Re: [PATCH bpf v2 1/3] bpf: update local storage test to check handling of null ptrs

[Yonghong Song <yhs@fb.com>]

On 1/11/21 1:23 PM, KP Singh wrote:
> It was found in [1] that bpf_inode_storage_get helper did not check
> the nullness of the passed owner ptr which caused an oops when
> dereferenced. This change incorporates the example suggested in [1] into
> the local storage selftest.
> 
> The test is updated to create a temporary directory instead of just
> using a tempfile. In order to replicate the issue this copied rm binary
> is renamed tiggering the inode_rename with a null pointer for the
> new_inode. The logic to verify the setting and deletion of the inode
> local storage of the old inode is also moved to this LSM hook.
> 
> The change also removes the copy_rm function and simply shells out
> to copy files and recursively delete directories and consolidates the
> logic of setting the initial inode storage to the bprm_committed_creds
> hook and removes the file_open hook.
> 
> [1]: https://lore.kernel.org/bpf/CANaYP3HWkH91SN=wTNO9FL_2ztHfqcXKX38SSE-JJ2voh+vssw@mail.gmail.com
> 
> Suggested-by: Gilad Reti <gilad.reti@gmail.com>
> Signed-off-by: KP Singh <kpsingh@kernel.org>

Ack with one nit below.

Acked-by: Yonghong Song <yhs@fb.com>

> ---
>   .../bpf/prog_tests/test_local_storage.c       | 96 +++++--------------
>   .../selftests/bpf/progs/local_storage.c       | 62 ++++++------
>   2 files changed, 61 insertions(+), 97 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 c0fe73a17ed1..338475fe9ffb 100644
> --- a/tools/testing/selftests/bpf/prog_tests/test_local_storage.c
> +++ b/tools/testing/selftests/bpf/prog_tests/test_local_storage.c
> @@ -34,61 +34,6 @@ struct storage {
>   	struct bpf_spin_lock lock;
>   };
>   
> -/* Copies an rm binary to a temp file. dest is a mkstemp template */
> -static int copy_rm(char *dest)
> -{
> -	int fd_in, fd_out = -1, ret = 0;
> -	struct stat stat;
> -	char *buf = NULL;
> -
> -	fd_in = open("/bin/rm", O_RDONLY);
> -	if (fd_in < 0)
> -		return -errno;
> -
> -	fd_out = mkstemp(dest);
> -	if (fd_out < 0) {
> -		ret = -errno;
> -		goto out;
> -	}
> -
> -	ret = fstat(fd_in, &stat);
> -	if (ret == -1) {
> -		ret = -errno;
> -		goto out;
> -	}
> -
> -	buf = malloc(stat.st_blksize);
> -	if (!buf) {
> -		ret = -errno;
> -		goto out;
> -	}
> -
> -	while (ret = read(fd_in, buf, stat.st_blksize), ret > 0) {
> -		ret = write(fd_out, buf, ret);
> -		if (ret < 0) {
> -			ret = -errno;
> -			goto out;
> -
> -		}
> -	}
> -	if (ret < 0) {
> -		ret = -errno;
> -		goto out;
> -
> -	}
> -
> -	/* Set executable permission on the copied file */
> -	ret = chmod(dest, 0100);
> -	if (ret == -1)
> -		ret = -errno;
> -
> -out:
> -	free(buf);
> -	close(fd_in);
> -	close(fd_out);
> -	return ret;
> -}
> -
>   /* Fork and exec the provided rm binary and return the exit code of the
>    * forked process and its pid.
>    */
> @@ -168,9 +113,11 @@ static bool check_syscall_operations(int map_fd, int obj_fd)
>   
>   void test_test_local_storage(void)
>   {
> -	char tmp_exec_path[PATH_MAX] = "/tmp/copy_of_rmXXXXXX";
> +	char tmp_dir_path[64] = "/tmp/local_storageXXXXXX";
>   	int err, serv_sk = -1, task_fd = -1, rm_fd = -1;
>   	struct local_storage *skel = NULL;
> +	char tmp_exec_path[64];
> +	char cmd[256];
>   
>   	skel = local_storage__open_and_load();
>   	if (CHECK(!skel, "skel_load", "lsm skeleton failed\n"))
> @@ -189,18 +136,24 @@ void test_test_local_storage(void)
>   				      task_fd))
>   		goto close_prog;
>   
> -	err = copy_rm(tmp_exec_path);
> -	if (CHECK(err < 0, "copy_rm", "err %d errno %d\n", err, errno))
> +	mkdtemp(tmp_dir_path);
> +	if (CHECK(errno < 0, "mkdtemp", "unable to create tmpdir: %d\n", errno))

I think checking mkdtemp return value is more reliable than checking 
errno. It is possible mkdtemp returns 0 and errno is not 0 (inheritted 
from previous syscall).

>   		goto close_prog;
>   
> +	snprintf(tmp_exec_path, sizeof(tmp_exec_path), "%s/copy_of_rm",
> +		 tmp_dir_path);
> +	snprintf(cmd, sizeof(cmd), "cp /bin/rm %s", tmp_exec_path);
> +	if (CHECK_FAIL(system(cmd)))
> +		goto close_prog_rmdir;
> +
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