[3.11.y.z extended stable] Patch "mm: fix use-after-free in sys_remap_file_pages" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    mm: fix use-after-free in sys_remap_file_pages

to the linux-3.11.y-queue branch of the 3.11.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.11.y-queue

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.11.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From 894334db25a93583b6502e3228b1995ebd221cc4 Mon Sep 17 00:00:00 2001
From: Rik van Riel <riel at redhat.com>
Date: Thu, 2 Jan 2014 12:58:46 -0800
Subject: mm: fix use-after-free in sys_remap_file_pages

commit 4eb919825e6c3c7fb3630d5621f6d11e98a18b3a upstream.

remap_file_pages calls mmap_region, which may merge the VMA with other
existing VMAs, and free "vma".  This can lead to a use-after-free bug.
Avoid the bug by remembering vm_flags before calling mmap_region, and
not trying to dereference vma later.

Signed-off-by: Rik van Riel <riel at redhat.com>
Reported-by: Dmitry Vyukov <dvyukov at google.com>
Cc: PaX Team <pageexec at freemail.hu>
Cc: Kees Cook <keescook at chromium.org>
Cc: Michel Lespinasse <walken at google.com>
Cc: Cyrill Gorcunov <gorcunov at openvz.org>
Cc: Hugh Dickins <hughd at google.com>
Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 mm/fremap.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/mm/fremap.c b/mm/fremap.c
index 5bff081..bbc4d66 100644
--- a/mm/fremap.c
+++ b/mm/fremap.c
@@ -208,9 +208,10 @@ get_write_lock:
 		if (mapping_cap_account_dirty(mapping)) {
 			unsigned long addr;
 			struct file *file = get_file(vma->vm_file);
+			/* mmap_region may free vma; grab the info now */
+			vm_flags = vma->vm_flags;

-			addr = mmap_region(file, start, size,
-					vma->vm_flags, pgoff);
+			addr = mmap_region(file, start, size, vm_flags, pgoff);
 			fput(file);
 			if (IS_ERR_VALUE(addr)) {
 				err = addr;
@@ -218,7 +219,7 @@ get_write_lock:
 				BUG_ON(addr != start);
 				err = 0;
 			}
-			goto out;
+			goto out_freed;
 		}
 		mutex_lock(&mapping->i_mmap_mutex);
 		flush_dcache_mmap_lock(mapping);
@@ -253,6 +254,7 @@ get_write_lock:
 out:
 	if (vma)
 		vm_flags = vma->vm_flags;
+out_freed:
 	if (likely(!has_write_lock))
 		up_read(&mm->mmap_sem);
 	else
--
1.8.3.2