From: Liam Howlett <liam.howlett@xxxxxxxxxx> 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@xxxxxxxxxx Fixes: 472a68df605b ("android: binder: stop saving a pointer to the VMA") Signed-off-by: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx> Reported-by: syzbot+da54fa8d793ca89c741f@xxxxxxxxxxxxxxxxxxxxxxxxx Acked-by: Todd Kjos <tkjos@xxxxxxxxxx> Cc: "Arve Hjønnevåg" <arve@xxxxxxxxxxx> Cc: Christian Brauner (Microsoft) <brauner@xxxxxxxxxx> Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> Cc: Hridya Valsaraju <hridya@xxxxxxxxxx> Cc: Joel Fernandes <joel@xxxxxxxxxxxxxxxxx> Cc: Martijn Coenen <maco@xxxxxxxxxxx> Cc: Suren Baghdasaryan <surenb@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- 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; }
