From: Liam Howlett liam.howlett@oracle.com
commit b0cab80ecd54ae3b2356bb081af0bffd538c8265 upstream.
When munmapping a vma, the mmap_lock can be degraded to a write before calling close() on the file handle. The binder close() function calls binder_alloc_set_vma() to clear the vma address, which now has a lock dep check for writing on the mmap_lock. Change the lockdep check to ensure the reading lock is held while clearing and keep the write check while writing.
Link: https://lkml.kernel.org/r/20220627151857.2316964-1-Liam.Howlett@oracle.com Fixes: 472a68df605b ("android: binder: stop saving a pointer to the VMA") Signed-off-by: Liam R. Howlett Liam.Howlett@oracle.com Reported-by: syzbot+da54fa8d793ca89c741f@syzkaller.appspotmail.com Acked-by: Todd Kjos tkjos@google.com Cc: "Arve Hjønnevåg" arve@android.com 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 Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/android/binder_alloc.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-)
--- a/drivers/android/binder_alloc.c +++ b/drivers/android/binder_alloc.c @@ -315,12 +315,19 @@ static inline void binder_alloc_set_vma( { unsigned long vm_start = 0;
+ /* + * Allow clearing the vma with holding just the read lock to allow + * munmapping downgrade of the write lock before freeing and closing the + * file using binder_alloc_vma_close(). + */ if (vma) { vm_start = vma->vm_start; alloc->vma_vm_mm = vma->vm_mm; + mmap_assert_write_locked(alloc->vma_vm_mm); + } else { + mmap_assert_locked(alloc->vma_vm_mm); }
- mmap_assert_write_locked(alloc->vma_vm_mm); alloc->vma_addr = vm_start; }