netdev - [PATCH bpf-next] selftests/bpf: Fix stat probe in d

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Date:   Wed, 16 Sep 2020 13:24:16 +0200
From:   Jiri Olsa <jolsa@...nel.org>
To:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andriin@...com>
Cc:     netdev@...r.kernel.org, bpf@...r.kernel.org,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>
Subject: [PATCH bpf-next] selftests/bpf: Fix stat probe in d_path test

Some kernels builds might inline vfs_getattr call within fstat
syscall code path, so fentry/vfs_getattr trampoline is not called.

Alexei suggested [1] we should use security_inode_getattr instead,
because it's less likely to get inlined.

Adding security_inode_getattr to the d_path allowed list and
switching the stat trampoline to security_inode_getattr.

Adding flags that indicate trampolines were called and failing
the test if any of them got missed, so it's easier to identify
the issue next time.

[1] https://lore.kernel.org/bpf/CAADnVQJ0FchoPqNWm+dEppyij-MOvvEG_trEfyrHdabtcEuZGg@mail.gmail.com/
Fixes: e4d1af4b16f8 ("selftests/bpf: Add test for d_path helper")
Signed-off-by: Jiri Olsa <jolsa@...hat.com>
---
 kernel/trace/bpf_trace.c                        | 1 +
 tools/testing/selftests/bpf/prog_tests/d_path.c | 6 ++++++
 tools/testing/selftests/bpf/progs/test_d_path.c | 9 ++++++++-
 3 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index b2a5380eb187..1001c053ebb3 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -1122,6 +1122,7 @@ BTF_ID(func, vfs_truncate)
 BTF_ID(func, vfs_fallocate)
 BTF_ID(func, dentry_open)
 BTF_ID(func, vfs_getattr)
+BTF_ID(func, security_inode_getattr)
 BTF_ID(func, filp_close)
 BTF_SET_END(btf_allowlist_d_path)
 
diff --git a/tools/testing/selftests/bpf/prog_tests/d_path.c b/tools/testing/selftests/bpf/prog_tests/d_path.c
index fc12e0d445ff..f507f1a6fa3a 100644
--- a/tools/testing/selftests/bpf/prog_tests/d_path.c
+++ b/tools/testing/selftests/bpf/prog_tests/d_path.c
@@ -120,6 +120,12 @@ void test_d_path(void)
 	if (err < 0)
 		goto cleanup;
 
+	if (CHECK(!bss->called_stat || !bss->called_close,
+		  "check",
+		  "failed to call trampolines called_stat %d, bss->called_close %d\n",
+		   bss->called_stat, bss->called_close))
+		goto cleanup;
+
 	for (int i = 0; i < MAX_FILES; i++) {
 		CHECK(strncmp(src.paths[i], bss->paths_stat[i], MAX_PATH_LEN),
 		      "check",
diff --git a/tools/testing/selftests/bpf/progs/test_d_path.c b/tools/testing/selftests/bpf/progs/test_d_path.c
index 61f007855649..84e1f883f97b 100644
--- a/tools/testing/selftests/bpf/progs/test_d_path.c
+++ b/tools/testing/selftests/bpf/progs/test_d_path.c
@@ -15,7 +15,10 @@ char paths_close[MAX_FILES][MAX_PATH_LEN] = {};
 int rets_stat[MAX_FILES] = {};
 int rets_close[MAX_FILES] = {};
 
-SEC("fentry/vfs_getattr")
+int called_stat = 0;
+int called_close = 0;
+
+SEC("fentry/security_inode_getattr")
 int BPF_PROG(prog_stat, struct path *path, struct kstat *stat,
 	     __u32 request_mask, unsigned int query_flags)
 {
@@ -23,6 +26,8 @@ int BPF_PROG(prog_stat, struct path *path, struct kstat *stat,
 	__u32 cnt = cnt_stat;
 	int ret;
 
+	called_stat = 1;
+
 	if (pid != my_pid)
 		return 0;
 
@@ -42,6 +47,8 @@ int BPF_PROG(prog_close, struct file *file, void *id)
 	__u32 cnt = cnt_close;
 	int ret;
 
+	called_close = 1;
+
 	if (pid != my_pid)
 		return 0;
 
-- 
2.26.2