150 lines
4.8 KiB
C
150 lines
4.8 KiB
C
/****************************************************************************
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* apps/fsutils/passwd/passwd_lock.c
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*
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* Copyright (C) 2016 Gregory Nutt. All rights reserved.
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* Author: Gregory Nutt <gnutt@nuttx.org>
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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*
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in
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* the documentation and/or other materials provided with the
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* distribution.
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* 3. Neither the name NuttX nor the names of its contributors may be
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* used to endorse or promote products derived from this software
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
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* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
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* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
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* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
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* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
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* OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
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* AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
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* ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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* POSSIBILITY OF SUCH DAMAGE.
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*
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****************************************************************************/
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/****************************************************************************
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* Included Files
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****************************************************************************/
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#include <semaphore.h>
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#include <assert.h>
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#include <errno.h>
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#include "passwd.h"
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/****************************************************************************
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* Pre-processor Definitions
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****************************************************************************/
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#ifdef CONFIG_FS_NAMED_SEMAPHORES
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/* In the kernel build mode, we need to use a named semaphore so that all
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* processes will share the same, named semaphore instance.
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*/
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# define PASSWD_SEMNAME "pwsem" /* Global named semaphore */
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#endif
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/****************************************************************************
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* Private Data
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****************************************************************************/
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#ifndef CONFIG_FS_NAMED_SEMAPHORES
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/* In the FLAT and PROTECTED build modes, we do not need to bother with a
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* named semaphore. We use a single global semaphore in theses cases.
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*/
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static sem_t g_passwd_sem = SEM_INITIALIZER(1);
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#endif
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/****************************************************************************
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* Public Functions
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****************************************************************************/
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/****************************************************************************
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* Name: passwd_lock
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*
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* Description:
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* Lock the /etc/passwd file. This is not a real lock at the level of the
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* file system. Rather, it only prevents concurrent modification of the
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* /etc/passwd file by passwd_adduser(), passwd_deluser(), and
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* passwd_update(). Other accesses to /etc/passwd could still cause
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* concurrency problem and file corruption.
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*
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* Input Parameters:
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*
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* Returned Value:
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* Zero (OK) is returned on success; a negated errno value is returned on
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* failure.
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*
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****************************************************************************/
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int passwd_lock(FAR sem_t **semp)
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{
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FAR sem_t *sem;
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#ifdef CONFIG_FS_NAMED_SEMAPHORES
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/* Open the shared, named semaphore */
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sem = sem_open(PASSWD_SEMNAME, O_CREAT, 0644, 1);
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if (sem == SEM_FAILED)
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{
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int errcode = errno;
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DEBUGASSERT(errcode > 0);
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return -errcode;
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}
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#else
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/* Use the global semaphore */
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sem = &g_passwd_sem;
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#endif
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/* Take the semaphore. Only EINTR errors are expected. */
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while (sem_wait(sem) < 0)
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{
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int errcode = errno;
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DEBUGASSERT(errcode == EINTR || errcode == ECANCELED);
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UNUSED(errcode);
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}
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*semp = sem;
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return OK;
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}
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/****************************************************************************
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* Name: passwd_unlock
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*
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* Description:
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* Undo the work done by passwd_lock.
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*
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* Input Parameters:
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* sem Pointer to the semaphore
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*
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* Returned Value:
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* None
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*
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****************************************************************************/
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void passwd_unlock(FAR sem_t *sem)
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{
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/* Release our count on the semaphore */
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sem_post(sem);
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#ifdef CONFIG_FS_NAMED_SEMAPHORES
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/* Close the named semaphore */
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sem_close(sem);
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#endif
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}
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