From: Rik van Riel <riel@xxxxxxxxxx>
Subject: mm: fix use-after-free in sys_remap_file_pages
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@xxxxxxxxxx>
Reported-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Cc: PaX Team <pageexec@xxxxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Michel Lespinasse <walken@xxxxxxxxxx>
Cc: Cyrill Gorcunov <gorcunov@xxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/fremap.c | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)
diff -puN mm/fremap.c~mm-fix-use-after-free-in-sys_remap_file_pages mm/fremap.c
--- a/mm/fremap.c~mm-fix-use-after-free-in-sys_remap_file_pages
+++ a/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 = ACCESS_ONCE(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
_
--
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