setpriv: dump inheritable capability set

The setpriv executable from util-linux also dumps out information on the
different capability sets known by the kernel. By default, these are the
inheritable capabilities, bounding capabilities and (not yet released)
the ambient capabilities, which have been introduced with Linux 4.3.
This patch introduces the ability to dump the set of inheritable
capabilities.

By default, setpriv(1) identifies capabilities by their human-readable
name, for example 'net_admin'. For unknown capabilities, though, it does
instead use the capability's value, for example 'cap_12', which is
equivalent to 'net_admin'. As there is no kernel interface to retrieve
capability names by their index, we have to declare these ourselves,
which adds to setpriv's size.

To counteract, using the human-readble name has been made configurable.
The following sizes are with the 'FEATURE_SETPRIV_CAPABILITY_NAMES'
enabled:

function                                             old     new   delta
.rodata                                           145969  146405    +436
setpriv_main                                         467     842    +375
capabilities                                           -     304    +304

And with 'FEATURE_SETPRIV_CAPABILITY_NAMES' disabled:

function                                             old     new   delta
setpriv_main                                         467     838    +371
.rodata                                           145969  146101    +132

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 147 insertions, 4 deletions

diff --git a/util-linux/setpriv.c b/util-linux/setpriv.c
index 8d3f258..a509204 100644
--- a/util-linux/setpriv.c
+++ b/util-linux/setpriv.c
@@ -23,6 +23,26 @@
 //config:	help
 //config:	  Enables the "--dump" switch to print out the current privilege
 //config:	  state. This is helpful for diagnosing problems.
+//config:
+//config:config FEATURE_SETPRIV_CAPABILITIES
+//config:	bool "Support capabilities"
+//config:	default y
+//config:	depends on SETPRIV
+//config:	help
+//config:	  Capabilities can be used to grant processes additional rights
+//config:	  without the necessity to always execute as the root user.
+//config:	  Enabling this option enables "--dump" to show information on
+//config:	  capabilities.
+//config:
+//config:config FEATURE_SETPRIV_CAPABILITY_NAMES
+//config:	bool "Support capability names"
+//config:	default y
+//config:	depends on SETPRIV && FEATURE_SETPRIV_CAPABILITIES
+//config:	help
+//config:	  Capabilities can be either referenced via a human-readble name,
+//config:	  e.g. "net_admin", or using their index, e.g. "cap_12". Enabling
+//config:	  this option allows using the human-readable names in addition to
+//config:	  the index-based names.
 
 //applet:IF_SETPRIV(APPLET(setpriv, BB_DIR_BIN, BB_SUID_DROP))
 
@@ -55,6 +75,10 @@
 // --selinux-label <label>  set SELinux label
 // --apparmor-profile <pr>  set AppArmor profile
 
+#if ENABLE_FEATURE_SETPRIV_CAPABILITIES
+#include <linux/capability.h>
+#include <sys/capability.h>
+#endif
 #include <sys/prctl.h>
 #include "libbb.h"
 
@@ -74,13 +98,106 @@ enum {
 	OPT_NNP  = (1 << OPTBIT_NNP),
 };
 
+#if ENABLE_FEATURE_SETPRIV_CAPABILITIES
+struct caps {
+	struct __user_cap_header_struct header;
+	cap_user_data_t data;
+	int u32s;
+};
+
+#if ENABLE_FEATURE_SETPRIV_CAPABILITY_NAMES
+static const char *const capabilities[] = {
+	"chown",
+	"dac_override",
+	"dac_read_search",
+	"fowner",
+	"fsetid",
+	"kill",
+	"setgid",
+	"setuid",
+	"setpcap",
+	"linux_immutable",
+	"net_bind_service",
+	"net_broadcast",
+	"net_admin",
+	"net_raw",
+	"ipc_lock",
+	"ipc_owner",
+	"sys_module",
+	"sys_rawio",
+	"sys_chroot",
+	"sys_ptrace",
+	"sys_pacct",
+	"sys_admin",
+	"sys_boot",
+	"sys_nice",
+	"sys_resource",
+	"sys_time",
+	"sys_tty_config",
+	"mknod",
+	"lease",
+	"audit_write",
+	"audit_control",
+	"setfcap",
+	"mac_override",
+	"mac_admin",
+	"syslog",
+	"wake_alarm",
+	"block_suspend",
+	"audit_read",
+};
+#endif /* FEATURE_SETPRIV_CAPABILITY_NAMES */
+
+#endif /* FEATURE_SETPRIV_CAPABILITIES */
+
 #if ENABLE_FEATURE_SETPRIV_DUMP
+# if ENABLE_FEATURE_SETPRIV_CAPABILITIES
+static void getcaps(struct caps *caps)
+{
+	int versions[] = {
+		_LINUX_CAPABILITY_U32S_3,
+		_LINUX_CAPABILITY_U32S_2,
+		_LINUX_CAPABILITY_U32S_1,
+	};
+	int i;
+
+	caps->header.pid = 0;
+	for (i = 0; i < ARRAY_SIZE(versions); i++) {
+		caps->header.version = versions[i];
+		if (capget(&caps->header, NULL) == 0)
+			goto got_it;
+	}
+	bb_simple_perror_msg_and_die("capget");
+ got_it:
+
+	switch (caps->header.version) {
+		case _LINUX_CAPABILITY_VERSION_1:
+			caps->u32s = _LINUX_CAPABILITY_U32S_1;
+			break;
+		case _LINUX_CAPABILITY_VERSION_2:
+			caps->u32s = _LINUX_CAPABILITY_U32S_2;
+			break;
+		case _LINUX_CAPABILITY_VERSION_3:
+			caps->u32s = _LINUX_CAPABILITY_U32S_3;
+			break;
+		default:
+			bb_error_msg_and_die("unsupported capability version");
+	}
+
+	caps->data = xmalloc(sizeof(caps->data[0]) * caps->u32s);
+	if (capget(&caps->header, caps->data) < 0)
+		bb_simple_perror_msg_and_die("capget");
+}
+# endif /* FEATURE_SETPRIV_CAPABILITIES */
+
 static int dump(void)
 {
+	IF_FEATURE_SETPRIV_CAPABILITIES(struct caps caps;)
+	const char *fmt;
 	uid_t ruid, euid, suid;
 	gid_t rgid, egid, sgid;
 	gid_t *gids;
-	int ngids, nnp;
+	int i, ngids, nnp;
 
 	getresuid(&ruid, &euid, &suid); /* never fails in Linux */
 	getresgid(&rgid, &egid, &sgid); /* never fails in Linux */
@@ -100,8 +217,7 @@ static int dump(void)
 	if (ngids == 0) {
 		printf("[none]");
 	} else {
-		const char *fmt = ",%u" + 1;
-		int i;
+		fmt = ",%u" + 1;
 		for (i = 0; i < ngids; i++) {
 			printf(fmt, (unsigned)gids[i]);
 			fmt = ",%u";
@@ -109,8 +225,35 @@ static int dump(void)
 	}
 	printf("\nno_new_privs: %d\n", nnp);
 
-	if (ENABLE_FEATURE_CLEAN_UP)
+# if ENABLE_FEATURE_SETPRIV_CAPABILITIES
+	getcaps(&caps);
+	printf("Inheritable capabilities: ");
+	fmt = "";
+	for (i = 0; cap_valid(i); i++) {
+		unsigned idx = CAP_TO_INDEX(i);
+		if (idx >= caps.u32s) {
+			printf("\nindex: %u u32s: %u capability: %u\n", idx, caps.u32s, i);
+			bb_error_msg_and_die("unsupported capability");
+		}
+		if (caps.data[idx].inheritable & CAP_TO_MASK(i)) {
+#  if ENABLE_FEATURE_SETPRIV_CAPABILITY_NAMES
+			if (i < ARRAY_SIZE(capabilities))
+				printf("%s%s", fmt, capabilities[i]);
+			else
+#  endif
+				printf("%scap_%u", fmt, i);
+			fmt = ",";
+		}
+	}
+	if (!fmt[0])
+		printf("[none]");
+	bb_putchar('\n');
+# endif
+
+	if (ENABLE_FEATURE_CLEAN_UP) {
+		IF_FEATURE_SETPRIV_CAPABILITIES(free(caps.data);)
 		free(gids);
+	}
 	return EXIT_SUCCESS;
 }
 #endif /* FEATURE_SETPRIV_DUMP */