linux-kernel - Re: [PATCH] samples/seccomp: improve label helper

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Message-ID: <CAL5CW+AHntXxCcQph53kLn8kRZkBjZHEOwCjuHJAVxE-VrFmcQ@mail.gmail.com>
Date:	Tue, 3 Feb 2015 20:35:29 +0100
From:	Robert Swiecki <swiecki@...gle.com>
To:	linux-kernel@...r.kernel.org
Cc:	Kees Cook <keescook@...omium.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] samples/seccomp: improve label helper

>> Fixes a potential corruption with uninitialized stack memory in the seccomp
>> BPF sample program.
>>
>> Reported-by: Robert Swiecki <swiecki@...gle.com>
>> Signed-off-by: Kees Cook <keescook@...omium.org>
>> ---
>>  samples/seccomp/bpf-fancy.c  | 4 +++-
>>  samples/seccomp/bpf-helper.c | 5 +++++
>>  2 files changed, 8 insertions(+), 1 deletion(-)
>>
>> diff --git a/samples/seccomp/bpf-fancy.c b/samples/seccomp/bpf-fancy.c
>> index 8eb483aaec46..e8b24f443709 100644
>> --- a/samples/seccomp/bpf-fancy.c
>> +++ b/samples/seccomp/bpf-fancy.c
>> @@ -25,7 +25,9 @@
>>
>>  int main(int argc, char **argv)
>>  {
>> -       struct bpf_labels l;
>> +       struct bpf_labels l = {
>> +               .count = 0,
>> +       };
>>         static const char msg1[] = "Please type something: ";
>>         static const char msg2[] = "You typed: ";
>>         char buf[256];
>> diff --git a/samples/seccomp/bpf-helper.c b/samples/seccomp/bpf-helper.c
>> index 579cfe331886..f9fa14d81798 100644
>> --- a/samples/seccomp/bpf-helper.c
>> +++ b/samples/seccomp/bpf-helper.c
>> @@ -10,6 +10,7 @@
>>   */
>>
>>  #include <stdio.h>
>> +#include <stdlib.h>
>>  #include <string.h>
>>
>>  #include "bpf-helper.h"
>> @@ -63,6 +64,10 @@ __u32 seccomp_bpf_label(struct bpf_labels *labels, const char *label)
>>  {
>>         struct __bpf_label *begin = labels->labels, *end;
>>         int id;
>> +       if (labels->count == BPF_LABELS_MAX) {
>> +               fprintf(stderr, "Too many labels\n");
>> +               exit(1);
>> +       }
>>         if (labels->count == 0) {
>>                 begin->label = label;
>>                 begin->location = 0xffffffff;
>> --
>> 1.9.1
>>
>>
>> --
>> Kees Cook
>> Chrome OS Security
>
> Hi,
>
> Thanks for the patch!
>
> Not sure if we care, but with a more strict warning/error checking in
> gcc I get now.
>
> seccomp/bpf-helper.c:66:3: error: implicit declaration of function
> ‘exit’ [-Werror=implicit-function-declaration]
>    exit(1);
>    ^
> seccomp/bpf-helper.c:66:3: error: incompatible implicit declaration of
> built-in function ‘exit’ [-Werror]

Ah.. please ignore, I patched my code partially only.

Works well!

-- 
Robert Święcki
--
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