Staging: android: binder: Fix crashes when sharing a binder file between processes

Opening the binder driver and sharing the file returned with
other processes (e.g. by calling fork) can crash the kernel.
Prevent these crashes with the following changes:
- Add a mutex to protect against two processes mmapping the
  same binder_proc.
- After locking mmap_sem, check that the vma we want to access
  (still) points to the same mm_struct.
- Use proc->tsk instead of current to get the files struct since
  this is where we get the rlimit from.

Signed-off-by: Arve Hjønnevåg <arve@android.com>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/staging/android/binder.c b/drivers/staging/android/binder.c
index 48cf27cdb51a1f907a18f5d03d6c44285432ff9e..f0b7e6605ab5e4969d88a2112498439362454f82 100644 (file)
--- a/drivers/staging/android/binder.c
+++ b/drivers/staging/android/binder.c
@@ -38,6 +38,7 @@
 
 static DEFINE_MUTEX(binder_lock);
 static DEFINE_MUTEX(binder_deferred_lock);
+static DEFINE_MUTEX(binder_mmap_lock);
 
 static HLIST_HEAD(binder_procs);
 static HLIST_HEAD(binder_deferred_list);
@@ -632,6 +633,11 @@ static int binder_update_page_range(struct binder_proc *proc, int allocate,
        if (mm) {
                down_write(&mm->mmap_sem);
                vma = proc->vma;
+               if (vma && mm != vma->vm_mm) {
+                       pr_err("binder: %d: vma mm and task mm mismatch\n",
+                               proc->pid);
+                       vma = NULL;
+               }
        }
 
        if (allocate == 0)
@@ -2802,6 +2808,7 @@ static int binder_mmap(struct file *filp, struct vm_area_struct *vma)
        }
        vma->vm_flags = (vma->vm_flags | VM_DONTCOPY) & ~VM_MAYWRITE;
 
+       mutex_lock(&binder_mmap_lock);
        if (proc->buffer) {
                ret = -EBUSY;
                failure_string = "already mapped";
@@ -2816,6 +2823,7 @@ static int binder_mmap(struct file *filp, struct vm_area_struct *vma)
        }
        proc->buffer = area->addr;
        proc->user_buffer_offset = vma->vm_start - (uintptr_t)proc->buffer;
+       mutex_unlock(&binder_mmap_lock);
 
 #ifdef CONFIG_CPU_CACHE_VIPT
        if (cache_is_vipt_aliasing()) {
@@ -2848,7 +2856,7 @@ static int binder_mmap(struct file *filp, struct vm_area_struct *vma)
        binder_insert_free_buffer(proc, buffer);
        proc->free_async_space = proc->buffer_size / 2;
        barrier();
-       proc->files = get_files_struct(current);
+       proc->files = get_files_struct(proc->tsk);
        proc->vma = vma;
 
        /*printk(KERN_INFO "binder_mmap: %d %lx-%lx maps %p\n",
@@ -2859,10 +2867,12 @@ err_alloc_small_buf_failed:
        kfree(proc->pages);
        proc->pages = NULL;
 err_alloc_pages_failed:
+       mutex_lock(&binder_mmap_lock);
        vfree(proc->buffer);
        proc->buffer = NULL;
 err_get_vm_area_failed:
 err_already_mapped:
+       mutex_unlock(&binder_mmap_lock);
 err_bad_arg:
        printk(KERN_ERR "binder_mmap: %d %lx-%lx %s failed %d\n",
               proc->pid, vma->vm_start, vma->vm_end, failure_string, ret);