Messages in this thread | | | From | Todd Kjos <> | Date | Mon, 27 Jun 2022 08:43:47 -0700 | Subject | Re: [PATCH] android: binder: Fix lockdep check on clearing vma |
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On Mon, Jun 27, 2022 at 8:19 AM Liam Howlett <liam.howlett@oracle.com> wrote: > > 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. > > Reported-by: syzbot+da54fa8d793ca89c741f@syzkaller.appspotmail.com > Fixes: 472a68df605b ("android: binder: stop saving a pointer to the VMA") > Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Acked-by: Todd Kjos <tkjos@google.com> > --- > 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 f555eebceef6..1014beb12802 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; > } > > -- > 2.35.1
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