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SubjectRe: [PATCH] arm64/mm: Reject invalid NUMA option
On Tue, 28 Apr 2020 10:59:14 +1000
Gavin Shan <gshan@redhat.com> 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@redhat.com>
> >> ---
> >> 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
> >>
> >
> > _______________________________________________
> > linux-arm-kernel mailing list
> > linux-arm-kernel@lists.infradead.org
> > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
> >

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