On Wed, Jun 11, 2014 at 3:18 PM, H. Peter Anvin <hpa@xxxxxxxxx> wrote:
> On 06/11/2014 02:56 PM, Andy Lutomirski wrote:
>>
>> 13ns is with the simplest nonempty filter. I hope that empty filters
>> don't work.
>>
>
> Why wouldn't they?
Is it permissible to fall off the end of a BPF program? I'm getting
EINVAL trying to install an actual empty filter. The filter I tested
with was:
#include <unistd.h>
#include <linux/filter.h>
#include <linux/seccomp.h>
#include <sys/syscall.h>
#include <err.h>
#include <sys/prctl.h>
#include <stddef.h>
#include <stdio.h>
int main(int argc, char **argv)
{
int rc;
struct sock_filter filter[] = {
BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_ALLOW),
};
struct sock_fprog prog = {
.len = (unsigned short)(sizeof(filter)/sizeof(filter[0])),
.filter = filter,
};
if (argc < 2) {
printf("Usage: null_seccomp PATH ARGS...\n");
return 1;
}
if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0))
err(1, "PR_SET_NO_NEW_PRIVS");
if (prctl(PR_SET_SECCOMP, SECCOMP_MODE_FILTER, &prog))
err(1, "PR_SET_SECCOMP");
execv(argv[1], argv + 1);
err(1, argv[1]);
}
--Andy
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