviswanathan <subashab@...eaurora.org>,
        jeyu@...hat.com, Rusty Russell <rusty@...tcorp.com.au>,
        matt@...eblueprint.co.uk, bp@...e.de,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>, shuah@...nel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-kselftest@...r.kernel.org,
        Linux Kernel <linux-kernel@...r.kernel.org>,
        Heinrich Schuchardt <xypron.glpk@....de>,
        Kees Cook <keescook@...omium.org>,
        "David S. Miller" <davem@...emloft.net>,
        Ingo Molnar <mingo@...hat.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH] sysctl: add proper unsigned int support

On Sun, Jan 29, 2017 at 10:29 PM, Luis R. Rodriguez <mcgrof@...nel.org> wrote:
> Commit e7d316a02f6838 ("sysctl: handle error writing UINT_MAX to u32 fields")
> added proc_douintvec() to start help adding support for unsigned int,
> this however was only half the work needed, all these issues are present
> with the current implementation:
>
>   o Printing the values shows a negative value, this happens
>     since do_proc_dointvec() and this uses proc_put_long()
>   o We can easily wrap around the int values: UINT_MAX is
>     4294967295, if we echo in 4294967295 + 1 we end up with 0,
>     using 4294967295 + 2 we end up with 1.
>  o We echo negative values in and they are accepted
>
> Fix all these issues by adding our own do_proc_douintvec().
>
> Cc: Subash Abhinov Kasiviswanathan <subashab@...eaurora.org>
> Cc: Heinrich Schuchardt <xypron.glpk@....de>
> Cc: Kees Cook <keescook@...omium.org>
> Cc: "David S. Miller" <davem@...emloft.net>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Linus Torvalds <torvalds@...ux-foundation.org>
> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Fixes: e7d316a02f68 ("sysctl: handle error writing UINT_MAX to u32 fields")
> Signed-off-by: Luis R. Rodriguez <mcgrof@...nel.org>
> ---
>
> I split this off as its own atomic fix from a larger RFC series [0].
> I've only provided the fix here, and split off further functionality
> into a separate patch for the future. Although this is a fix I don't think
> its super critical, and specially due to its size do not think it can
> be stable material.
>
> I do have proc_douintvec_minmax() but since we have no users for it
> it can wait until I add something that makes use of it. If someone
> needs it now though please let me know.
>
> Likewise adding proc_douintvec_minmax_sysadmin() is very trivial but I have no
> immediate users for it so it can wait even longer.
>
> [0] https://lkml.kernel.org/r/20161208184801.1689-1-mcgrof@kernel.org
>
>  kernel/sysctl.c | 121 +++++++++++++++++++++++++++++++++++++++++++++++++++++---
>  1 file changed, 115 insertions(+), 6 deletions(-)
>
> diff --git a/kernel/sysctl.c b/kernel/sysctl.c
> index 8dbaec0e4f7f..118341d3a139 100644
> --- a/kernel/sysctl.c
> +++ b/kernel/sysctl.c
> @@ -2125,12 +2125,12 @@ static int do_proc_dointvec_conv(bool *negp, unsigned long *lvalp,
>         return 0;
>  }
>
> -static int do_proc_douintvec_conv(bool *negp, unsigned long *lvalp,
> -                                int *valp,
> -                                int write, void *data)
> +static int do_proc_douintvec_conv(unsigned long *lvalp,
> +                                 unsigned int *valp,
> +                                 int write, void *data)
>  {
>         if (write) {
> -               if (*negp)
> +               if (*lvalp > (unsigned long) UINT_MAX)

Cast is unnecessary here.

> +static int __do_proc_douintvec(void *tbl_data, struct ctl_table *table,

> +       for (; left && vleft--; i++, first=false) {

I'd suggest to not implement "array of unsigned int" unless
such sysctl already exists. Much of the complexity arises from this case.