From d25d6744c46b8289d61180bafb30f3140fef24a4 Mon Sep 17 00:00:00 2001 From: Liam Howlett Date: Mon, 27 Jun 2022 15:18:59 +0000 Subject: [PATCH] android: binder: fix lockdep check on clearing vma MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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 Reported-by: syzbot+da54fa8d793ca89c741f@syzkaller.appspotmail.com Acked-by: Todd Kjos Cc: "Arve Hjønnevåg" Cc: Christian Brauner (Microsoft) Cc: Greg Kroah-Hartman Cc: Hridya Valsaraju Cc: Joel Fernandes Cc: Martijn Coenen Cc: Suren Baghdasaryan Signed-off-by: Andrew Morton Signed-off-by: Greg Kroah-Hartman --- drivers/android/binder_alloc.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/drivers/android/binder_alloc.c b/drivers/android/binder_alloc.c index 7981a2598376..5d437c0c842c 100644 --- a/drivers/android/binder_alloc.c +++ b/drivers/android/binder_alloc.c @@ -315,12 +315,19 @@ static inline void binder_alloc_set_vma(struct binder_alloc *alloc, { 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; }