From: Martin KaFai Lau <kafai@fb.com>
Date: Wed, 16 Mar 2022 10:38:23 -0700
Subject: bpf: selftests: Add helpers to directly use the capget and capset
 syscall
Patch-mainline: v5.18-rc1
Git-commit: 663af70aabb7c9b6bd5e1c1cdeb44e7025a4f855
References: jsc#PED-1377

After upgrading to the newer libcap (>= 2.60),
the libcap commit aca076443591 ("Make cap_t operations thread safe.")
added a "__u8 mutex;" to the "struct _cap_struct".  It caused a few byte
shift that breaks the assumption made in the "struct libcap" definition
in test_verifier.c.

The bpf selftest usage only needs to enable and disable the effective
caps of the running task.  It is easier to directly syscall the
capget and capset instead.  It can also remove the libcap
library dependency.

The cap_helpers.{c,h} is added.  One __u64 is used for all CAP_*
bits instead of two __u32.

Signed-off-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Link: https://lore.kernel.org/bpf/20220316173823.2036955-1-kafai@fb.com
Acked-by: Shung-Hsi Yu <shung-hsi.yu@suse.com>
---
 tools/testing/selftests/bpf/cap_helpers.c |   67 ++++++++++++++++++++++++++++++
 tools/testing/selftests/bpf/cap_helpers.h |   19 ++++++++
 2 files changed, 86 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/cap_helpers.c
 create mode 100644 tools/testing/selftests/bpf/cap_helpers.h

--- /dev/null
+++ b/tools/testing/selftests/bpf/cap_helpers.c
@@ -0,0 +1,67 @@
+// SPDX-License-Identifier: GPL-2.0
+#include "cap_helpers.h"
+
+/* Avoid including <sys/capability.h> from the libcap-devel package,
+ * so directly declare them here and use them from glibc.
+ */
+int capget(cap_user_header_t header, cap_user_data_t data);
+int capset(cap_user_header_t header, const cap_user_data_t data);
+
+int cap_enable_effective(__u64 caps, __u64 *old_caps)
+{
+	struct __user_cap_data_struct data[_LINUX_CAPABILITY_U32S_3];
+	struct __user_cap_header_struct hdr = {
+		.version = _LINUX_CAPABILITY_VERSION_3,
+	};
+	__u32 cap0 = caps;
+	__u32 cap1 = caps >> 32;
+	int err;
+
+	err = capget(&hdr, data);
+	if (err)
+		return err;
+
+	if (old_caps)
+		*old_caps = (__u64)(data[1].effective) << 32 | data[0].effective;
+
+	if ((data[0].effective & cap0) == cap0 &&
+	    (data[1].effective & cap1) == cap1)
+		return 0;
+
+	data[0].effective |= cap0;
+	data[1].effective |= cap1;
+	err = capset(&hdr, data);
+	if (err)
+		return err;
+
+	return 0;
+}
+
+int cap_disable_effective(__u64 caps, __u64 *old_caps)
+{
+	struct __user_cap_data_struct data[_LINUX_CAPABILITY_U32S_3];
+	struct __user_cap_header_struct hdr = {
+		.version = _LINUX_CAPABILITY_VERSION_3,
+	};
+	__u32 cap0 = caps;
+	__u32 cap1 = caps >> 32;
+	int err;
+
+	err = capget(&hdr, data);
+	if (err)
+		return err;
+
+	if (old_caps)
+		*old_caps = (__u64)(data[1].effective) << 32 | data[0].effective;
+
+	if (!(data[0].effective & cap0) && !(data[1].effective & cap1))
+		return 0;
+
+	data[0].effective &= ~cap0;
+	data[1].effective &= ~cap1;
+	err = capset(&hdr, data);
+	if (err)
+		return err;
+
+	return 0;
+}
--- /dev/null
+++ b/tools/testing/selftests/bpf/cap_helpers.h
@@ -0,0 +1,19 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __CAP_HELPERS_H
+#define __CAP_HELPERS_H
+
+#include <linux/types.h>
+#include <linux/capability.h>
+
+#ifndef CAP_PERFMON
+#define CAP_PERFMON		38
+#endif
+
+#ifndef CAP_BPF
+#define CAP_BPF			39
+#endif
+
+int cap_enable_effective(__u64 caps, __u64 *old_caps);
+int cap_disable_effective(__u64 caps, __u64 *old_caps);
+
+#endif