Re: [PATCH bpf-next v4 8/9] bpf: Add tests for task_local_storage

[Martin KaFai Lau]

On Thu, Nov 05, 2020 at 03:47:54PM +0100, KP Singh wrote:
> From: KP Singh <kpsingh@xxxxxxxxxx>
> 
> The test exercises the syscall based map operations by creating a pidfd
> for the current process.
> 
> For verifying kernel / LSM functionality, the test implements a simple
> MAC policy which denies an executable from unlinking itself. The LSM
> program bprm_committed_creds sets a task_local_storage with a pointer to
> the inode. This is then used to detect if the task is trying to unlink
> itself in the inode_unlink LSM hook.
> 
> The test copies /bin/rm to /tmp and executes it in a child thread with
> the intention of deleting itself. A successful test should prevent the
> the running executable from deleting itself.
> 
> The bpf programs are also updated to call bpf_spin_{lock, unlock} to
> trigger the verfier checks for spin locks.
> 
> The temporary file is cleaned up later in the test.
> 
> Signed-off-by: KP Singh <kpsingh@xxxxxxxxxx>
> ---
>  .../bpf/prog_tests/test_local_storage.c       | 167 ++++++++++++++++--
>  .../selftests/bpf/progs/local_storage.c       |  61 ++++++-
>  2 files changed, 210 insertions(+), 18 deletions(-)
> 
> diff --git a/tools/testing/selftests/bpf/prog_tests/test_local_storage.c b/tools/testing/selftests/bpf/prog_tests/test_local_storage.c
> index 91cd6f357246..feba23f8848b 100644
> --- a/tools/testing/selftests/bpf/prog_tests/test_local_storage.c
> +++ b/tools/testing/selftests/bpf/prog_tests/test_local_storage.c
> @@ -4,30 +4,149 @@
>   * Copyright (C) 2020 Google LLC.
>   */
>  
> +#define _GNU_SOURCE
> +
> +#include <asm-generic/errno-base.h>
> +#include <unistd.h>
> +#include <sys/stat.h>
>  #include <test_progs.h>
>  #include <linux/limits.h>
>  
>  #include "local_storage.skel.h"
>  #include "network_helpers.h"
>  
> -int create_and_unlink_file(void)
> +static inline int sys_pidfd_open(pid_t pid, unsigned int flags)
> +{
> +	return syscall(__NR_pidfd_open, pid, flags);
> +}
> +
> +unsigned int duration;
static

> +
> +#define TEST_STORAGE_VALUE 0xbeefdead
> +
> +struct storage {
> +	void *inode;
> +	unsigned int value;
> +	/* Lock ensures that spin locked versions of local stoage operations
> +	 * also work, most operations in this tests are still single threaded
> +	 */
> +	struct bpf_spin_lock lock;
> +};
> +
> +/* Copies an rm binary to a temp file. dest is a mkstemp template */
> +int copy_rm(char *dest)
static

>  {
> -	char fname[PATH_MAX] = "/tmp/fileXXXXXX";
> -	int fd;
> +	int ret, fd_in, fd_out;
> +	struct stat stat;
>  
> -	fd = mkstemp(fname);
> -	if (fd < 0)
> -		return fd;
> +	fd_in = open("/bin/rm", O_RDONLY);
> +	if (fd_in < 0)
> +		return fd_in;
>  
> -	close(fd);
> -	unlink(fname);
> +	fd_out = mkstemp(dest);
> +	if (fd_out < 0)
> +		return fd_out;
> +
> +	ret = fstat(fd_in, &stat);
> +	if (ret == -1)
> +		return errno;
> +
> +	ret = copy_file_range(fd_in, NULL, fd_out, NULL, stat.st_size, 0);
> +	if (ret == -1)
> +		return errno;
> +
> +	/* Set executable permission on the copied file */
> +	ret = chmod(dest, 0100);
> +	if (ret == -1)
> +		return errno;
> +
> +	close(fd_in);
> +	close(fd_out);
fd_in and fd_out are not closed in error cases.

>  	return 0;
>  }
>  
> +/* Fork and exec the provided rm binary and return the exit code of the
> + * forked process and its pid.
> + */
> +int run_self_unlink(int *monitored_pid, const char *rm_path)
static

[ ... ]

> +bool check_syscall_operations(int map_fd, int obj_fd)
static

[ ... ]

>  void test_test_local_storage(void)
>  {
> +	char tmp_exec_path[PATH_MAX] = "/tmp/copy_of_rmXXXXXX";
> +	int err, serv_sk = -1, task_fd = -1;
>  	struct local_storage *skel = NULL;
> -	int err, duration = 0, serv_sk = -1;
>  
>  	skel = local_storage__open_and_load();
>  	if (CHECK(!skel, "skel_load", "lsm skeleton failed\n"))
> @@ -37,10 +156,35 @@ void test_test_local_storage(void)
>  	if (CHECK(err, "attach", "lsm attach failed: %d\n", err))
>  		goto close_prog;
>  
> +	task_fd = sys_pidfd_open(getpid(), 0);
> +	if (CHECK(task_fd < 0, "pidfd_open",
> +		  "failed to get pidfd err:%d, errno:%d", task_fd, errno))
> +		goto close_prog;
> +
> +	if (!check_syscall_operations(bpf_map__fd(skel->maps.task_storage_map),
> +				      task_fd))
> +		goto close_prog;
> +
> +	err = copy_rm(tmp_exec_path);
> +	if (CHECK(err < 0, "copy_rm", "err %d errno %d\n", err, errno))
> +		goto close_prog;
> +
> +	/* Sets skel->bss->monitored_pid to the pid of the forked child
> +	 * forks a child process that executes tmp_exec_path and tries to
> +	 * unlink its executable. This operation should be denied by the loaded
> +	 * LSM program.
> +	 */
> +	err = run_self_unlink(&skel->bss->monitored_pid, tmp_exec_path);
> +	if (CHECK(err != EPERM, "run_self_unlink", "err %d want EPERM\n", err))
> +		goto close_prog;
> +
> +	/* Set the process being monitored to be the current process */
>  	skel->bss->monitored_pid = getpid();
>  
> -	err = create_and_unlink_file();
> -	if (CHECK(err < 0, "exec_cmd", "err %d errno %d\n", err, errno))
> +	/* Remove the temporary created executable */
> +	err = unlink(tmp_exec_path);
Will tmp_exec_path file be removed if there is error earlier?

> +	if (CHECK(err != 0, "unlink", "unable to unlink %s: %d", tmp_exec_path,
> +		  errno))
>  		goto close_prog;
>  
>  	CHECK(skel->data->inode_storage_result != 0, "inode_storage_result",
> @@ -56,5 +200,6 @@ void test_test_local_storage(void)
>  	close(serv_sk);
>  
>  close_prog:
> +	close(task_fd);
>  	local_storage__destroy(skel);
>  }