android: binder: fix the race mmap and alloc_new_buf_locked

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),
                                                      end_page_addr);

                                              // 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 qemu-project.org 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
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
"

Signed-off-by: Todd Kjos <tkjos@google.com>
Signed-off-by: Minchan Kim <minchan@kernel.org>
Reviewed-by: Martijn Coenen <maco@android.com>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/android/binder_alloc.c b/drivers/android/binder_alloc.c
index 3f3b7b2..64fd96e 100644 (file)
--- a/drivers/android/binder_alloc.c
+++ b/drivers/android/binder_alloc.c
@@ -332,6 +332,35 @@ err_no_vma:
        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.
+        */
+       smp_wmb();
+       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 */
+               smp_rmb();
+               vma = alloc->vma;
+       }
+       return vma;
+}
+
 static struct binder_buffer *binder_alloc_new_buf_locked(
                                struct binder_alloc *alloc,
                                size_t data_size,
@@ -348,7 +377,7 @@ static struct binder_buffer *binder_alloc_new_buf_locked(
        size_t size, data_offsets_size;
        int ret;
 
-       if (alloc->vma == NULL) {
+       if (!binder_alloc_get_vma(alloc)) {
                binder_alloc_debug(BINDER_DEBUG_USER_ERROR,
                                   "%d: binder_alloc_buf, no vma\n",
                                   alloc->pid);
@@ -723,9 +752,7 @@ 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;
-       barrier();
-       alloc->vma = vma;
-       alloc->vma_vm_mm = vma->vm_mm;
+       binder_alloc_set_vma(alloc, vma);
        mmgrab(alloc->vma_vm_mm);
 
        return 0;
@@ -754,10 +781,10 @@ void binder_alloc_deferred_release(struct binder_alloc *alloc)
        int buffers, page_count;
        struct binder_buffer *buffer;
 
-       BUG_ON(alloc->vma);
-
        buffers = 0;
        mutex_lock(&alloc->mutex);
+       BUG_ON(alloc->vma);
+
        while ((n = rb_first(&alloc->allocated_buffers))) {
                buffer = rb_entry(n, struct binder_buffer, rb_node);
 
@@ -900,7 +927,7 @@ 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);
 }
 
 /**
@@ -935,7 +962,7 @@ 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;