Jann Horn
015c08bc70
commita7a74d7ff5upstream. binder_alloc_mmap_handler() attempts to detect the use of ->mmap() on a binder_proc whose binder_alloc has already been initialized by checking whether alloc->buffer is non-zero. Before commit880211667b("binder: remove kernel vm_area for buffer space"), alloc->buffer was a kernel mapping address, which is always non-zero, but since that commit, it is a userspace mapping address. A sufficiently privileged user can map /dev/binder at NULL, tricking binder_alloc_mmap_handler() into assuming that the binder_proc has not been mapped yet. This leads to memory unsafety. Luckily, no context on Android has such privileges, and on a typical Linux desktop system, you need to be root to do that. Fix it by using the mapping size instead of the mapping address to distinguish the mapped case. A valid VMA can't have size zero. Fixes:880211667b("binder: remove kernel vm_area for buffer space") Cc: stable@vger.kernel.org Signed-off-by: Jann Horn <jannh@google.com> Acked-by: Christian Brauner <christian.brauner@ubuntu.com> Link: https://lore.kernel.org/r/20191018205631.248274-2-jannh@google.com Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.