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From: Konstantin Belousov <kib@FreeBSD.org>
Date: Thu, 15 Jan 2009 12:15:46 +0000 (UTC)
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Subject: svn commit: r187298 - head/sys/kern
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Author: kib
Date: Thu Jan 15 12:15:46 2009
New Revision: 187298
URL: http://svn.freebsd.org/changeset/base/187298

Log:
  Lock the semaphore identifier lock during semaphore initialization to
  guarantee atomicity of the operation for other semaphore consumers.
  In particular, this should guard against access to the semaphore with
  not done or partially done MAC label assignment.
  
  Reviewed by:	rwatson
  MFC after:	1 month

Modified:
  head/sys/kern/sysv_sem.c

Modified: head/sys/kern/sysv_sem.c
==============================================================================
--- head/sys/kern/sysv_sem.c	Thu Jan 15 11:54:31 2009	(r187297)
+++ head/sys/kern/sysv_sem.c	Thu Jan 15 12:15:46 2009	(r187298)
@@ -914,6 +914,9 @@ semget(struct thread *td, struct semget_
 			goto done2;
 		}
 		DPRINTF(("semid %d is available\n", semid));
+		mtx_lock(&sema_mtx[semid]);
+		KASSERT((sema[semid].u.sem_perm.mode & SEM_ALLOC) == 0,
+		    ("Lost semaphore %d", semid));
 		sema[semid].u.sem_perm.key = key;
 		sema[semid].u.sem_perm.cuid = cred->cr_uid;
 		sema[semid].u.sem_perm.uid = cred->cr_uid;
@@ -932,6 +935,7 @@ semget(struct thread *td, struct semget_
 #ifdef MAC
 		mac_sysvsem_create(cred, &sema[semid]);
 #endif
+		mtx_unlock(&sema_mtx[semid]);
 		DPRINTF(("sembase = %p, next = %p\n",
 		    sema[semid].u.sem_base, &sem[semtot]));
 	} else {