signalfuncs.c

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/*-------------------------------------------------------------------------
 *
 * signalfuncs.c
 *    Functions for signaling backends
 *
 * Portions Copyright (c) 1996-2020, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/backend/storage/ipc/signalfuncs.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include <signal.h>

#include "catalog/pg_authid.h"
#include "miscadmin.h"
#include "postmaster/syslogger.h"
#include "storage/pmsignal.h"
#include "storage/proc.h"
#include "storage/procarray.h"
#include "utils/acl.h"
#include "utils/builtins.h"


/*
 * Send a signal to another backend.
 *
 * The signal is delivered if the user is either a superuser or the same
 * role as the backend being signaled. For "dangerous" signals, an explicit
 * check for superuser needs to be done prior to calling this function.
 *
 * Returns 0 on success, 1 on general failure, 2 on normal permission error
 * and 3 if the caller needs to be a superuser.
 *
 * In the event of a general failure (return code 1), a warning message will
 * be emitted. For permission errors, doing that is the responsibility of
 * the caller.
 */
#define SIGNAL_BACKEND_SUCCESS 0
#define SIGNAL_BACKEND_ERROR 1
#define SIGNAL_BACKEND_NOPERMISSION 2
#define SIGNAL_BACKEND_NOSUPERUSER 3
static int
pg_signal_backend(int pid, int sig)
{
    PGPROC     *proc = BackendPidGetProc(pid);

    /*
     * BackendPidGetProc returns NULL if the pid isn't valid; but by the time
     * we reach kill(), a process for which we get a valid proc here might
     * have terminated on its own.  There's no way to acquire a lock on an
     * arbitrary process to prevent that. But since so far all the callers of
     * this mechanism involve some request for ending the process anyway, that
     * it might end on its own first is not a problem.
     */
    if (proc == NULL)
    {
        /*
         * This is just a warning so a loop-through-resultset will not abort
         * if one backend terminated on its own during the run.
         */
        ereport(WARNING,
                (errmsg("PID %d is not a PostgreSQL server process", pid)));
        return SIGNAL_BACKEND_ERROR;
    }

    /* Only allow superusers to signal superuser-owned backends. */
    if (superuser_arg(proc->roleId) && !superuser())
        return SIGNAL_BACKEND_NOSUPERUSER;

    /* Users can signal backends they have role membership in. */
    if (!has_privs_of_role(GetUserId(), proc->roleId) &&
        !has_privs_of_role(GetUserId(), DEFAULT_ROLE_SIGNAL_BACKENDID))
        return SIGNAL_BACKEND_NOPERMISSION;

    /*
     * Can the process we just validated above end, followed by the pid being
     * recycled for a new process, before reaching here?  Then we'd be trying
     * to kill the wrong thing.  Seems near impossible when sequential pid
     * assignment and wraparound is used.  Perhaps it could happen on a system
     * where pid re-use is randomized.  That race condition possibility seems
     * too unlikely to worry about.
     */

    /* If we have setsid(), signal the backend's whole process group */
#ifdef HAVE_SETSID
    if (kill(-pid, sig))
#else
    if (kill(pid, sig))
#endif
    {
        /* Again, just a warning to allow loops */
        ereport(WARNING,
                (errmsg("could not send signal to process %d: %m", pid)));
        return SIGNAL_BACKEND_ERROR;
    }
    return SIGNAL_BACKEND_SUCCESS;
}

/*
 * Signal to cancel a backend process.  This is allowed if you are a member of
 * the role whose process is being canceled.
 *
 * Note that only superusers can signal superuser-owned processes.
 */
Datum
pg_cancel_backend(PG_FUNCTION_ARGS)
{
    int         r = pg_signal_backend(PG_GETARG_INT32(0), SIGINT);

    if (r == SIGNAL_BACKEND_NOSUPERUSER)
        ereport(ERROR,
                (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
                 errmsg("must be a superuser to cancel superuser query")));

    if (r == SIGNAL_BACKEND_NOPERMISSION)
        ereport(ERROR,
                (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
                 errmsg("must be a member of the role whose query is being canceled or member of pg_signal_backend")));

    PG_RETURN_BOOL(r == SIGNAL_BACKEND_SUCCESS);
}

/*
 * Signal to terminate a backend process.  This is allowed if you are a member
 * of the role whose process is being terminated.
 *
 * Note that only superusers can signal superuser-owned processes.
 */
Datum
pg_terminate_backend(PG_FUNCTION_ARGS)
{
    int         r = pg_signal_backend(PG_GETARG_INT32(0), SIGTERM);

    if (r == SIGNAL_BACKEND_NOSUPERUSER)
        ereport(ERROR,
                (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
                 errmsg("must be a superuser to terminate superuser process")));

    if (r == SIGNAL_BACKEND_NOPERMISSION)
        ereport(ERROR,
                (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
                 errmsg("must be a member of the role whose process is being terminated or member of pg_signal_backend")));

    PG_RETURN_BOOL(r == SIGNAL_BACKEND_SUCCESS);
}

/*
 * Signal to reload the database configuration
 *
 * Permission checking for this function is managed through the normal
 * GRANT system.
 */
Datum
pg_reload_conf(PG_FUNCTION_ARGS)
{
    if (kill(PostmasterPid, SIGHUP))
    {
        ereport(WARNING,
                (errmsg("failed to send signal to postmaster: %m")));
        PG_RETURN_BOOL(false);
    }

    PG_RETURN_BOOL(true);
}


/*
 * Rotate log file
 *
 * This function is kept to support adminpack 1.0.
 */
Datum
pg_rotate_logfile(PG_FUNCTION_ARGS)
{
    if (!superuser())
        ereport(ERROR,
                (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
                 errmsg("must be superuser to rotate log files with adminpack 1.0"),
        /* translator: %s is a SQL function name */
                 errhint("Consider using %s, which is part of core, instead.",
                         "pg_logfile_rotate()")));

    if (!Logging_collector)
    {
        ereport(WARNING,
                (errmsg("rotation not possible because log collection not active")));
        PG_RETURN_BOOL(false);
    }

    SendPostmasterSignal(PMSIGNAL_ROTATE_LOGFILE);
    PG_RETURN_BOOL(true);
}

/*
 * Rotate log file
 *
 * Permission checking for this function is managed through the normal
 * GRANT system.
 */
Datum
pg_rotate_logfile_v2(PG_FUNCTION_ARGS)
{
    if (!Logging_collector)
    {
        ereport(WARNING,
                (errmsg("rotation not possible because log collection not active")));
        PG_RETURN_BOOL(false);
    }

    SendPostmasterSignal(PMSIGNAL_ROTATE_LOGFILE);
    PG_RETURN_BOOL(true);
}