Messages in this thread | | | Date | Mon, 27 Apr 2020 23:09:20 -0400 | From | Steven Rostedt <> | Subject | Re: [PATCH] arm64/mm: Reject invalid NUMA option |
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On Mon, 27 Apr 2020 22:59:44 -0400 Steven Rostedt <rostedt@goodmis.org> wrote:
> On Mon, 27 Apr 2020 22:54:06 -0400 > Steven Rostedt <rostedt@goodmis.org> wrote: > > > 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! > > Looking at this again, it's not wrong. But how did we get here if c2 isn't > zero as well? >
Could this be a bug in the implementation of strncmp() in arch/arm64/lib/strncmp.S. As I don't know arm64 assembly, I have no idea what it is trying to do.
But strncmp("o","off",3) returning zero *is* a bug.
-- Steve
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