/*
    This file is part of the KDE libraries
    SPDX-FileCopyrightText: 2006 Lubos Lunak <l.lunak@kde.org>

    SPDX-License-Identifier: LGPL-2.0-only
*/

#include <config-kdeinit.h>

#define _POSIX_C_SOURCE 200809L /* kill(2) */

#include <errno.h>
#include <fcntl.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/stat.h>
#include <unistd.h>
#if HAVE_CAPABILITIES
#include <sys/capability.h>
#endif

#define EXECUTE KDE_INSTALL_FULL_BINDIR "/kdeinit5"

#if KDEINIT_OOM_PROTECT

/*
 Prevent getting killed by bad heuristic in Linux OOM-killer.
 This wrapper decreases the chance OOM killer kills it (or its children,
 namely kdeinit), opens a pipe and forks. Child drops privileges
 and launches kdeinit. Since processes started by kdeinit should
 not have this protection, kdeinit will after forking send the new
 PID using the pipe and wait for a signal. This parent will reset the protection
 and SIGUSR1 the process to continue.
 returns 1 if pid is valid
*/

static int set_protection(pid_t pid, int enable)
{
    char buf[ 1024 ];
    int procfile;
    struct stat st;
    /* Newer kernels (noticed in 2.6.36) */
    sprintf(buf, "/proc/%d/oom_score_adj", pid);
    if (lstat(buf, &st) == 0) {
        if (!enable) {
            /* Be paranoid and check that the pid we got from the pipe
               belongs to this user. */
            if (st.st_uid != getuid()) {
                return 0;
            }
        }
        procfile = open(buf, O_WRONLY);
        if (enable) {
            write(procfile, "-300", sizeof("-300"));
        } else {
            write(procfile, "0", sizeof("0"));
        }
        close(procfile);
        return 1;
    }

    sprintf(buf, "/proc/%d/stat", pid);
    if (!enable) {
        /* Be paranoid and check that the pid we got from the pipe
           belongs to this user. */
        if (lstat(buf, &st) < 0 || st.st_uid != getuid()) {
            return 0;
        }
    }
    sprintf(buf, "/proc/%d/oom_adj", pid);
    procfile = open(buf, O_WRONLY);
    if (procfile >= 0) {
        if (enable) {
            write(procfile, "-5", sizeof("-5"));
        } else {
            write(procfile, "0", sizeof("0"));
        }
        close(procfile);
    }
    return 1;
}

int main(int argc, char **argv)
{
    int pipes[ 2 ];
    int new_argc;
    const char **new_argv;
    char helper_num[ 1024 ];
    unsigned i;
    char **orig_environ = NULL;
    char header[ 7 ];
#if HAVE_CAPABILITIES
    cap_t caps;
#endif
    if (pipe(pipes) < 0) {
        perror("pipe()");
        return 1;
    }
    if (argc < 0 || argc > 1000) {
        abort();    /* paranoid */
    }
    set_protection(getpid(), 1);
    switch (fork()) {
    case -1:
        perror("fork()");
        return 1;
    default: /* parent, drop privileges and exec */
#if HAVE_CAPABILITIES
        caps = cap_init();
        if (cap_set_proc(caps) < 0) {
            perror("cap_set_proc()");
            return 1;
        }
        cap_free(caps);
#endif
        if (setgid(getgid())) {
            perror("setgid()");
            return 1;
        }
        if (setuid(getuid()) || geteuid() != getuid()) {
            perror("setuid()");
            return 1;
        }
        close(pipes[ 0 ]);
        /* read original environment passed by start_kdeinit_wrapper */
        if (read(0, header, 7) == 7 && strncmp(header, "environ", 7) == 0) {
            unsigned count;
            if (read(0, &count, sizeof(unsigned)) == sizeof(unsigned)
                    && count && count < (1 << 16)) {
                char **env = malloc((count + 1) * sizeof(char *));
                int ok = 1;
                for (i = 0;
                        i < count && ok;
                        ++i) {
                    unsigned len;
                    if (read(0, &len, sizeof(unsigned)) == sizeof(unsigned)
                            && len && len < (1 << 12)) {
                        env[ i ] = malloc(len + 1);
                        if ((unsigned) read(0, env[ i ], len) == len) {
                            env[ i ][ len ] = '\0';
                        } else {
                            ok = 0;
                        }
                    }
                }
                if (ok) {
                    env[ i ] = NULL;
                    orig_environ = env;
                }
            }
        }
        if (argc == 0) {
            return 1;
        }
        new_argc = argc + 2;
        new_argv = malloc(sizeof(char *) * (new_argc + 1));
        if (new_argv == NULL) {
            return 1;
        }
        new_argv[ 0 ] = EXECUTE;
        new_argv[ 1 ] = "--oom-pipe";
        sprintf(helper_num, "%d", pipes[ 1 ]);
        new_argv[ 2 ] = helper_num;
        for (i = 1;
                i <= (unsigned) argc;
                ++i) {
            new_argv[ i + 2 ] = argv[ i ];
        }
        if (orig_environ) {
            execve(EXECUTE, (char **)new_argv, orig_environ);
        } else {
            execv(EXECUTE, (char **)new_argv);
        }
        perror(EXECUTE);
        return 1;
    case 0: /* child, keep privileges and do the privileged work */
        close(pipes[ 1 ]);
        for (;;) {
            pid_t pid = 0;
            int ret = read(pipes[ 0 ], &pid, sizeof(pid_t));
            if (ret < 0 && errno == EINTR) {
                continue;
            }
            if (ret <= 0) { /* pipe closed or error, exit */
                _exit(0);
            }
            if (pid != 0) {
                if (set_protection(pid, 0)) {
                    kill(pid, SIGUSR1);
                }
            }
        }
    }
}

#else /* not Linux, the simple non-setuid case */

int main(int argc, char **argv)
{
    if (argc == 0) {
        return 1;
    }
    argv[0] = (char *)EXECUTE;
    execv(EXECUTE, argv);
    perror(EXECUTE);
    return 1;
}
#endif
