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Date:   Wed, 30 Nov 2022 03:58:05 +0000
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Subject: [PATCH 5.10 6/6] binder: Gracefully handle BINDER_TYPE_FDA objects
 with num_fds=0
From:   Carlos Llamas <cmllamas@google.com>
To:     stable@kernel.org, Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "=?UTF-8?q?Arve=20Hj=C3=B8nnev=C3=A5g?=" <arve@android.com>,
        Todd Kjos <tkjos@android.com>,
        Martijn Coenen <maco@android.com>,
        Joel Fernandes <joel@joelfernandes.org>,
        Christian Brauner <christian@brauner.io>,
        Hridya Valsaraju <hridya@google.com>,
        Suren Baghdasaryan <surenb@google.com>
Cc:     linux-kernel@vger.kernel.org, kernel-team@android.com,
        Alessandro Astone <ales.astone@gmail.com>,
        Todd Kjos <tkjos@google.com>,
        Carlos Llamas <cmllamas@google.com>
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From: Alessandro Astone <ales.astone@gmail.com>

commit ef38de9217a04c9077629a24652689d8fdb4c6c6 upstream.

Some android userspace is sending BINDER_TYPE_FDA objects with
num_fds=0. Like the previous patch, this is reproducible when
playing a video.

Before commit 09184ae9b575 BINDER_TYPE_FDA objects with num_fds=0
were 'correctly handled', as in no fixup was performed.

After commit 09184ae9b575 we aggregate fixup and skip regions in
binder_ptr_fixup structs and distinguish between the two by using
the skip_size field: if it's 0, then it's a fixup, otherwise skip.
When processing BINDER_TYPE_FDA objects with num_fds=0 we add a
skip region of skip_size=0, and this causes issues because now
binder_do_deferred_txn_copies will think this was a fixup region.

To address that, return early from binder_translate_fd_array to
avoid adding an empty skip region.

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/20220415120015.52684-1-ales.astone@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Carlos Llamas <cmllamas@google.com>
---
 drivers/android/binder.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/android/binder.c b/drivers/android/binder.c
index 1ba8a98094b4..4473adef2f5a 100644
--- a/drivers/android/binder.c
+++ b/drivers/android/binder.c
@@ -2891,6 +2891,9 @@ static int binder_translate_fd_array(struct list_head *pf_head,
 	struct binder_proc *proc = thread->proc;
 	int ret;
 
+	if (fda->num_fds == 0)
+		return 0;
+
 	fd_buf_size = sizeof(u32) * fda->num_fds;
 	if (fda->num_fds >= SIZE_MAX / sizeof(u32)) {
 		binder_user_error("%d:%d got transaction with invalid number of fds (%lld)\n",
-- 
2.38.1.584.g0f3c55d4c2-goog