binder: Gracefully handle BINDER_TYPE_FDA objects with num_fds=0

stable inclusion
from stable-v5.10.157
commit ae9e0cc973fb7499ea1b1a8dfd0795f728b84faf
category: bugfix
bugzilla: https://gitee.com/src-openeuler/kernel/issues/I6DKVG
CVE: CVE-2023-20938

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ae9e0cc973fb7499ea1b1a8dfd0795f728b84faf

--------------------------------

commit ef38de92 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 09184ae9 BINDER_TYPE_FDA objects with num_fds=0
were 'correctly handled', as in no fixup was performed.

After commit 09184ae9 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: 09184ae9 ("binder: defer copies of pre-patched txn data")
Acked-by: NTodd Kjos <tkjos@google.com>
Cc: stable <stable@kernel.org>
Signed-off-by: NAlessandro Astone <ales.astone@gmail.com>
Link: https://lore.kernel.org/r/20220415120015.52684-1-ales.astone@gmail.comSigned-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: NCarlos Llamas <cmllamas@google.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: NLi Huafei <lihuafei1@huawei.com>
Reviewed-by: NZheng Yejian <zhengyejian1@huawei.com>
Reviewed-by: NXiu Jianfeng <xiujianfeng@huawei.com>
Signed-off-by: NJialin Zhang <zhangjialin11@huawei.com>

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",