lkml.org 
[lkml]   [2007]   [Nov]   [16]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Subject[PATCH 1/3] mmap: protect from stack expantion into low vm addresses
From
Date
When adding the new security hooks into mmap to enhance protection
against NULL pointers in the kernel I overlooked that a user may be able
to expand the stack all the way down to low addresses. This flaw was
pointed out by a PaX/grsecurity developer and this patch should provide
protection against this missed code path.

Signed-off-by: Eric Paris <eparis@redhat.com>

---
** Be very careful applying/rediffing this patch. Standard 3 lines of
context from git diff will misapply the first hunk to expand_upwards
instead of properly in expand_downwards. This patch was generated using
-U 4 to make sure it applies in the correct place. **

mm/mmap.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)
--- kernel-1/mm/mmap.c
+++ kernel-2/mm/mmap.c
@@ -1614,17 +1614,21 @@ static inline int expand_downwards(struc
* so that the anon_vma locking is not a noop.
*/
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);

/*
* vma->vm_start/vm_end cannot change under us because the caller
* 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) {
unsigned long size, grow;

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2007-11-16 21:59    [from the cache]
©2003-2011 Jasper Spaans