mm: fix overflow check in expand_upwards()

commit 37511fb5c91db93d8bd6e3f52f86e5a7ff7cfcdf upstream.

Jörn Engel noticed that the expand_upwards() function might not return
-ENOMEM in case the requested address is (unsigned long)-PAGE_SIZE and
if the architecture didn't defined TASK_SIZE as multiple of PAGE_SIZE.

Affected architectures are arm, frv, m68k, blackfin, h8300 and xtensa
which all define TASK_SIZE as 0xffffffff, but since none of those have
an upwards-growing stack we currently have no actual issue.

Nevertheless let's fix this just in case any of the architectures with
an upward-growing stack (currently parisc, metag and partly ia64) define
TASK_SIZE similar.

Change-Id: I70103edb3ab5ab871403dc35dcd382e44ecd3bb2
Link: http://lkml.kernel.org/r/[email protected]
Fixes: bd726c90b6b8 ("Allow stack to grow up to address space limit")
Signed-off-by: Helge Deller <[email protected]>
Reported-by: Jörn Engel <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: Oleg Nesterov <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
Signed-off-by: Ben Hutchings <[email protected]>
Signed-off-by: Francisco Franco <[email protected]>

mm/mmap.c

@@ -1780,7 +1780,7 @@ int expand_upwards(struct vm_area_struct *vma, unsigned long address)
 
 	/* Guard against exceeding limits of the address space. */
 	address &= PAGE_MASK;
-	if (address >= TASK_SIZE)
+	if (address >= (TASK_SIZE & PAGE_MASK))
 		return -ENOMEM;
 	address += PAGE_SIZE;