[git commit] run-init: new applet
Denys Vlasenko
vda.linux at googlemail.com
Mon Aug 21 17:30:01 UTC 2017
commit: https://git.busybox.net/busybox/commit/?id=200bcc851acbe1ba30fe90b5cf918f88370a5d15
branch: https://git.busybox.net/busybox/commit/?id=refs/heads/master
function old new delta
switch_root_main 354 637 +283
drop_usermodehelper - 157 +157
cap_name_to_number - 77 +77
packed_usage 31707 31743 +36
applet_names 2665 2674 +9
applet_main 1544 1548 +4
applet_install_loc 193 194 +1
setpriv_main 933 928 -5
getcaps 131 122 -9
parse_cap 117 29 -88
------------------------------------------------------------------------------
(add/remove: 3/0 grow/shrink: 5/3 up/down: 567/-102) Total: 465 bytes
Signed-off-by: Denys Vlasenko <vda.linux at googlemail.com>
---
include/libbb.h | 9 ++++
klibc-utils/run-init.c | 27 ++++++++++
libbb/capability.c | 47 ++++++++++++++++++
util-linux/setpriv.c | 55 ++-------------------
util-linux/switch_root.c | 126 ++++++++++++++++++++++++++++++++++++++++++++++-
5 files changed, 212 insertions(+), 52 deletions(-)
diff --git a/include/libbb.h b/include/libbb.h
index 9535f5f..95a7470 100644
--- a/include/libbb.h
+++ b/include/libbb.h
@@ -1475,6 +1475,15 @@ const char *get_shell_name(void) FAST_FUNC;
unsigned cap_name_to_number(const char *cap) FAST_FUNC;
void printf_cap(const char *pfx, unsigned cap_no) FAST_FUNC;
+void drop_capability(int cap_ordinal) FAST_FUNC;
+/* Structures inside "struct caps" are Linux-specific and libcap-specific: */
+#define DEFINE_STRUCT_CAPS \
+struct caps { \
+ struct __user_cap_header_struct header; \
+ unsigned u32s; \
+ struct __user_cap_data_struct data[2]; \
+}
+void getcaps(void *caps) FAST_FUNC;
unsigned cap_name_to_number(const char *name) FAST_FUNC;
void printf_cap(const char *pfx, unsigned cap_no) FAST_FUNC;
diff --git a/klibc-utils/run-init.c b/klibc-utils/run-init.c
new file mode 100644
index 0000000..a70d1bf
--- /dev/null
+++ b/klibc-utils/run-init.c
@@ -0,0 +1,27 @@
+/*
+ * run-init implementation for busybox
+ *
+ * Copyright (c) 2017 Denys Vlasenko <vda.linux at gmail.com>
+ *
+ * Licensed under GPLv2, see file LICENSE in this source tree.
+ */
+//config:config RUN_INIT
+//config: bool "run-init"
+//config: default y
+//config: select PLATFORM_LINUX
+//config: help
+//config: The run-init utility is used from initramfs to select a new
+//config: root device. Under initramfs, you have to use this instead of
+//config: pivot_root.
+//config:
+//config: Booting with initramfs extracts a gzipped cpio archive into rootfs
+//config: (which is a variant of ramfs/tmpfs). Because rootfs can't be moved
+//config: or unmounted, pivot_root will not work from initramfs. Instead,
+//config: run-init deletes everything out of rootfs (including itself),
+//config: does a mount --move that overmounts rootfs with the new root, and
+//config: then execs the specified init program.
+//config:
+//config: util-linux has a similar tool, switch-root.
+//config: run-init differs by also having a "-d CAPS_TO_DROP" option.
+
+/* applet and kbuild hooks are in switch_root.c */
diff --git a/libbb/capability.c b/libbb/capability.c
index 692024f..f60062b 100644
--- a/libbb/capability.c
+++ b/libbb/capability.c
@@ -6,6 +6,14 @@
//kbuild:lib-$(CONFIG_PLATFORM_LINUX) += capability.o
#include <linux/capability.h>
+// #include <sys/capability.h>
+// This header is in libcap, but the functions are in libc.
+// Comment in the header says this above capset/capget:
+/* system calls - look to libc for function to system call mapping */
+extern int capset(cap_user_header_t header, cap_user_data_t data);
+extern int capget(cap_user_header_t header, const cap_user_data_t data);
+// so for bbox, let's just repeat the declarations.
+// This way, libcap needs not be installed in build environment.
#include "libbb.h"
static const char *const capabilities[] = {
@@ -77,3 +85,42 @@ void FAST_FUNC printf_cap(const char *pfx, unsigned cap_no)
}
printf("%scap_%u", pfx, cap_no);
}
+
+DEFINE_STRUCT_CAPS;
+
+void FAST_FUNC getcaps(void *arg)
+{
+ static const uint8_t versions[] = {
+ _LINUX_CAPABILITY_U32S_3, /* = 2 (fits into byte) */
+ _LINUX_CAPABILITY_U32S_2, /* = 2 */
+ _LINUX_CAPABILITY_U32S_1, /* = 1 */
+ };
+ int i;
+ struct caps *caps = arg;
+
+ 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");
+ }
+
+ if (capget(&caps->header, caps->data) != 0)
+ bb_simple_perror_msg_and_die("capget");
+}
diff --git a/util-linux/setpriv.c b/util-linux/setpriv.c
index 9f27939..12ab1bd 100644
--- a/util-linux/setpriv.c
+++ b/util-linux/setpriv.c
@@ -124,48 +124,7 @@ enum {
};
#if ENABLE_FEATURE_SETPRIV_CAPABILITIES
-struct caps {
- struct __user_cap_header_struct header;
- cap_user_data_t data;
- int u32s;
-};
-
-static void getcaps(struct caps *caps)
-{
- static const uint8_t versions[] = {
- _LINUX_CAPABILITY_U32S_3, /* = 2 (fits into byte) */
- _LINUX_CAPABILITY_U32S_2, /* = 2 */
- _LINUX_CAPABILITY_U32S_1, /* = 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");
-}
+DEFINE_STRUCT_CAPS;
static unsigned parse_cap(const char *cap)
{
@@ -195,7 +154,7 @@ static void set_inh_caps(char *capstring)
cap = parse_cap(capstring);
if (CAP_TO_INDEX(cap) >= caps.u32s)
- bb_error_msg_and_die("invalid capability cap");
+ bb_error_msg_and_die("invalid capability '%s'", capstring);
if (capstring[0] == '+')
caps.data[CAP_TO_INDEX(cap)].inheritable |= CAP_TO_MASK(cap);
@@ -204,11 +163,8 @@ static void set_inh_caps(char *capstring)
capstring = strtok(NULL, ",");
}
- if ((capset(&caps.header, caps.data)) < 0)
+ if (capset(&caps.header, caps.data) != 0)
bb_perror_msg_and_die("capset");
-
- if (ENABLE_FEATURE_CLEAN_UP)
- free(caps.data);
}
static void set_ambient_caps(char *string)
@@ -322,10 +278,9 @@ static int dump(void)
bb_putchar('\n');
# endif
- if (ENABLE_FEATURE_CLEAN_UP) {
- IF_FEATURE_SETPRIV_CAPABILITIES(free(caps.data);)
+ if (ENABLE_FEATURE_CLEAN_UP)
free(gids);
- }
+
return EXIT_SUCCESS;
}
#endif /* FEATURE_SETPRIV_DUMP */
diff --git a/util-linux/switch_root.c b/util-linux/switch_root.c
index fb6057a..fe9ab68 100644
--- a/util-linux/switch_root.c
+++ b/util-linux/switch_root.c
@@ -26,20 +26,46 @@
//config: list of active mount points. That's why.
//applet:IF_SWITCH_ROOT(APPLET(switch_root, BB_DIR_SBIN, BB_SUID_DROP))
+// APPLET_ODDNAME:name main location suid_type help
+//applet:IF_RUN_INIT( APPLET_ODDNAME(run-init, switch_root, BB_DIR_SBIN, BB_SUID_DROP, run_init))
//kbuild:lib-$(CONFIG_SWITCH_ROOT) += switch_root.o
+//kbuild:lib-$(CONFIG_RUN_INIT) += switch_root.o
//usage:#define switch_root_trivial_usage
-//usage: "[-c /dev/console] NEW_ROOT NEW_INIT [ARGS]"
+//usage: "[-c CONSOLE_DEV] NEW_ROOT NEW_INIT [ARGS]"
//usage:#define switch_root_full_usage "\n\n"
//usage: "Free initramfs and switch to another root fs:\n"
//usage: "chroot to NEW_ROOT, delete all in /, move NEW_ROOT to /,\n"
//usage: "execute NEW_INIT. PID must be 1. NEW_ROOT must be a mountpoint.\n"
//usage: "\n -c DEV Reopen stdio to DEV after switch"
+//usage:#define run_init_trivial_usage
+//usage: "[-d CAP,CAP...] [-c CONSOLE_DEV] NEW_ROOT NEW_INIT [ARGS]"
+//usage:#define run_init_full_usage "\n\n"
+//usage: "Free initramfs and switch to another root fs:\n"
+//usage: "chroot to NEW_ROOT, delete all in /, move NEW_ROOT to /,\n"
+//usage: "execute NEW_INIT. PID must be 1. NEW_ROOT must be a mountpoint.\n"
+//usage: "\n -c DEV Reopen stdio to DEV after switch"
+//usage: "\n -d CAPS Drop capabilities"
+
#include <sys/vfs.h>
#include <sys/mount.h>
+#if ENABLE_RUN_INIT
+# include <sys/prctl.h>
+# include <linux/capability.h>
+// #include <sys/capability.h>
+// This header is in libcap, but the functions are in libc.
+// Comment in the header says this above capset/capget:
+/* system calls - look to libc for function to system call mapping */
+extern int capset(cap_user_header_t header, cap_user_data_t data);
+extern int capget(cap_user_header_t header, const cap_user_data_t data);
+// so for bbox, let's just repeat the declarations.
+// This way, libcap needs not be installed in build environment.
+#endif
+
#include "libbb.h"
+
// Make up for header deficiencies
#ifndef RAMFS_MAGIC
# define RAMFS_MAGIC ((unsigned)0x858458f6)
@@ -89,6 +115,84 @@ static void delete_contents(const char *directory, dev_t rootdev)
}
}
+#if ENABLE_RUN_INIT
+DEFINE_STRUCT_CAPS;
+
+static void drop_capset(int cap_idx)
+{
+ struct caps caps;
+
+ /* Get the current capability mask */
+ getcaps(&caps);
+
+ /* Drop the bit */
+ caps.data[CAP_TO_INDEX(cap_idx)].inheritable &= ~CAP_TO_MASK(cap_idx);
+
+ /* And drop the capability. */
+ if (capset(&caps.header, caps.data) != 0)
+ bb_perror_msg_and_die("capset");
+}
+
+static void drop_bounding_set(int cap_idx)
+{
+ int ret;
+
+ ret = prctl(PR_CAPBSET_READ, cap_idx, 0, 0, 0);
+ if (ret < 0)
+ bb_perror_msg_and_die("prctl: %s", "PR_CAPBSET_READ");
+
+ if (ret == 1) {
+ ret = prctl(PR_CAPBSET_DROP, cap_idx, 0, 0, 0);
+ if (ret != 0)
+ bb_perror_msg_and_die("prctl: %s", "PR_CAPBSET_DROP");
+ }
+}
+
+static void drop_usermodehelper(const char *filename, int cap_idx)
+{
+ unsigned lo, hi;
+ char buf[sizeof(int)*3 * 2 + 8];
+ int fd;
+ int ret;
+
+ ret = open_read_close(filename, buf, sizeof(buf) - 1);
+ if (ret < 0)
+ return; /* assuming files do not exist */
+
+ buf[ret] = '\0';
+ ret = sscanf(buf, "%u %u", &lo, &hi);
+ if (ret != 2)
+ bb_perror_msg_and_die("can't parse file '%s'", filename);
+
+ if (cap_idx < 32)
+ lo &= ~(1 << cap_idx);
+ else
+ hi &= ~(1 << (cap_idx - 32));
+
+ fd = xopen(filename, O_WRONLY);
+ fdprintf(fd, "%u %u", lo, hi);
+ close(fd);
+}
+
+static void drop_capabilities(char *string)
+{
+ char *cap;
+
+ cap = strtok(string, ",");
+ while (cap) {
+ unsigned cap_idx;
+
+ cap_idx = cap_name_to_number(cap);
+ drop_usermodehelper("/proc/sys/kernel/usermodehelper/bset", cap_idx);
+ drop_usermodehelper("/proc/sys/kernel/usermodehelper/inheritable", cap_idx);
+ drop_bounding_set(cap_idx);
+ drop_capset(cap_idx);
+ bb_error_msg("dropped capability: %s", cap);
+ cap = strtok(NULL, ",");
+ }
+}
+#endif
+
int switch_root_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
int switch_root_main(int argc UNUSED_PARAM, char **argv)
{
@@ -98,7 +202,25 @@ int switch_root_main(int argc UNUSED_PARAM, char **argv)
dev_t rootdev;
// Parse args (-c console). '+': stop at first non-option
- getopt32(argv, "^+" "c:" "\0" "-2" /* minimum 2 args */, &console);
+ if (ENABLE_SWITCH_ROOT && (!ENABLE_RUN_INIT || applet_name[0] == 's')) {
+ getopt32(argv, "^+"
+ "c:"
+ "\0" "-2" /* minimum 2 args */,
+ &console
+ );
+ } else {
+#if ENABLE_RUN_INIT
+ char *cap_list = NULL;
+ getopt32(argv, "^+"
+ "c:d:"
+ "\0" "-2" /* minimum 2 args */,
+ &console,
+ &cap_list
+ );
+ if (cap_list)
+ drop_capabilities(cap_list);
+#endif
+ }
argv += optind;
newroot = *argv++;
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