From f7cd45464fd7c037f6a60098ae77760998b3b4b6 Mon Sep 17 00:00:00 2001
From: Simon Rettberg
Date: Fri, 10 May 2019 15:25:43 +0200
Subject: Initial commit

---
 src/util.c | 187 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 187 insertions(+)
 create mode 100644 src/util.c

(limited to 'src/util.c')

diff --git a/src/util.c b/src/util.c
new file mode 100644
index 0000000..e9d642c
--- /dev/null
+++ b/src/util.c
@@ -0,0 +1,187 @@
+#include "util.h"
+#include "userlist.h"
+
+#include <string.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <errno.h>
+#include <unistd.h>
+#include <stdarg.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <sys/stat.h>
+#include <signal.h>
+#include <pwd.h>
+#include <poll.h>
+
+int _testmode = 0;
+
+// Base time for monotonic clock
+static struct timespec basetime;
+
+time_t now()
+{
+    struct timespec retval;
+    if ( clock_gettime( CLOCK_MONOTONIC, &retval ) == -1 ) {
+        perror( "Cannot clock_gettime CLOCK_MONOTONIC" );
+        abort();
+    }
+    return (time_t)( retval.tv_sec - basetime.tv_sec );
+}
+
+void init_time()
+{
+    if ( clock_gettime( CLOCK_MONOTONIC, &basetime ) == -1 ) {
+        perror( "cannot clock_gettime CLOCK_MONOTONIC" );
+        basetime.tv_sec = 0; // Hope it doesn't overflow
+    }
+}
+
+/**
+ * Return false = parent, true = second child
+ */
+bool doublefork()
+{
+    const pid_t c1 = fork();
+    if ( c1 == -1 ) {
+        perror( "doublefork: First fork failed" );
+        return false;
+    }
+    if ( c1 != 0 ) {
+        // Parent (main program)
+        int ws;
+        while ( waitpid( c1, &ws, 0 ) == -1 && errno == EINTR ) {}
+        return false;
+    }
+    // This is executed by first child
+    signal( SIGCHLD, SIG_IGN );
+    // Fork again
+    const pid_t c2 = fork();
+    if ( c2 == -1 ) {
+        perror( "doublefork: Second fork failed" );
+        abort();
+    }
+    if ( c2 != 0 ) {
+        // Second parent (first child), exit immediately
+        exit( 0 );
+    }
+    // Second child, this is what we want
+    signal( SIGCHLD, SIG_DFL );
+    return true;
+}
+
+bool waitRead( int fd, int ms )
+{
+    struct pollfd pd = { .fd = fd, .events = POLLIN | POLLHUP | POLLRDHUP };
+    return poll( &pd, 1, ms ) > 0 && ( pd.revents & POLLIN ) != 0;
+}
+
+void copy( const char *src, char *dst, size_t len, const char *stop )
+{
+    const char *end = src + len - 1;
+    while ( src < end && *src != '\0' && ( stop == NULL || strchr( stop, *src ) == NULL ) ) {
+        *dst++ = *src++;
+    }
+    *dst = '\0';
+}
+
+void killSession( const struct user * user )
+{
+    if ( _testmode ) {
+        printf( "Not really killing session %s of user %s.\n", user->sessionName, user->user );
+        return;
+    }
+    if ( ! doublefork() )
+        return;
+    // Async do NOT use return from here on
+    if ( user->sessionName[0] != '\0' ) {
+        printf( "Terminating session %s of %s.\n", user->sessionName, user->user );
+        run( true, "loginctl", "terminate-session", user->sessionName );
+        sleep( 5 );
+        if ( kill( user->sessionLeader, 0 ) == -1
+                && ( user->sessionHead == 0 || kill( user->sessionHead, 0 ) == -1 ) )
+            exit( 0 );
+    }
+    if ( user->sessionHead != 0 && kill( user->sessionHead, SIGTERM ) == 0 ) {
+        printf( "Session %s seems not entirely dead, TERMing loginpid %d...\n", user->sessionName, (int)user->sessionHead );
+        sleep( 2 );
+    }
+    if ( ( killpg( user->sessionLeader, SIGTERM ) & kill( user->sessionLeader, SIGTERM ) ) == 0 ) {
+        printf( "Session %s seems not entirely dead, TERMing process group %d...\n", user->sessionName, (int)user->sessionLeader );
+        sleep( 3 );
+    }
+    // Maybe we need KILL now...
+    if ( user->sessionHead != 0 && kill( user->sessionHead, SIGKILL ) == 0 ) {
+        printf( "Session %s seems not entirely dead, KILLing %d...\n", user->sessionName, (int)user->sessionHead );
+    }
+    exit( 0 );
+}
+
+void redirect( int newIn, int newOut )
+{
+    if ( newIn > 2 ) {
+        dup2( newIn, STDIN_FILENO );
+        close( newIn );
+    }
+    if ( newOut > 2 ) {
+        dup2( newOut, STDOUT_FILENO );
+        close( newOut );
+    }
+}
+
+void switchUserSafe( const char* user )
+{
+    errno = 0;
+    struct passwd *u = getpwnam( user );
+    if ( u == NULL ) {
+        if ( errno != 0 ) {
+            perror( "switchUserSafe: Cannot switch to user" );
+        } else {
+            fprintf( stderr, "switchUserSafe: Cannot switch to user %s: User not known.\n", user );
+        }
+        exit( 1 );
+    }
+    chdir( "/" );
+    if ( setgid( u->pw_gid ) != 0 ) {
+        perror( "switchUserSafe: setgid failed" );
+        exit( 1 );
+    }
+    if ( setuid( u->pw_uid ) != 0 ) {
+        perror( "switchUserSafe: setuid failed" );
+        exit( 1 );
+    }
+    if ( u->pw_dir == NULL ) {
+        unsetenv( "HOME" );
+    } else {
+        setenv( "HOME", u->pw_dir, 1 );
+    }
+    setenv( "USER", u->pw_name, 1 );
+}
+
+void run( bool detach, const char *file, ... )
+{
+    if ( detach && ! doublefork() )
+        return;
+    char *argv[100];
+    argv[0] = strdup( file );
+    argv[99] = NULL;
+    va_list ap;
+    va_start( ap, file );
+    for ( int i = 1; i < 99; ++i ) {
+        argv[i] = va_arg( ap, char* );
+        if ( argv[i] == NULL )
+            break;
+        argv[i] = strdup( argv[i] );
+    }
+    va_end( ap );
+    printf( "Running: '%s'", file );
+    for ( int i = 0; i < 100 && argv[i] != NULL; ++i ) {
+        printf( " '%s'", argv[i] );
+    }
+    printf( "\n" );
+    execvp( strdup( file ), argv );
+    // Something went wrong...
+    perror( "run execvp failed" );
+    exit( 1 );
+}
+
-- 
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