• Liam R. Howlett's avatar
    android: binder: stop saving a pointer to the VMA · a43cfc87
    Liam R. Howlett authored
    Do not record a pointer to a VMA outside of the mmap_lock for later use. 
    This is unsafe and there are a number of failure paths *after* the
    recorded VMA pointer may be freed during setup.  There is no callback to
    the driver to clear the saved pointer from generic mm code.  Furthermore,
    the VMA pointer may become stale if any number of VMA operations end up
    freeing the VMA so saving it was fragile to being with.
    
    Instead, change the binder_alloc struct to record the start address of the
    VMA and use vma_lookup() to get the vma when needed.  Add lockdep
    mmap_lock checks on updates to the vma pointer to ensure the lock is held
    and depend on that lock for synchronization of readers and writers - which
    was already the case anyways, so the smp_wmb()/smp_rmb() was not
    necessary.
    
    [akpm@linux-foundation.org: fix drivers/android/binder_alloc_selftest.c]
    Link: https://lkml.kernel.org/r/20220621140212.vpkio64idahetbyf@revolver
    Fixes: da1b9564 ("android: binder: fix the race mmap and alloc_new_buf_locked")
    Reported-by: syzbot+58b51ac2b04e388ab7b0@syzkaller.appspotmail.com
    Signed-off-by: default avatarLiam R. Howlett <Liam.Howlett@oracle.com>
    Cc: Minchan Kim <minchan@kernel.org>
    Cc: Christian Brauner (Microsoft) <brauner@kernel.org>
    Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    Cc: Hridya Valsaraju <hridya@google.com>
    Cc: Joel Fernandes <joel@joelfernandes.org>
    Cc: Martijn Coenen <maco@android.com>
    Cc: Suren Baghdasaryan <surenb@google.com>
    Cc: Todd Kjos <tkjos@android.com>
    Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    a43cfc87
binder_alloc.h 6.43 KB