[PATCH bpf-next 3/4] libbpf: add libbpf_[get|put]_bpf_permission()

[Song Liu <songliubraving@xxxxxx>]

This patch adds two more API to libbpf: libbpf_get_bpf_permission() and
libbpf_put_bpf_permission().

For root, these two APIs are no-op.

Signed-off-by: Song Liu <songliubraving@xxxxxx>
---
 tools/lib/bpf/libbpf.c   | 54 ++++++++++++++++++++++++++++++++++++++++
 tools/lib/bpf/libbpf.h   |  7 ++++++
 tools/lib/bpf/libbpf.map |  2 ++
 3 files changed, 63 insertions(+)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 68f45a96769f..cf2d68268bde 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -35,6 +35,7 @@
 #include <sys/stat.h>
 #include <sys/types.h>
 #include <sys/vfs.h>
+#include <sys/ioctl.h>
 #include <tools/libc_compat.h>
 #include <libelf.h>
 #include <gelf.h>
@@ -4286,3 +4287,56 @@ int libbpf_num_possible_cpus(void)
 	}
 	return cpus;
 }
+
+LIBBPF_API bool libbpf_get_bpf_permission(void)
+{
+	char *cp, errmsg[STRERR_BUFSIZE];
+	int fd, ret;
+
+	if (geteuid() == 0)
+		return true;
+
+	fd = open(LIBBPF_DEV_BPF, O_RDONLY);
+	if (fd < 0) {
+		cp = libbpf_strerror_r(errno, errmsg, sizeof(errmsg));
+		pr_warning("failed to open %s: %s\n", LIBBPF_DEV_BPF, cp);
+		return false;
+	}
+
+	ret = ioctl(fd, BPF_DEV_IOCTL_GET_PERM);
+
+	if (ret) {
+		cp = libbpf_strerror_r(errno, errmsg, sizeof(errmsg));
+		pr_warning("failed to get BPF permission: %s\n", cp);
+		close(fd);
+		return false;
+	}
+	close(fd);
+	pr_debug("got BPF permission for non-privileged user\n");
+	return true;
+}
+
+LIBBPF_API void libbpf_put_bpf_permission(void)
+{
+	char *cp, errmsg[STRERR_BUFSIZE];
+	int fd, ret;
+
+	if (geteuid() == 0)
+		return;
+
+	fd = open(LIBBPF_DEV_BPF, O_RDONLY);
+	if (fd < 0) {
+		cp = libbpf_strerror_r(errno, errmsg, sizeof(errmsg));
+		pr_warning("failed to open %s: %s\n", LIBBPF_DEV_BPF, cp);
+		return;
+	}
+
+	ret = ioctl(fd, BPF_DEV_IOCTL_PUT_PERM);
+	if (ret) {
+		cp = libbpf_strerror_r(errno, errmsg, sizeof(errmsg));
+		pr_warning("failed to release BPF permission: %s\n", cp);
+		close(fd);
+	}
+	close(fd);
+	pr_debug("released BPF permission for non-privileged user\n");
+}
diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
index d639f47e3110..22052c55a96c 100644
--- a/tools/lib/bpf/libbpf.h
+++ b/tools/lib/bpf/libbpf.h
@@ -470,6 +470,13 @@ bpf_program__bpil_offs_to_addr(struct bpf_prog_info_linear *info_linear);
  */
 LIBBPF_API int libbpf_num_possible_cpus(void);
 
+#define LIBBPF_DEV_BPF "/dev/bpf"
+
+/* (For non-root user) get permission to access bpf() syscall */
+LIBBPF_API bool libbpf_get_bpf_permission(void);
+/* (For non-root user) put permission to access bpf() syscall */
+LIBBPF_API void libbpf_put_bpf_permission(void);
+
 #ifdef __cplusplus
 } /* extern "C" */
 #endif
diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
index 2c6d835620d2..93a2c4175fdd 100644
--- a/tools/lib/bpf/libbpf.map
+++ b/tools/lib/bpf/libbpf.map
@@ -173,4 +173,6 @@ LIBBPF_0.0.4 {
 		btf__parse_elf;
 		bpf_object__load_xattr;
 		libbpf_num_possible_cpus;
+		libbpf_get_bpf_permission;
+		libbpf_put_bpf_permission;
 } LIBBPF_0.0.3;
-- 
2.17.1