[klibc] [klibc:master] run-init: Add dry-run mode
klibc-bot for Ben Hutchings
ben at decadent.org.uk
Fri Jan 18 08:42:05 PST 2019
Commit-ID: 10059fddba9f8bec6aeb0d37d217df6d65e64c3b
Gitweb: http://git.kernel.org/?p=libs/klibc/klibc.git;a=commit;h=10059fddba9f8bec6aeb0d37d217df6d65e64c3b
Author: Ben Hutchings <ben at decadent.org.uk>
AuthorDate: Sun, 17 Jan 2016 19:50:28 +0000
Committer: Ben Hutchings <ben at decadent.org.uk>
CommitDate: Wed, 2 Jan 2019 03:08:04 +0000
[klibc] run-init: Add dry-run mode
initramfs-tools wants to validate the real init program before running
it, as there is no way out once it has exec'd run-init. This is
complicated by the increasing use of symlinks for /sbin/init and for
/sbin itself. We can't simply resolve them with 'readlink -f' because
any absolute symlinks will be resolved using the wrong root. Add a
dry-run mode (-n option) to run-init that goes as far as possible to
validate that the given init is executable.
References: https://bugs.debian.org/810965
Link: https://www.zytor.com/pipermail/klibc/2017-December/003973.html
Signed-off-by: Ben Hutchings <ben at decadent.org.uk>
---
usr/kinit/kinit.c | 2 +-
usr/kinit/run-init/run-init.c | 37 +++++++++++++++++++++++-------------
usr/kinit/run-init/run-init.h | 5 ++++-
usr/kinit/run-init/runinitlib.c | 42 +++++++++++++++++++++++++++--------------
4 files changed, 57 insertions(+), 29 deletions(-)
diff --git a/usr/kinit/kinit.c b/usr/kinit/kinit.c
index 523c92b..de03c2d 100644
--- a/usr/kinit/kinit.c
+++ b/usr/kinit/kinit.c
@@ -304,7 +304,7 @@ int main(int argc, char *argv[])
init_argv[0] = strrchr(init_path, '/') + 1;
errmsg = run_init("/root", "/dev/console",
- get_arg(cmdc, cmdv, "drop_capabilities="),
+ get_arg(cmdc, cmdv, "drop_capabilities="), false,
init_path, init_argv);
/* If run_init returned, something went bad */
diff --git a/usr/kinit/run-init/run-init.c b/usr/kinit/run-init/run-init.c
index 2147d06..a14ce7c 100644
--- a/usr/kinit/run-init/run-init.c
+++ b/usr/kinit/run-init/run-init.c
@@ -26,19 +26,23 @@
* ----------------------------------------------------------------------- */
/*
- * Usage: exec run-init [-d caps] [-c /dev/console] /real-root /sbin/init "$@"
+ * Usage: exec run-init [-d caps] [-c /dev/console] [-n] /real-root /sbin/init "$@"
*
* This program should be called as the last thing in a shell script
* acting as /init in an initramfs; it does the following:
*
- * - Delete all files in the initramfs;
- * - Remounts /real-root onto the root filesystem;
- * - Drops comma-separated list of capabilities;
- * - Chroots;
- * - Opens /dev/console;
- * - Spawns the specified init program (with arguments.)
+ * 1. Delete all files in the initramfs;
+ * 2. Remounts /real-root onto the root filesystem;
+ * 3. Drops comma-separated list of capabilities;
+ * 4. Chroots;
+ * 5. Opens /dev/console;
+ * 6. Spawns the specified init program (with arguments.)
+ *
+ * With the -n option, it skips steps 1, 2 and 6 and can be used to check
+ * whether the given root and init are likely to work.
*/
+#include <stdbool.h>
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
@@ -51,7 +55,7 @@ static const char *program;
static void __attribute__ ((noreturn)) usage(void)
{
fprintf(stderr,
- "Usage: exec %s [-d caps] [-c consoledev] /real-root /sbin/init [args]\n",
+ "Usage: exec %s [-d caps] [-c consoledev] [-n] /real-root /sbin/init [args]\n",
program);
exit(1);
}
@@ -64,6 +68,7 @@ int main(int argc, char *argv[])
const char *init;
const char *error;
const char *drop_caps = NULL;
+ bool dry_run = false;
char **initargs;
/* Variables... */
@@ -72,11 +77,13 @@ int main(int argc, char *argv[])
/* Parse the command line */
program = argv[0];
- while ((o = getopt(argc, argv, "c:d:")) != -1) {
+ while ((o = getopt(argc, argv, "c:d:n")) != -1) {
if (o == 'c') {
console = optarg;
} else if (o == 'd') {
drop_caps = optarg;
+ } else if (o == 'n') {
+ dry_run = true;
} else {
usage();
}
@@ -89,9 +96,13 @@ int main(int argc, char *argv[])
init = argv[optind + 1];
initargs = argv + optind + 1;
- error = run_init(realroot, console, drop_caps, init, initargs);
+ error = run_init(realroot, console, drop_caps, dry_run, init, initargs);
- /* If run_init returns, something went wrong */
- fprintf(stderr, "%s: %s: %s\n", program, error, strerror(errno));
- return 1;
+ if (error) {
+ fprintf(stderr, "%s: %s: %s\n", program, error, strerror(errno));
+ return 1;
+ } else {
+ /* Must have been a dry run */
+ return 0;
+ }
}
diff --git a/usr/kinit/run-init/run-init.h b/usr/kinit/run-init/run-init.h
index da3136a..02c34aa 100644
--- a/usr/kinit/run-init/run-init.h
+++ b/usr/kinit/run-init/run-init.h
@@ -28,7 +28,10 @@
#ifndef RUN_INIT_H
#define RUN_INIT_H
+#include <stdbool.h>
+
const char *run_init(const char *realroot, const char *console,
- const char *drop_caps, const char *init, char **initargs);
+ const char *drop_caps, bool dry_run,
+ const char *init, char **initargs);
#endif
diff --git a/usr/kinit/run-init/runinitlib.c b/usr/kinit/run-init/runinitlib.c
index fe856bd..74d7883 100644
--- a/usr/kinit/run-init/runinitlib.c
+++ b/usr/kinit/run-init/runinitlib.c
@@ -156,10 +156,10 @@ static int nuke(const char *what)
}
const char *run_init(const char *realroot, const char *console,
- const char *drop_caps, const char *init,
+ const char *drop_caps, bool dry_run, const char *init,
char **initargs)
{
- struct stat rst, cst;
+ struct stat rst, cst, ist;
struct statfs sfs;
int confd;
@@ -186,13 +186,15 @@ const char *run_init(const char *realroot, const char *console,
/* Okay, I think we should be safe... */
- /* Delete rootfs contents */
- if (nuke_dir("/"))
- return "nuking initramfs contents";
+ if (!dry_run) {
+ /* Delete rootfs contents */
+ if (nuke_dir("/"))
+ return "nuking initramfs contents";
- /* Overmount the root */
- if (mount(".", "/", NULL, MS_MOVE, NULL))
- return "overmounting root";
+ /* Overmount the root */
+ if (mount(".", "/", NULL, MS_MOVE, NULL))
+ return "overmounting root";
+ }
/* chroot, chdir */
if (chroot(".") || chdir("/"))
@@ -205,12 +207,24 @@ const char *run_init(const char *realroot, const char *console,
/* Open /dev/console */
if ((confd = open(console, O_RDWR)) < 0)
return "opening console";
- dup2(confd, 0);
- dup2(confd, 1);
- dup2(confd, 2);
+ if (!dry_run) {
+ dup2(confd, 0);
+ dup2(confd, 1);
+ dup2(confd, 2);
+ }
close(confd);
- /* Spawn init */
- execv(init, initargs);
- return init; /* Failed to spawn init */
+ if (!dry_run) {
+ /* Spawn init */
+ execv(init, initargs);
+ return init; /* Failed to spawn init */
+ } else {
+ if (stat(init, &ist))
+ return init;
+ if (!S_ISREG(ist.st_mode) || !(ist.st_mode & S_IXUGO)) {
+ errno = EACCES;
+ return init;
+ }
+ return NULL; /* Success */
+ }
}
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