Commit 49251910 authored by Minchan Kim's avatar Minchan Kim Committed by Greg Kroah-Hartman

android: binder: fix the race mmap and alloc_new_buf_locked

commit da1b9564 upstream.

There is RaceFuzzer report like below because we have no lock to close
below the race between binder_mmap and binder_alloc_new_buf_locked.
To close the race, let's use memory barrier so that if someone see
alloc->vma is not NULL, alloc->vma_vm_mm should be never NULL.

(I didn't add stable mark intentionallybecause standard android
userspace libraries that interact with binder (libbinder & libhwbinder)
prevent the mmap/ioctl race. - from Todd)

Thread interleaving:
CPU0 (binder_alloc_mmap_handler)              CPU1 (binder_alloc_new_buf_locked)
=====                                         =====
// drivers/android/binder_alloc.c
// #L718 (v4.18-rc3)
alloc->vma = vma;
                                              // drivers/android/binder_alloc.c
                                              // #L346 (v4.18-rc3)
                                              if (alloc->vma == NULL) {
                                                  // alloc->vma is not NULL at this point
                                                  return ERR_PTR(-ESRCH);
                                              // #L438
                                              binder_update_page_range(alloc, 0,
                                                      (void *)PAGE_ALIGN((uintptr_t)buffer->data),

                                              // In binder_update_page_range() #L218
                                              // But still alloc->vma_vm_mm is NULL here
                                              if (need_mm && mmget_not_zero(alloc->vma_vm_mm))
alloc->vma_vm_mm = vma->vm_mm;

Crash Log:
BUG: KASAN: null-ptr-deref in __atomic_add_unless include/asm-generic/atomic-instrumented.h:89 [inline]
BUG: KASAN: null-ptr-deref in atomic_add_unless include/linux/atomic.h:533 [inline]
BUG: KASAN: null-ptr-deref in mmget_not_zero include/linux/sched/mm.h:75 [inline]
BUG: KASAN: null-ptr-deref in binder_update_page_range+0xece/0x18e0 drivers/android/binder_alloc.c:218
Write of size 4 at addr 0000000000000058 by task syz-executor0/11184

CPU: 1 PID: 11184 Comm: syz-executor0 Not tainted 4.18.0-rc3 #1
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.8.2-0-g33fbe13 by 04/01/2014
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x16e/0x22c lib/dump_stack.c:113
 kasan_report_error mm/kasan/report.c:352 [inline]
 kasan_report+0x163/0x380 mm/kasan/report.c:412
 check_memory_region_inline mm/kasan/kasan.c:260 [inline]
 check_memory_region+0x140/0x1a0 mm/kasan/kasan.c:267
 kasan_check_write+0x14/0x20 mm/kasan/kasan.c:278
 __atomic_add_unless include/asm-generic/atomic-instrumented.h:89 [inline]
 atomic_add_unless include/linux/atomic.h:533 [inline]
 mmget_not_zero include/linux/sched/mm.h:75 [inline]
 binder_update_page_range+0xece/0x18e0 drivers/android/binder_alloc.c:218
 binder_alloc_new_buf_locked drivers/android/binder_alloc.c:443 [inline]
 binder_alloc_new_buf+0x467/0xc30 drivers/android/binder_alloc.c:513
 binder_transaction+0x125b/0x4fb0 drivers/android/binder.c:2957
 binder_thread_write+0xc08/0x2770 drivers/android/binder.c:3528
 binder_ioctl_write_read.isra.39+0x24f/0x8e0 drivers/android/binder.c:4456
 binder_ioctl+0xa86/0xf34 drivers/android/binder.c:4596
 vfs_ioctl fs/ioctl.c:46 [inline]
 do_vfs_ioctl+0x154/0xd40 fs/ioctl.c:686
 ksys_ioctl+0x94/0xb0 fs/ioctl.c:701
 __do_sys_ioctl fs/ioctl.c:708 [inline]
 __se_sys_ioctl fs/ioctl.c:706 [inline]
 __x64_sys_ioctl+0x43/0x50 fs/ioctl.c:706
 do_syscall_64+0x167/0x4b0 arch/x86/entry/common.c:290
Signed-off-by: default avatarTodd Kjos <>
Signed-off-by: default avatarMinchan Kim <>
Reviewed-by: default avatarMartijn Coenen <>
Cc: stable <>
Signed-off-by: default avatarGreg Kroah-Hartman <>
Signed-off-by: default avatarGreg Kroah-Hartman <>
parent 381992bc
......@@ -324,6 +324,34 @@ static int binder_update_page_range(struct binder_alloc *alloc, int allocate,
return vma ? -ENOMEM : -ESRCH;
static inline void binder_alloc_set_vma(struct binder_alloc *alloc,
struct vm_area_struct *vma)
if (vma)
alloc->vma_vm_mm = vma->vm_mm;
* If we see alloc->vma is not NULL, buffer data structures set up
* completely. Look at smp_rmb side binder_alloc_get_vma.
* We also want to guarantee new alloc->vma_vm_mm is always visible
* if alloc->vma is set.
alloc->vma = vma;
static inline struct vm_area_struct *binder_alloc_get_vma(
struct binder_alloc *alloc)
struct vm_area_struct *vma = NULL;
if (alloc->vma) {
/* Look at description in binder_alloc_set_vma */
vma = alloc->vma;
return vma;
struct binder_buffer *binder_alloc_new_buf_locked(struct binder_alloc *alloc,
size_t data_size,
size_t offsets_size,
......@@ -339,7 +367,7 @@ struct binder_buffer *binder_alloc_new_buf_locked(struct binder_alloc *alloc,
size_t size, data_offsets_size;
int ret;
if (alloc->vma == NULL) {
if (!binder_alloc_get_vma(alloc)) {
pr_err("%d: binder_alloc_buf, no vma\n",
return ERR_PTR(-ESRCH);
......@@ -712,9 +740,7 @@ int binder_alloc_mmap_handler(struct binder_alloc *alloc,
buffer->free = 1;
binder_insert_free_buffer(alloc, buffer);
alloc->free_async_space = alloc->buffer_size / 2;
alloc->vma = vma;
alloc->vma_vm_mm = vma->vm_mm;
binder_alloc_set_vma(alloc, vma);
return 0;
......@@ -741,10 +767,10 @@ void binder_alloc_deferred_release(struct binder_alloc *alloc)
int buffers, page_count;
struct binder_buffer *buffer;
buffers = 0;
while ((n = rb_first(&alloc->allocated_buffers))) {
buffer = rb_entry(n, struct binder_buffer, rb_node);
......@@ -886,7 +912,7 @@ int binder_alloc_get_allocated_count(struct binder_alloc *alloc)
void binder_alloc_vma_close(struct binder_alloc *alloc)
WRITE_ONCE(alloc->vma, NULL);
binder_alloc_set_vma(alloc, NULL);
......@@ -921,7 +947,7 @@ enum lru_status binder_alloc_free_page(struct list_head *item,
index = page - alloc->pages;
page_addr = (uintptr_t)alloc->buffer + index * PAGE_SIZE;
vma = alloc->vma;
vma = binder_alloc_get_vma(alloc);
if (vma) {
if (!mmget_not_zero(alloc->vma_vm_mm))
goto err_mmget;
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