staging: android: ashmem: Fix mmap size validation

The ashmem driver did not check that the size/offset of the vma passed
to its .mmap() function was not larger than the ashmem object being
mapped. This could cause mmap() to succeed, even though accessing parts
of the mapping would later fail with a segmentation fault.

Ensure an error is returned by the ashmem_mmap() function if the vma
size is larger than the ashmem object size. This enables safer handling
of the problem in userspace.

Cc: Todd Kjos <tkjos@android.com>
Cc: devel@driverdev.osuosl.org
Cc: linux-kernel@vger.kernel.org
Cc: kernel-team@android.com
Cc: Joel Fernandes <joel@joelfernandes.org>
Signed-off-by: Alistair Strachan <astrachan@google.com>
Acked-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Reviewed-by: Martijn Coenen <maco@android.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/staging/android/ashmem.c b/drivers/staging/android/ashmem.c
index c6386e4f5c9bc103af87aa53e0b1f42513b5b4a7..e392358ec244c18dca6e041d0ea3c89863aab90b 100644 (file)
--- a/drivers/staging/android/ashmem.c
+++ b/drivers/staging/android/ashmem.c
@@ -366,6 +366,12 @@ static int ashmem_mmap(struct file *file, struct vm_area_struct *vma)
                goto out;
        }
 
+       /* requested mapping size larger than object size */
+       if (vma->vm_end - vma->vm_start > PAGE_ALIGN(asma->size)) {
+               ret = -EINVAL;
+               goto out;
+       }
+
        /* requested protection bits must match our allowed protection mask */
        if ((vma->vm_flags & ~calc_vm_prot_bits(asma->prot_mask, 0)) &
            calc_vm_prot_bits(PROT_MASK, 0)) {