Re: [PATCH] arm64/mm: Reject invalid NUMA option

[Steven Rostedt]

On Tue, 28 Apr 2020 10:59:14 +1000
Gavin Shan <gshan@xxxxxxxxxx> wrote:

> Hi Mark,
> 
> On 4/24/20 8:11 PM, Mark Rutland wrote:
> > [Adding Steve, who added str_has_prefix()]
> > 
> > On Fri, Apr 24, 2020 at 02:53:14PM +1000, Gavin Shan wrote:  
> >> The NUMA option is parsed by str_has_prefix() and the invalid option
> >> like "numa=o" can be regarded as "numa=off" wrongly.  
> > 
> > Are you certain that can pass? If that can happen, str_has_prefix() is
> > misnamed and does not seem to do what its kerneldoc says it does, as
> > "off" is not a prefix of "o".
> >   
> 
> Yes, It's possible. str_has_prefix() depends on strncmp(). In this particular
> case, it's equal to the snippet of code as below: strncmp() returns zero.
> str_has_prefix() returns 3.

Wait! strncmp("o", "off", 3) returns zero?

That to me looks like a bug!

This means str_has_prefix() is broken in other areas as well.


> 
> int strncmp(const char *cs, const char *ct, size_t count)
> {
>          unsigned char c1, c2;
> 
>          while (count) {
>                  c1 = *cs++;
>                  c2 = *ct++;
>                  if (c1 != c2)
>                          return c1 < c2 ? -1 : 1;
>                  if (!c1)                             /* break after first character is compared */

Crap! That is totally wrong!

/me goes to fix...

-- Steve

>                          break;
>                  count--;
>          }
>          return 0;                                    /* 0 returned */
> }
> 
> static __always_inline size_t str_has_prefix(const char *str, const char *prefix)
> {
>          size_t len = strlen("o");
>          return strncmp("o", "off", 1) == 0 ? len : 0;
> }
> 
> >> This fixes the issue with sysfs_streq(), which have more sanity checks,
> >> to avoid accepting the invalid options.  
> > 
> > That doesn't sound immediately right, since this is an early parameter,
> > which has nothing to do with sysfs. Perhaps that's just a misleading
> > name?
> >   
> 
> sysfs_streq() was introduced to compare the parameters received from sysfs
> entry, but I don't think it has to be necessarily tied with sysfs entry.
> So the name is bit misleading. Alternatively, we also can fix it in another
> way (as below) if we try to avoid using sysfs_streq().
> 
> diff --git a/arch/arm64/mm/numa.c b/arch/arm64/mm/numa.c
> index 4decf1659700..b0c1ec78f50f 100644
> --- a/arch/arm64/mm/numa.c
> +++ b/arch/arm64/mm/numa.c
> @@ -29,9 +29,13 @@ static __init int numa_parse_early_param(char *opt)
>   {
>          if (!opt)
>                  return -EINVAL;
> -       if (str_has_prefix(opt, "off"))
> +
> +       if (strlen(opt) >= 3 && str_has_prefix(opt, "off"))
>                  numa_off = true;
> 
> > Thanks,
> > Mark.
> >   
> 
> Thanks,
> Gavin
> 
> >> Signed-off-by: Gavin Shan <gshan@xxxxxxxxxx>
> >> ---
> >>   arch/arm64/mm/numa.c | 3 ++-
> >>   1 file changed, 2 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/arch/arm64/mm/numa.c b/arch/arm64/mm/numa.c
> >> index 4decf1659700..bd458b28616a 100644
> >> --- a/arch/arm64/mm/numa.c
> >> +++ b/arch/arm64/mm/numa.c
> >> @@ -29,7 +29,8 @@ static __init int numa_parse_early_param(char *opt)
> >>   {
> >>   	if (!opt)
> >>   		return -EINVAL;
> >> -	if (str_has_prefix(opt, "off"))
> >> +
> >> +	if (sysfs_streq(opt, "off"))
> >>   		numa_off = true;
> >>   
> >>   	return 0;
> >> -- 
> >> 2.23.0
> >>  
> > 
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> > linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
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> >