Commit 0b3b9ca3 authored by Quentin Monnet's avatar Quentin Monnet Committed by Daniel Borkmann

tools: bpftool: Make libcap dependency optional

The new libcap dependency is not used for an essential feature of
bpftool, and we could imagine building the tool without checks on
CAP_SYS_ADMIN by disabling probing features as an unprivileged users.

Make it so, in order to avoid a hard dependency on libcap, and to ease
packaging/embedding of bpftool.
Signed-off-by: default avatarQuentin Monnet <quentin@isovalent.com>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Acked-by: default avatarJohn Fastabend <john.fastabend@gmail.com>
Link: https://lore.kernel.org/bpf/20200429144506.8999-4-quentin@isovalent.com
parent cf9bf714
......@@ -55,7 +55,9 @@ DESCRIPTION
that case usually represent a small subset of the parameters
supported by the system. Unprivileged users MUST use the
**unprivileged** keyword: This is to avoid misdetection if
bpftool is inadvertently run as non-root, for example.
bpftool is inadvertently run as non-root, for example. This
keyword is unavailable if bpftool was compiled without
libcap.
**bpftool feature probe dev** *NAME* [**full**] [**macros** [**prefix** *PREFIX*]]
Probe network device for supported eBPF features and dump
......
......@@ -55,16 +55,15 @@ ifneq ($(EXTRA_LDFLAGS),)
LDFLAGS += $(EXTRA_LDFLAGS)
endif
LIBS = $(LIBBPF) -lelf -lz -lcap
INSTALL ?= install
RM ?= rm -f
CLANG ?= clang
FEATURE_USER = .bpftool
FEATURE_TESTS = libbfd disassembler-four-args reallocarray zlib \
FEATURE_TESTS = libbfd disassembler-four-args reallocarray zlib libcap \
clang-bpf-global-var
FEATURE_DISPLAY = libbfd disassembler-four-args zlib libcap \
clang-bpf-global-var
FEATURE_DISPLAY = libbfd disassembler-four-args zlib clang-bpf-global-var
check_feat := 1
NON_CHECK_FEAT_TARGETS := clean uninstall doc doc-clean doc-install doc-uninstall
......@@ -90,6 +89,12 @@ ifeq ($(feature-reallocarray), 0)
CFLAGS += -DCOMPAT_NEED_REALLOCARRAY
endif
LIBS = $(LIBBPF) -lelf -lz
ifeq ($(feature-libcap), 1)
CFLAGS += -DUSE_LIBCAP
LIBS += -lcap
endif
include $(wildcard $(OUTPUT)*.d)
all: $(OUTPUT)bpftool
......
......@@ -6,7 +6,9 @@
#include <string.h>
#include <unistd.h>
#include <net/if.h>
#ifdef USE_LIBCAP
#include <sys/capability.h>
#endif
#include <sys/utsname.h>
#include <sys/vfs.h>
......@@ -37,7 +39,9 @@ static const char * const helper_name[] = {
#undef BPF_HELPER_MAKE_ENTRY
static bool full_mode;
#ifdef USE_LIBCAP
static bool run_as_unprivileged;
#endif
/* Miscellaneous utility functions */
......@@ -475,11 +479,13 @@ probe_prog_type(enum bpf_prog_type prog_type, bool *supported_types,
}
res = bpf_probe_prog_type(prog_type, ifindex);
#ifdef USE_LIBCAP
/* Probe may succeed even if program load fails, for unprivileged users
* check that we did not fail because of insufficient permissions
*/
if (run_as_unprivileged && errno == EPERM)
res = false;
#endif
supported_types[prog_type] |= res;
......@@ -535,12 +541,14 @@ probe_helper_for_progtype(enum bpf_prog_type prog_type, bool supported_type,
if (supported_type) {
res = bpf_probe_helper(id, prog_type, ifindex);
#ifdef USE_LIBCAP
/* Probe may succeed even if program load fails, for
* unprivileged users check that we did not fail because of
* insufficient permissions
*/
if (run_as_unprivileged && errno == EPERM)
res = false;
#endif
}
if (json_output) {
......@@ -738,6 +746,7 @@ static void section_misc(const char *define_prefix, __u32 ifindex)
static int handle_perms(void)
{
#ifdef USE_LIBCAP
cap_value_t cap_list[1] = { CAP_SYS_ADMIN };
bool has_sys_admin_cap = false;
cap_flag_value_t val;
......@@ -793,6 +802,18 @@ static int handle_perms(void)
}
return res;
#else
/* Detection assumes user has sufficient privileges (CAP_SYS_ADMIN).
* We do not use libpcap so let's approximate, and restrict usage to
* root user only.
*/
if (geteuid()) {
p_err("full feature probing requires root privileges");
return -1;
}
return 0;
#endif /* USE_LIBCAP */
}
static int do_probe(int argc, char **argv)
......@@ -852,8 +873,13 @@ static int do_probe(int argc, char **argv)
return -1;
define_prefix = GET_ARG();
} else if (is_prefix(*argv, "unprivileged")) {
#ifdef USE_LIBCAP
run_as_unprivileged = true;
NEXT_ARG();
#else
p_err("unprivileged run not supported, recompile bpftool with libcap");
return -1;
#endif
} else {
p_err("expected no more arguments, 'kernel', 'dev', 'macros' or 'prefix', got: '%s'?",
*argv);
......
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