[patch 57/73] security: protect from stack expantion into low vmaddresses

[Greg KH]

2.6.23-stable review patch.  If anyone has any objections, please let us know.
------------------
From: Eric Paris <eparis@xxxxxxxxxx>

patch 8869477a49c3e99def1fcdadd6bbc407fea14b45 in mainline.

Add security checks to make sure we are not attempting to expand the
stack into memory protected by mmap_min_addr

Signed-off-by: Eric Paris <eparis@xxxxxxxxxx>
Signed-off-by: James Morris <jmorris@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>

---
 mm/mmap.c |    8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1619,6 +1619,12 @@ static inline int expand_downwards(struc
 	 */
 	if (unlikely(anon_vma_prepare(vma)))
 		return -ENOMEM;
+
+	address &= PAGE_MASK;
+	error = security_file_mmap(0, 0, 0, 0, address, 1);
+	if (error)
+		return error;
+
 	anon_vma_lock(vma);
 
 	/*
@@ -1626,8 +1632,6 @@ static inline int expand_downwards(struc
 	 * is required to hold the mmap_sem in read mode.  We need the
 	 * anon_vma lock to serialize against concurrent expand_stacks.
 	 */
-	address &= PAGE_MASK;
-	error = 0;
 
 	/* Somebody else might have raced and expanded it already */
 	if (address < vma->vm_start) {

-- 
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