tree 566dfed8416fa25f55be10b5abc9213c6acf7fd8
parent 03d4af8271682742aa21bbbf3032a839764f591a
author Todd Kjos <tkjos@google.com> 1510356627 -0800
committer Todd Kjos <tkjos@google.com> 1510777102 -0800

FROMLIST: binder: fix proc->files use-after-free

(from https://patchwork.kernel.org/patch/10058587/)

proc->files cleanup is initiated by binder_vma_close. Therefore
a reference on the binder_proc is not enough to prevent the
files_struct from being released while the binder_proc still has
a reference. This can lead to an attempt to dereference the
stale pointer obtained from proc->files prior to proc->files
cleanup. This has been seen once in task_get_unused_fd_flags()
when __alloc_fd() is called with a stale "files".

The fix is to always use get_files_struct() to obtain struct_files
so that the refcount on the files_struct is used to prevent
a premature free. proc->files is removed since we get it every
time.

Bug: 69164715
Change-Id: I6431027d3d569e76913935c21885201505627982
Signed-off-by: Todd Kjos <tkjos@google.com>