bpf/selftests: Test bpf_d_path on rdonly_mem.

The second parameter of bpf_d_path() can only accept writable
memories. Rdonly_mem obtained from bpf_per_cpu_ptr() can not
be passed into bpf_d_path for modification. This patch adds
a selftest to verify this behavior.

Signed-off-by: Hao Luo <haoluo@google.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20220106205525.2116218-1-haoluo@google.com

diff --git a/tools/testing/selftests/bpf/prog_tests/d_path.c b/tools/testing/selftests/bpf/prog_tests/d_path.c
index 0a577a2..32fc5b3 100644 (file)
--- a/tools/testing/selftests/bpf/prog_tests/d_path.c
+++ b/tools/testing/selftests/bpf/prog_tests/d_path.c
@@ -9,6 +9,7 @@
 #define MAX_FILES              7
 
 #include "test_d_path.skel.h"
+#include "test_d_path_check_rdonly_mem.skel.h"
 
 static int duration;
 
@@ -99,7 +100,7 @@ out_close:
        return ret;
 }
 
-void test_d_path(void)
+static void test_d_path_basic(void)
 {
        struct test_d_path__bss *bss;
        struct test_d_path *skel;
@@ -155,3 +156,22 @@ void test_d_path(void)
 cleanup:
        test_d_path__destroy(skel);
 }
+
+static void test_d_path_check_rdonly_mem(void)
+{
+       struct test_d_path_check_rdonly_mem *skel;
+
+       skel = test_d_path_check_rdonly_mem__open_and_load();
+       ASSERT_ERR_PTR(skel, "unexpected_load_overwriting_rdonly_mem");
+
+       test_d_path_check_rdonly_mem__destroy(skel);
+}
+
+void test_d_path(void)
+{
+       if (test__start_subtest("basic"))
+               test_d_path_basic();
+
+       if (test__start_subtest("check_rdonly_mem"))
+               test_d_path_check_rdonly_mem();
+}

diff --git a/tools/testing/selftests/bpf/progs/test_d_path_check_rdonly_mem.c b/tools/testing/selftests/bpf/progs/test_d_path_check_rdonly_mem.c
new file mode 100644 (file)
index 0000000..27c27cf
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/test_d_path_check_rdonly_mem.c
@@ -0,0 +1,28 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2022 Google */
+
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+
+extern const int bpf_prog_active __ksym;
+
+SEC("fentry/security_inode_getattr")
+int BPF_PROG(d_path_check_rdonly_mem, struct path *path, struct kstat *stat,
+            __u32 request_mask, unsigned int query_flags)
+{
+       void *active;
+       __u32 cpu;
+
+       cpu = bpf_get_smp_processor_id();
+       active = (void *)bpf_per_cpu_ptr(&bpf_prog_active, cpu);
+       if (active) {
+               /* FAIL here! 'active' points to readonly memory. bpf helpers
+                * that update its arguments can not write into it.
+                */
+               bpf_d_path(path, active, sizeof(int));
+       }
+       return 0;
+}
+
+char _license[] SEC("license") = "GPL";