[PATCH 4.19 202/280] mm/memory.c: do_fault: avoid usage of stale vm_area_struct

From: Greg Kroah-Hartman
Date: Fri Mar 22 2019 - 08:06:54 EST

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


From: Jan Stancek <jstancek@xxxxxxxxxx>

commit fc8efd2ddfed3f343c11b693e87140ff358d7ff5 upstream.

LTP testcase mtest06 [1] can trigger a crash on s390x running 5.0.0-rc8.
This is a stress test, where one thread mmaps/writes/munmaps memory area
and other thread is trying to read from it:

CPU: 0 PID: 2611 Comm: mmap1 Not tainted 5.0.0-rc8+ #51
Hardware name: IBM 2964 N63 400 (z/VM 6.4.0)
Krnl PSW : 0404e00180000000 00000000001ac8d8 (__lock_acquire+0x7/0x7a8)
Call Trace:
([<0000000000000000>] (null))
[<00000000001adae4>] lock_acquire+0xec/0x258
[<000000000080d1ac>] _raw_spin_lock_bh+0x5c/0x98
[<000000000012a780>] page_table_free+0x48/0x1a8
[<00000000002f6e54>] do_fault+0xdc/0x670
[<00000000002fadae>] __handle_mm_fault+0x416/0x5f0
[<00000000002fb138>] handle_mm_fault+0x1b0/0x320
[<00000000001248cc>] do_dat_exception+0x19c/0x2c8
[<000000000080e5ee>] pgm_check_handler+0x19e/0x200

page_table_free() is called with NULL mm parameter, but because "0" is a
valid address on s390 (see S390_lowcore), it keeps going until it
eventually crashes in lockdep's lock_acquire. This crash is
reproducible at least since 4.14.

Problem is that "vmf->vma" used in do_fault() can become stale. Because
mmap_sem may be released, other threads can come in, call munmap() and
cause "vma" be returned to kmem cache, and get zeroed/re-initialized and

handle_mm_fault |
__handle_mm_fault |
do_fault |
vma = vmf->vma |
do_read_fault |
__do_fault |
vma->vm_ops->fault(vmf); |
mmap_sem is released |
| do_munmap()
| remove_vma_list()
| remove_vma()
| vm_area_free()
| # vma is released
| ...
| # same vma is allocated
| # from kmem cache
| do_mmap()
| vm_area_alloc()
| memset(vma, 0, ...)
pte_free(vma->vm_mm, ...); |
page_table_free |
<crash> |

Cache mm_struct to avoid using potentially stale "vma".

[1] https://github.com/linux-test-project/ltp/blob/master/testcases/kernel/mem/mtest06/mmap1.c

Link: http://lkml.kernel.org/r/5b3fdf19e2a5be460a384b936f5b56e13733f1b8.1551595137.git.jstancek@xxxxxxxxxx
Signed-off-by: Jan Stancek <jstancek@xxxxxxxxxx>
Reviewed-by: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Reviewed-by: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Acked-by: Rafael Aquini <aquini@xxxxxxxxxx>
Reviewed-by: Minchan Kim <minchan@xxxxxxxxxx>
Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Huang Ying <ying.huang@xxxxxxxxx>
Cc: Souptick Joarder <jrdr.linux@xxxxxxxxx>
Cc: Jerome Glisse <jglisse@xxxxxxxxxx>
Cc: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

mm/memory.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)

--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3762,10 +3762,13 @@ static vm_fault_t do_shared_fault(struct
* but allow concurrent faults).
* The mmap_sem may have been released depending on flags and our
* return value. See filemap_fault() and __lock_page_or_retry().
+ * If mmap_sem is released, vma may become invalid (for example
+ * by other thread calling munmap()).
static vm_fault_t do_fault(struct vm_fault *vmf)
struct vm_area_struct *vma = vmf->vma;
+ struct mm_struct *vm_mm = vma->vm_mm;
vm_fault_t ret;

@@ -3806,7 +3809,7 @@ static vm_fault_t do_fault(struct vm_fau

/* preallocated pagetable is unused: free it */
if (vmf->prealloc_pte) {
- pte_free(vma->vm_mm, vmf->prealloc_pte);
+ pte_free(vm_mm, vmf->prealloc_pte);
vmf->prealloc_pte = NULL;
return ret;