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Date: 14 Jan 2003 08:16:19 -0000
Message-ID: <20030114081619.5918.qmail@nagoya.betaversion.org>
From: bugzilla@apache.org
To: bugs@httpd.apache.org
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Subject: DO NOT REPLY [Bug 16056] New:  -
    Shared memory & mutex ownership not correctly established for SysV
 mutexes.

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http://nagoya.apache.org/bugzilla/show_bug.cgi?id=16056

Shared memory & mutex ownership not correctly established for SysV mutexes.

           Summary: Shared memory & mutex ownership not correctly
                    established for SysV mutexes.
           Product: APR
           Version: HEAD
          Platform: Other
        OS/Version: Linux
            Status: NEW
          Severity: Major
          Priority: Other
         Component: APR
        AssignedTo: bugs@httpd.apache.org
        ReportedBy: achowe@snert.com


While attempting to port mod_watch to Apache 2.0, which uses both anonymous
shared memory and mutexes, I found that I kept getting EACCESS every time I
tried to lock the mutex. Now comparing my shared memory and mutex code used in
1.3 vs. that in the APR, the only difference I could find was that the APR code
fails to assign the uid/gid ownership of the mutex to that of the "prefork"
child processes (User/Group directives). Now the APR has no appropriate API for
changing the ownership of shared memory or a mutex.  

I tested my theory by adding the following code to my module, which proceeded to
function afterwards:

#if defined(APR_USE_SHMEM_SHMGET) || defined(APR_USE_SHMEM_SHMGET_ANON)
#include "arch/unix/shm.h"
#include "unixd.h"
#endif

#if defined(APR_HAS_SYSVSEM_SERIALIZE)
#include "arch/unix/global_mutex.h"
#include "unixd.h"
#endif

...

  rc = apr_shm_create((apr_shm_t **) &tp->shared, bytes, (const char *) 0, p);
  if (rc != APR_SUCCESS)
	goto error0;

#if defined(APR_USE_SHMEM_SHMGET) || defined(APR_USE_SHMEM_SHMGET_ANON)
/* Setup the access permissions for the shared memory so that child processes
 * that change their user/group can still access the shared memory after. This
 * should have been done in the APR library or (due to lack of clear
 * documentation) I'm misundestanding how anonymous mutexes and shared
 * memory work.
 */
{
	struct shmid_ds shmbuf;
        apr_shm_t *theMem = tp->shared;

        if (shmctl(theMem->shmid, IPC_STAT, &shmbuf) != 0)
                goto error1;
        shmbuf.shm_perm.uid = unixd_config.user_id;;
        shmbuf.shm_perm.gid = unixd_config.group_id;
        shmbuf.shm_perm.mode = 0600;
        if (shmctl(theMem->shmid, IPC_SET, &shmbuf) != 0)
                goto error1;
}
#endif

...

	rc = apr_global_mutex_create(
		(apr_global_mutex_t **) &tp->mutex,
		tp->lockfile, APR_LOCK_DEFAULT, p
	);
	if (rc != APR_SUCCESS)
		goto error1;

#if defined(APR_HAS_SYSVSEM_SERIALIZE)
/* || defined(APR_HAS_FCNTL_SERIALIZE) || defined(APR_HAS_FLOCK_SERIALIZE) */
/* Setup the access permissions for the mutex so that child processes
 * that change their user/group can still access the mutex after. This
 * should have been done in the APR library or (due to lack of clear
 * documentation) I'm misundestanding how anonymous mutexes and shared
 * memory work.
 */
{
        union semun ick;
        struct semid_ds sembuf;
        apr_global_mutex_t *theMutex = tp->mutex;

        ick.buf = &sembuf;
        if (semctl(theMutex->proc_mutex->interproc->filedes, 0, IPC_STAT, ick) != 0)
                goto error3;
        sembuf.sem_perm.uid = unixd_config.user_id;
        sembuf.sem_perm.gid = unixd_config.group_id;
        sembuf.sem_perm.mode = 0600;
        if (semctl(theMutex->proc_mutex->interproc->filedes, 0, IPC_SET, ick) != 0)
                goto error3;
}
#endif

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