binder: Address corner cases in deferred copy and fixup

When handling BINDER_TYPE_FDA object we are pushing a parent fixup
with a certain skip_size but no scatter-gather copy object, since
the copy is handled standalone.
If BINDER_TYPE_FDA is the last children the scatter-gather copy
loop will never stop to skip it, thus we are left with an item in
the parent fixup list. This will trigger the BUG_ON().

This is reproducible in android when playing a video.
We receive a transaction that looks like this:
    obj[0] BINDER_TYPE_PTR, parent
    obj[1] BINDER_TYPE_PTR, child
    obj[2] BINDER_TYPE_PTR, child
    obj[3] BINDER_TYPE_FDA, child

Fixes: 09184ae9b575 ("binder: defer copies of pre-patched txn data")
Acked-by: Todd Kjos <tkjos@google.com>
Cc: stable <stable@kernel.org>
Signed-off-by: Alessandro Astone <ales.astone@gmail.com>
Link: https://lore.kernel.org/r/20220415120015.52684-2-ales.astone@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/android/binder.c b/drivers/android/binder.c
index 8351c56..31176ed 100644 (file)
--- a/drivers/android/binder.c
+++ b/drivers/android/binder.c
@@ -2295,6 +2295,7 @@ static int binder_do_deferred_txn_copies(struct binder_alloc *alloc,
 {
        int ret = 0;
        struct binder_sg_copy *sgc, *tmpsgc;
+       struct binder_ptr_fixup *tmppf;
        struct binder_ptr_fixup *pf =
                list_first_entry_or_null(pf_head, struct binder_ptr_fixup,
                                         node);
@@ -2349,7 +2350,11 @@ static int binder_do_deferred_txn_copies(struct binder_alloc *alloc,
                list_del(&sgc->node);
                kfree(sgc);
        }
-       BUG_ON(!list_empty(pf_head));
+       list_for_each_entry_safe(pf, tmppf, pf_head, node) {
+               BUG_ON(pf->skip_size == 0);
+               list_del(&pf->node);
+               kfree(pf);
+       }
        BUG_ON(!list_empty(sgc_head));
 
        return ret > 0 ? -EINVAL : ret;