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run-init: new applet

Browse source 
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@googlemail.com>
This commit is contained in:
Denys Vlasenko 2017-08-21 19:30:01 +02:00
parent 44b3f2ffbc
commit 200bcc851a
5 changed files with 212 additions and 52 deletions
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126
util-linux/switch_root.c
View file

@ -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++;