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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Todd Kjos <tkjos@google.com>,
        stable <stable@kernel.org>,
        Alessandro Astone <ales.astone@gmail.com>
Subject: [PATCH 5.17 032/225] binder: Gracefully handle BINDER_TYPE_FDA objects with num_fds=0
Date:   Wed,  4 May 2022 18:44:30 +0200
Message-Id: <20220504153113.119453489@linuxfoundation.org>
In-Reply-To: <20220504153110.096069935@linuxfoundation.org>
References: <20220504153110.096069935@linuxfoundation.org>
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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>
---
 drivers/android/binder.c |    3 +++
 1 file changed, 3 insertions(+)

--- a/drivers/android/binder.c
+++ b/drivers/android/binder.c
@@ -2486,6 +2486,9 @@ static int binder_translate_fd_array(str
 	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",