Re: [PATCH] sysctl: add proper unsigned int support

[Alexey Dobriyan]

On Sun, Jan 29, 2017 at 10:29 PM, Luis R. Rodriguez <mcgrof@xxxxxxxxxx> 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@xxxxxxxxxxxxxx>
> Cc: Heinrich Schuchardt <xypron.glpk@xxxxxx>
> Cc: Kees Cook <keescook@xxxxxxxxxxxx>
> Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> Fixes: e7d316a02f68 ("sysctl: handle error writing UINT_MAX to u32 fields")
> Signed-off-by: Luis R. Rodriguez <mcgrof@xxxxxxxxxx>
> ---
>
> 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@xxxxxxxxxx
>
>  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.