linux-kernel - [PATCH 3.2 46/74] mm: fix overflow check in expand

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Message-ID: <lsq.1507552234.67372650@decadent.org.uk>
Date:   Mon, 09 Oct 2017 13:30:34 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "Helge Deller" <deller@....de>,
        "Jörn Engel" <joern@...estorage.com>,
        "Hugh Dickins" <hughd@...gle.com>,
        "Oleg Nesterov" <oleg@...hat.com>,
        "Linus Torvalds" <torvalds@...ux-foundation.org>
Subject: [PATCH 3.2 46/74] mm: fix overflow check in expand_upwards()

3.2.94-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Helge Deller <deller@....de>

commit 37511fb5c91db93d8bd6e3f52f86e5a7ff7cfcdf upstream.

JÃ¶rn 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@....de>
Reported-by: Jörn Engel <joern@...estorage.com>
Cc: Hugh Dickins <hughd@...gle.com>
Cc: Oleg Nesterov <oleg@...hat.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 mm/mmap.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1717,7 +1717,7 @@ int expand_upwards(struct vm_area_struct
 
 	/* 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;