mm: fix overflow check in expand_upwards()

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.

Link: http://lkml.kernel.org/r/20170702192452.GA11868@p100.box
Fixes: bd726c90b6b8 ("Allow stack to grow up to address space limit")
Signed-off-by: Helge Deller <deller@gmx.de>
Reported-by: Jörn Engel <joern@purestorage.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/mmap.c b/mm/mmap.c
index 7fa6759322d1f2aa39f9dc2c497e714a8d9566f0..f19efcf7541878093eb3c3323a597cf8d1da5ae2 100644 (file)
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2231,7 +2231,7 @@ 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;