linux-kernel - [PATCH 3.11 098/208] mm: fix use-after-free in sys_remap_file

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Message-Id: <1389628849-1614-99-git-send-email-luis.henriques@canonical.com>
Date:	Mon, 13 Jan 2014 15:58:59 +0000
From:	Luis Henriques <luis.henriques@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Rik van Riel <riel@...hat.com>, PaX Team <pageexec@...email.hu>,
	Kees Cook <keescook@...omium.org>,
	Michel Lespinasse <walken@...gle.com>,
	Cyrill Gorcunov <gorcunov@...nvz.org>,
	Hugh Dickins <hughd@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Luis Henriques <luis.henriques@...onical.com>
Subject: [PATCH 3.11 098/208] mm: fix use-after-free in sys_remap_file_pages

3.11.10.3 -stable review patch.  If anyone has any objections, please let me know.

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

From: Rik van Riel <riel@...hat.com>

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@...hat.com>
Reported-by: Dmitry Vyukov <dvyukov@...gle.com>
Cc: PaX Team <pageexec@...email.hu>
Cc: Kees Cook <keescook@...omium.org>
Cc: Michel Lespinasse <walken@...gle.com>
Cc: Cyrill Gorcunov <gorcunov@...nvz.org>
Cc: Hugh Dickins <hughd@...gle.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Luis Henriques <luis.henriques@...onical.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

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