[ 43/50] ipc, shm: guard against non-existant vma in shmdt(2)

[Greg Kroah-Hartman]

3.11-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Davidlohr Bueso <davidlohr.bueso@xxxxxx>

commit 530fcd16d87cd2417c472a581ba5a1e501556c86 upstream.

When !CONFIG_MMU there's a chance we can derefence a NULL pointer when the
VM area isn't found - check the return value of find_vma().

Also, remove the redundant -EINVAL return: retval is set to the proper
return code and *only* changed to 0, when we actually unmap the segments.

Signed-off-by: Davidlohr Bueso <davidlohr.bueso@xxxxxx>
Cc: Sedat Dilek <sedat.dilek@xxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Cc: Manfred Spraul <manfred@xxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Mike Galbraith <efault@xxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 ipc/shm.c |    3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -1295,8 +1295,7 @@ SYSCALL_DEFINE1(shmdt, char __user *, sh
 #else /* CONFIG_MMU */
 	/* under NOMMU conditions, the exact address to be destroyed must be
 	 * given */
-	retval = -EINVAL;
-	if (vma->vm_start == addr && vma->vm_ops == &shm_vm_ops) {
+	if (vma && vma->vm_start == addr && vma->vm_ops == &shm_vm_ops) {
 		do_munmap(mm, vma->vm_start, vma->vm_end - vma->vm_start);
 		retval = 0;
 	}


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