[BUGFIX][PATCH] shmdt cannot detach not-alined shm segment cleanly.

[BUGFIX][PATCH] shmdt cannot detach not-alined shm segment cleanly.

[KAMEZAWA Hiroyuki]

This is a patch for a problem of shmdt().
It is found by a test, not a serious problem.
-- Kame

sys_shmdt() can manages shm segments which is covered by multiple vmas.
(This can happen when a user uses mprotect() after shmat().)

This works well if shm is aligned to PAGE_SIZE, but if not, the last segment
cannot be detached. It is because a comparison in sys_shmdt()

	(vma->vm_end - addr) < size
		addr == return address of shmat()
		size == shmsize, argments to shmget()

size should be aligned to PAGE_SIZE before being compared with vma->vm_end,
which is aligned.

Signed-Off-By:KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>

Index: linux-2.6.16-rc2.org/ipc/shm.c
===================================================================
--- linux-2.6.16-rc2.org.orig/ipc/shm.c
+++ linux-2.6.16-rc2.org/ipc/shm.c
@@ -870,6 +870,7 @@ asmlinkage long sys_shmdt(char __user *s
  	 * could possibly have landed at. Also cast things to loff_t to
  	 * prevent overflows and make comparisions vs. equal-width types.
  	 */
+	size = PAGE_ALIGN(size);
  	while (vma && (loff_t)(vma->vm_end - addr) <= size) {
  		next = vma->vm_next;