[PATCH 3/3] vm: fix vm_pgoff wrap in upward expansion - CVE-2011-2496

[Paolo Pisati]

Commit a626ca6a6564 ("vm: fix vm_pgoff wrap in stack expansion") fixed
the case of an expanding mapping causing vm_pgoff wrapping when you had
downward stack expansion.  But there was another case where IA64 and
PA-RISC expand mappings: upward expansion.

This fixes that case too.

BugLink: http://bugs.launchpad.net/bugs/869243

commit upstream 42c36f63ac1366ab0ecc2d5717821362c259f517

Signed-off-by: Hugh Dickins <hughd at google.com>
Cc: stable at kernel.org
Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>

Signed-off-by: Paolo Pisati <paolo.pisati at canonical.com>
---
 mm/mmap.c |    9 ++++++---
 1 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/mm/mmap.c b/mm/mmap.c
index dcd3dcc..b0d5d58 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1600,9 +1600,12 @@ int expand_upwards(struct vm_area_struct *vma, unsigned long address)
 		size = address - vma->vm_start;
 		grow = (address - vma->vm_end) >> PAGE_SHIFT;
 
-		error = acct_stack_growth(vma, size, grow);
-		if (!error)
-			vma->vm_end = address;
+		error = -ENOMEM;
+		if (vma->vm_pgoff + (size >> PAGE_SHIFT) >= vma->vm_pgoff) {
+			error = acct_stack_growth(vma, size, grow);
+			if (!error)
+				vma->vm_end = address;
+		}
 	}
 	anon_vma_unlock(vma);
 	return error;
-- 
1.7.5.4