linux-kernel - Re: [PATCH] selftests/seccomp: Be more precise with syscall arguments.

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Date:	Mon, 2 Nov 2015 11:49:27 -0800
From:	Kees Cook <keescook@...omium.org>
To:	Shuah Khan <shuahkh@....samsung.com>
Cc:	Robert Sesek <rsesek@...gle.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] selftests/seccomp: Be more precise with syscall arguments.

On Mon, Nov 2, 2015 at 10:50 AM, Robert Sesek <rsesek@...gle.com> wrote:
> Certain syscall emulation layers strictly check that the number of
> arguments match what the syscall handler expects. The KILL_one_arg_one and
> KILL_one_arg_six tests passed more parameters than expected to various
> syscalls, causing failures in this emulation mode. Instead, test using
> syscalls that take the appropriate number of arguments.
>
> Signed-off-by: Robert Sesek <rsesek@...gle.com>

Signed-off-by: Kees Cook <keescook@...omium.org>

Looks great, thanks!

Shuah, can you take this into the selftests tree?

-Kees

> ---
>  tools/testing/selftests/seccomp/seccomp_bpf.c | 46 ++++++++++++++++++++-------
>  1 file changed, 35 insertions(+), 11 deletions(-)
>
> diff --git a/tools/testing/selftests/seccomp/seccomp_bpf.c b/tools/testing/selftests/seccomp/seccomp_bpf.c
> index e7bc5d3..e38cc54 100644
> --- a/tools/testing/selftests/seccomp/seccomp_bpf.c
> +++ b/tools/testing/selftests/seccomp/seccomp_bpf.c
> @@ -29,6 +29,9 @@
>  #include <linux/elf.h>
>  #include <sys/uio.h>
>  #include <sys/utsname.h>
> +#include <sys/fcntl.h>
> +#include <sys/mman.h>
> +#include <sys/times.h>
>
>  #define _GNU_SOURCE
>  #include <unistd.h>
> @@ -429,14 +432,16 @@ TEST_SIGNAL(KILL_one, SIGSYS)
>
>  TEST_SIGNAL(KILL_one_arg_one, SIGSYS)
>  {
> +       void *fatal_address;
>         struct sock_filter filter[] = {
>                 BPF_STMT(BPF_LD|BPF_W|BPF_ABS,
>                         offsetof(struct seccomp_data, nr)),
> -               BPF_JUMP(BPF_JMP|BPF_JEQ|BPF_K, __NR_getpid, 1, 0),
> +               BPF_JUMP(BPF_JMP|BPF_JEQ|BPF_K, __NR_times, 1, 0),
>                 BPF_STMT(BPF_RET|BPF_K, SECCOMP_RET_ALLOW),
>                 /* Only both with lower 32-bit for now. */
>                 BPF_STMT(BPF_LD|BPF_W|BPF_ABS, syscall_arg(0)),
> -               BPF_JUMP(BPF_JMP|BPF_JEQ|BPF_K, 0x0C0FFEE, 0, 1),
> +               BPF_JUMP(BPF_JMP|BPF_JEQ|BPF_K,
> +                       (unsigned long)&fatal_address, 0, 1),
>                 BPF_STMT(BPF_RET|BPF_K, SECCOMP_RET_KILL),
>                 BPF_STMT(BPF_RET|BPF_K, SECCOMP_RET_ALLOW),
>         };
> @@ -446,7 +451,8 @@ TEST_SIGNAL(KILL_one_arg_one, SIGSYS)
>         };
>         long ret;
>         pid_t parent = getppid();
> -       pid_t pid = getpid();
> +       struct tms timebuf;
> +       clock_t clock = times(&timebuf);
>
>         ret = prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0);
>         ASSERT_EQ(0, ret);
> @@ -455,17 +461,22 @@ TEST_SIGNAL(KILL_one_arg_one, SIGSYS)
>         ASSERT_EQ(0, ret);
>
>         EXPECT_EQ(parent, syscall(__NR_getppid));
> -       EXPECT_EQ(pid, syscall(__NR_getpid));
> -       /* getpid() should never return. */
> -       EXPECT_EQ(0, syscall(__NR_getpid, 0x0C0FFEE));
> +       EXPECT_LE(clock, syscall(__NR_times, &timebuf));
> +       /* times() should never return. */
> +       EXPECT_EQ(0, syscall(__NR_times, &fatal_address));
>  }
>
>  TEST_SIGNAL(KILL_one_arg_six, SIGSYS)
>  {
> +#ifndef __NR_mmap2
> +       int sysno = __NR_mmap;
> +#else
> +       int sysno = __NR_mmap2;
> +#endif
>         struct sock_filter filter[] = {
>                 BPF_STMT(BPF_LD|BPF_W|BPF_ABS,
>                         offsetof(struct seccomp_data, nr)),
> -               BPF_JUMP(BPF_JMP|BPF_JEQ|BPF_K, __NR_getpid, 1, 0),
> +               BPF_JUMP(BPF_JMP|BPF_JEQ|BPF_K, sysno, 1, 0),
>                 BPF_STMT(BPF_RET|BPF_K, SECCOMP_RET_ALLOW),
>                 /* Only both with lower 32-bit for now. */
>                 BPF_STMT(BPF_LD|BPF_W|BPF_ABS, syscall_arg(5)),
> @@ -479,7 +490,8 @@ TEST_SIGNAL(KILL_one_arg_six, SIGSYS)
>         };
>         long ret;
>         pid_t parent = getppid();
> -       pid_t pid = getpid();
> +       int fd;
> +       void *map1, *map2;
>
>         ret = prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0);
>         ASSERT_EQ(0, ret);
> @@ -487,10 +499,22 @@ TEST_SIGNAL(KILL_one_arg_six, SIGSYS)
>         ret = prctl(PR_SET_SECCOMP, SECCOMP_MODE_FILTER, &prog);
>         ASSERT_EQ(0, ret);
>
> +       fd = open("/dev/zero", O_RDONLY);
> +       ASSERT_NE(-1, fd);
> +
>         EXPECT_EQ(parent, syscall(__NR_getppid));
> -       EXPECT_EQ(pid, syscall(__NR_getpid));
> -       /* getpid() should never return. */
> -       EXPECT_EQ(0, syscall(__NR_getpid, 1, 2, 3, 4, 5, 0x0C0FFEE));
> +       map1 = (void *)syscall(sysno,
> +               NULL, PAGE_SIZE, PROT_READ, MAP_PRIVATE, fd, PAGE_SIZE);
> +       EXPECT_NE(MAP_FAILED, map1);
> +       /* mmap2() should never return. */
> +       map2 = (void *)syscall(sysno,
> +                NULL, PAGE_SIZE, PROT_READ, MAP_PRIVATE, fd, 0x0C0FFEE);
> +       EXPECT_EQ(MAP_FAILED, map2);
> +
> +       /* The test failed, so clean up the resources. */
> +       munmap(map1, PAGE_SIZE);
> +       munmap(map2, PAGE_SIZE);
> +       close(fd);
>  }
>
>  /* TODO(wad) add 64-bit versus 32-bit arg tests. */
> --
> 2.6.0.rc2.230.g3dd15c0
>



-- 
Kees Cook
Chrome OS Security
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