kern/118153: [fix] "semprt" can be invalid after wakeup in the semop()

[Ivan Shcheklein]

>Number:         118153
>Category:       kern
>Synopsis:       [fix] "semprt" can be invalid after wakeup in the semop()
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    freebsd-bugs
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Tue Nov 20 16:30:01 UTC 2007
>Closed-Date:
>Last-Modified:
>Originator:     Ivan Shcheklein
>Release:        FREEBSD-6.2
>Organization:
ISP RAS
>Environment:
FreeBSD 6.2-RELEASE i386
>Description:
Fistly, sorry for the my previous post of this bug:
http://lists.freebsd.org/pipermail/freebsd-bugs/2007-November/026847.html

I didn't know about the better way to submit bugs. I think, it can be removed or marked as duplicate to this one.

The buf itself is the following.

In sysv_sem.c::1173 we have:

                /* ... semaphores wakes up ... */
		
                if (sopptr->sem_op == 0)
			semptr->semzcnt--;
		else
			semptr->semncnt--;

Used here "semptr" after wakeup can be invalid due to "semakptr->u.sem_base" can be changed during semaphore sleeping. (For example it can be changed by removing another semaphore).

>How-To-Repeat:


>Fix:
The solution for this problem is quiet obvious. We must use "semakptr" to get new "semptr". For example (possibly it can be written better):

                if (sopptr->sem_op == 0)
			(&semakptr->u.sem_base[sopptr->sem_num])->semzcnt--;
		else
			(&semakptr->u.sem_base[sopptr->sem_num])->semncnt--;

>Release-Note:
>Audit-Trail:
>Unformatted: