[PATCH] mm: fix use-after-free in sys_remap_file_pages

[Kees Cook]

From: PaX Team <pageexec@xxxxxxxxxxx>

http://lkml.org/lkml/2013/9/17/30

SyS_remap_file_pages() calls mmap_region(), which calls remove_vma_list(),
which calls remove_vma(), which frees the vma.  Later (after out label)
SyS_remap_file_pages() accesses the freed vma in vm_flags = vma->vm_flags.

Reported-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Signed-off-by: PaX Team <pageexec@xxxxxxxxxxx>
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
---
 mm/fremap.c |    2 ++
 1 file changed, 2 insertions(+)

diff --git a/mm/fremap.c b/mm/fremap.c
index 5bff08147768..afad07b85ef2 100644
--- a/mm/fremap.c
+++ b/mm/fremap.c
@@ -218,6 +218,8 @@ get_write_lock:
 				BUG_ON(addr != start);
 				err = 0;
 			}
+			vm_flags = vma->vm_flags;
+			vma = NULL;
 			goto out;
 		}
 		mutex_lock(&mapping->i_mmap_mutex);
-- 
1.7.9.5


-- 
Kees Cook
Chrome OS Security
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