9c30d4c2f8
When sesman used a standard TCP socket, we were guaranteed only one copy of sesman could run on on address, as standard TCP listening rules enforced this. This isn't the case with Unix Domain sockets. This module implements a locking mechanism for a UDS which emulates the standard TCP socket behaviour.
147 lines
4.0 KiB
C
147 lines
4.0 KiB
C
/**
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* xrdp: A Remote Desktop Protocol server.
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*
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* Copyright (C) 2022 Matt Burt, all xrdp contributors
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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/**
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*
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* @file lock_uds.c
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* @brief Providing a locking facility for Unix Domain Sockets
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* @author Matt Burt
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*
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* It is difficult for a server to determine whether a socket it wishes
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* to listen on is already active or not. The purpose of this module is to
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* provide a locking facility which can be used as a proxy for this.
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*/
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#if defined(HAVE_CONFIG_H)
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#include <config_ac.h>
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#endif
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#include "arch.h"
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#include "os_calls.h"
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#include "string_calls.h"
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#include "log.h"
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#include "lock_uds.h"
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struct lock_uds
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{
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char *filename; ///<< Name of the lock file
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int fd; ///<< File decriptor for open file
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int pid; ///<< PID of process originally taking out lock
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};
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/******************************************************************************/
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struct lock_uds *
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lock_uds(const char *sockname)
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{
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struct lock_uds *lock = NULL;
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char *filename = NULL;
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int fd = -1;
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if (sockname == NULL || sockname[0] != '/')
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{
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LOG_DEVEL(LOG_LEVEL_ERROR, "Invalid sockname '%s'",
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(sockname == NULL) ? "<null>" : sockname);
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}
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else
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{
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/* Allocate space for lock filename and result */
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filename = (char *)g_malloc(g_strlen(sockname) + 1 + 5 + 1, 0);
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lock = g_new0(struct lock_uds, 1);
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if (lock == NULL || filename == NULL)
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{
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LOG(LOG_LEVEL_ERROR, "%s : Out of memory", __func__);
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}
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else
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{
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int saved_umask;
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/* Construct the filename */
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/* This call is guaranteed to succeed as we know that sockname
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* contains at least one '/' */
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char *p = filename;
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const char *basename = g_strrchr(sockname, '/') + 1;
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g_memcpy(p, sockname, basename - sockname);
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p += basename - sockname;
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*p++ = '.';
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g_strcpy(p, basename);
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p += g_strlen(p);
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*p++ = '.';
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*p++ = 'l';
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*p++ = 'o';
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*p++ = 'c';
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*p++ = 'k';
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*p++ = '\0';
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saved_umask = g_umask_hex(0x77);
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fd = g_file_open(filename);
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g_umask_hex(saved_umask);
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if (fd < 0)
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{
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LOG(LOG_LEVEL_ERROR, "Unable to create '%s' [%s]",
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filename, g_get_strerror());
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}
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else if (g_file_lock(fd, 0, 0) == 0)
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{
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LOG(LOG_LEVEL_ERROR, "Unable to get lock for '%s' - "
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"program already running?", sockname);
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g_file_close(fd);
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fd = -1;
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}
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}
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}
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if (fd >= 0)
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{
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/* Success - finish off */
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lock->filename = filename;
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lock->fd = fd;
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lock->pid = g_getpid();
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}
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else
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{
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g_free(filename);
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g_free(lock);
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lock = NULL;
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}
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return lock;
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}
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/******************************************************************************/
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void
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unlock_uds(struct lock_uds *lock)
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{
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if (lock != NULL)
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{
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if (lock->fd >= 0)
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{
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g_file_close(lock->fd);
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lock->fd = -1; // In case of use-after-free
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}
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/* Only delete the lock file if we are the process which
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* created it */
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if (g_getpid() == lock->pid)
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{
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g_file_delete(lock->filename);
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}
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g_free(lock->filename);
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lock->filename = NULL;
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g_free(lock);
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}
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}
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