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systemd/src/shared/killall.c
T
Mike Yuan 374c29fc88 shared/killall: correctly warn about rootfs daemon's root 
Follow-up for 9e615117da

We'll typically send signals to all remaining processes in the following
cases:

1. pid1 (in initrd) when transitioning from initrd to sysroot: SIGTERM
2. pid1 (in sysroot) before transitioning back to initrd (exitrd): SIGTERM + SIGKILL
3. systemd-shutdown (in exitrd): SIGTERM + SIGKILL

'warn_rootfs' is set to true only when we're not in initrd and we're
sending SIGKILL, which means the second case. So, we want to emit the
warning when the root of the storage daemon IS the same as that of pid1,
rather than the other way around.

The condition is spuriously reversed in the offending commit.
2023-12-06 22:03:35 +01:00

320 lines
11 KiB
C
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/* SPDX-License-Identifier: LGPL-2.1-or-later */
/***
Copyright © 2010 ProFUSION embedded systems
***/
#include <errno.h>
#include <signal.h>
#include <sys/wait.h>
#include <unistd.h>
#include "alloc-util.h"
#include "constants.h"
#include "dirent-util.h"
#include "errno-util.h"
#include "fd-util.h"
#include "format-util.h"
#include "initrd-util.h"
#include "killall.h"
#include "parse-util.h"
#include "process-util.h"
#include "set.h"
#include "stdio-util.h"
#include "string-util.h"
#include "terminal-util.h"
static bool argv_has_at(pid_t pid) {
_cleanup_fclose_ FILE *f = NULL;
const char *p;
char c = 0;
p = procfs_file_alloca(pid, "cmdline");
f = fopen(p, "re");
if (!f) {
log_debug_errno(errno, "Failed to open %s, ignoring: %m", p);
return true; /* not really, but has the desired effect */
}
/* Try to read the first character of the command line. If the cmdline is empty (which might be the case for
* kernel threads but potentially also other stuff), this line won't do anything, but we don't care much, as
* actual kernel threads are already filtered out above. */
(void) fread(&c, 1, 1, f);
/* Processes with argv[0][0] = '@' we ignore from the killing spree.
*
* https://systemd.io/ROOT_STORAGE_DAEMONS */
return c == '@';
}
static bool is_survivor_cgroup(const PidRef *pid) {
_cleanup_free_ char *cgroup_path = NULL;
int r;
assert(pidref_is_set(pid));
r = cg_pidref_get_path(/* root= */ NULL, pid, &cgroup_path);
if (r < 0) {
log_warning_errno(r, "Failed to get cgroup path of process " PID_FMT ", ignoring: %m", pid->pid);
return false;
}
r = cg_get_xattr_bool(cgroup_path, "user.survive_final_kill_signal");
/* user xattr support was added to kernel v5.7, try with the trusted namespace as a fallback */
if (ERRNO_IS_NEG_XATTR_ABSENT(r))
r = cg_get_xattr_bool(cgroup_path, "trusted.survive_final_kill_signal");
if (r < 0 && !ERRNO_IS_NEG_XATTR_ABSENT(r))
log_debug_errno(r,
"Failed to get survive_final_kill_signal xattr of %s, ignoring: %m",
cgroup_path);
return r > 0;
}
static bool ignore_proc(const PidRef *pid, bool warn_rootfs) {
uid_t uid;
int r;
assert(pidref_is_set(pid));
/* We are PID 1, let's not commit suicide */
if (pid->pid == 1)
return true;
/* Ignore kernel threads */
r = pidref_is_kernel_thread(pid);
if (r != 0)
return true; /* also ignore processes where we can't determine this */
/* Ignore processes that are part of a cgroup marked with the user.survive_final_kill_signal xattr */
if (is_survivor_cgroup(pid))
return true;
r = pidref_get_uid(pid, &uid);
if (r < 0)
return true; /* not really, but better safe than sorry */
/* Non-root processes otherwise are always subject to be killed */
if (uid != 0)
return false;
if (!argv_has_at(pid->pid))
return false;
if (warn_rootfs &&
pid_from_same_root_fs(pid->pid) > 0) {
_cleanup_free_ char *comm = NULL;
(void) pidref_get_comm(pid, &comm);
log_notice("Process " PID_FMT " (%s) has been marked to be excluded from killing. It is "
"running from the root file system, and thus likely to block re-mounting of the "
"root file system to read-only. Please consider moving it into an initrd file "
"system instead.", pid->pid, strna(comm));
}
return true;
}
static void log_children_no_yet_killed(Set *pids) {
_cleanup_free_ char *lst_child = NULL;
void *p;
int r;
SET_FOREACH(p, pids) {
_cleanup_free_ char *s = NULL;
if (pid_get_comm(PTR_TO_PID(p), &s) >= 0)
r = strextendf(&lst_child, ", " PID_FMT " (%s)", PTR_TO_PID(p), s);
else
r = strextendf(&lst_child, ", " PID_FMT, PTR_TO_PID(p));
if (r < 0)
return (void) log_oom_warning();
}
if (isempty(lst_child))
return;
log_warning("Waiting for process: %s", lst_child + 2);
}
static int wait_for_children(Set *pids, sigset_t *mask, usec_t timeout) {
usec_t until, date_log_child, n;
assert(mask);
/* Return the number of children remaining in the pids set: That correspond to the number
* of processes still "alive" after the timeout */
if (set_isempty(pids))
return 0;
n = now(CLOCK_MONOTONIC);
until = usec_add(n, timeout);
date_log_child = usec_add(n, 10u * USEC_PER_SEC);
if (date_log_child > until)
date_log_child = usec_add(n, timeout / 2u);
for (;;) {
struct timespec ts;
int k;
void *p;
/* First, let the kernel inform us about killed
* children. Most processes will probably be our
* children, but some are not (might be our
* grandchildren instead...). */
for (;;) {
pid_t pid;
pid = waitpid(-1, NULL, WNOHANG);
if (pid == 0)
break;
if (pid < 0) {
if (errno == ECHILD)
break;
return log_error_errno(errno, "waitpid() failed: %m");
}
(void) set_remove(pids, PID_TO_PTR(pid));
}
/* Now explicitly check who might be remaining, who
* might not be our child. */
SET_FOREACH(p, pids) {
/* kill(pid, 0) sends no signal, but it tells
* us whether the process still exists. */
if (kill(PTR_TO_PID(p), 0) == 0)
continue;
if (errno != ESRCH)
continue;
set_remove(pids, p);
}
if (set_isempty(pids))
return 0;
n = now(CLOCK_MONOTONIC);
if (date_log_child > 0 && n >= date_log_child) {
log_children_no_yet_killed(pids);
/* Log the children not yet killed only once */
date_log_child = 0;
}
if (n >= until)
return set_size(pids);
if (date_log_child > 0)
timespec_store(&ts, MIN(until - n, date_log_child - n));
else
timespec_store(&ts, until - n);
k = sigtimedwait(mask, NULL, &ts);
if (k != SIGCHLD) {
if (k < 0 && errno != EAGAIN)
return log_error_errno(errno, "sigtimedwait() failed: %m");
if (k >= 0)
log_warning("sigtimedwait() returned unexpected signal.");
}
}
}
static int killall(int sig, Set *pids, bool send_sighup) {
_cleanup_closedir_ DIR *dir = NULL;
int n_killed = 0, r;
/* Send the specified signal to all remaining processes, if not excluded by ignore_proc().
* Returns the number of processes to which the specified signal was sent */
r = proc_dir_open(&dir);
if (r < 0)
return log_warning_errno(r, "opendir(/proc) failed: %m");
for (;;) {
_cleanup_(pidref_done) PidRef pidref = PIDREF_NULL;
r = proc_dir_read_pidref(dir, &pidref);
if (r < 0)
return log_warning_errno(r, "Failed to enumerate /proc: %m");
if (r == 0)
break;
if (ignore_proc(&pidref, sig == SIGKILL && !in_initrd()))
continue;
if (sig == SIGKILL) {
_cleanup_free_ char *s = NULL;
(void) pidref_get_comm(&pidref, &s);
log_notice("Sending SIGKILL to PID "PID_FMT" (%s).", pidref.pid, strna(s));
}
r = pidref_kill(&pidref, sig);
if (r < 0) {
if (errno != -ESRCH)
log_warning_errno(errno, "Could not kill " PID_FMT ", ignoring: %m", pidref.pid);
} else {
n_killed++;
if (pids) {
r = set_put(pids, PID_TO_PTR(pidref.pid));
if (r < 0)
(void) log_oom_warning();
}
}
if (send_sighup) {
/* Optionally, also send a SIGHUP signal, but only if the process has a controlling
* tty. This is useful to allow handling of shells which ignore SIGTERM but react to
* SIGHUP. We do not send this to processes that have no controlling TTY since we
* don't want to trigger reloads of daemon processes. Also we make sure to only send
* this after SIGTERM so that SIGTERM is always first in the queue. */
if (get_ctty_devnr(pidref.pid, NULL) >= 0)
/* it's OK if the process is gone, just ignore the result */
(void) pidref_kill(&pidref, SIGHUP);
}
}
return n_killed;
}
int broadcast_signal(int sig, bool wait_for_exit, bool send_sighup, usec_t timeout) {
int n_children_left;
sigset_t mask, oldmask;
_cleanup_set_free_ Set *pids = NULL;
/* Send the specified signal to all remaining processes, if not excluded by ignore_proc().
* Return:
* - The number of processes still "alive" after the timeout (that should have been killed)
* if the function needs to wait for the end of the processes (wait_for_exit).
* - Otherwise, the number of processes to which the specified signal was sent */
if (wait_for_exit)
pids = set_new(NULL);
assert_se(sigemptyset(&mask) == 0);
assert_se(sigaddset(&mask, SIGCHLD) == 0);
assert_se(sigprocmask(SIG_BLOCK, &mask, &oldmask) == 0);
if (kill(-1, SIGSTOP) < 0 && errno != ESRCH)
log_warning_errno(errno, "kill(-1, SIGSTOP) failed: %m");
n_children_left = killall(sig, pids, send_sighup);
if (kill(-1, SIGCONT) < 0 && errno != ESRCH)
log_warning_errno(errno, "kill(-1, SIGCONT) failed: %m");
if (wait_for_exit && n_children_left > 0)
n_children_left = wait_for_children(pids, &mask, timeout);
assert_se(sigprocmask(SIG_SETMASK, &oldmask, NULL) == 0);
return n_children_left;
}
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