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Date:   Mon,  7 Mar 2022 14:05:59 +0800
Message-Id: <20220307140437.Bluez.v1.1.Ieb7448d3d951876e1f412452fcfd27cdc7bd015b@changeid>
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Subject: [Bluez PATCH v1] audio: fix crash in a2dp_discover
From:   Howard Chung <howardchung@google.com>
To:     linux-bluetooth@vger.kernel.org, luiz.dentz@gmail.com
Cc:     chromeos-bluetooth-upstreaming@chromium.org,
        Yun-Hao Chung <howardchung@chromium.org>,
        Archie Pusaka <apusaka@chromium.org>
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From: Yun-Hao Chung <howardchung@chromium.org>

Sample stack trace:
0x0000567c394e4c6b (bluetoothd - a2dp.c: 270) setup_cb_free
0x0000567c394e4a94 (bluetoothd - a2dp.c: 2884) a2dp_discover
0x0000567c394e3c03 (bluetoothd - sink.c: 275) sink_setup_stream
0x0000567c394e3d4f (bluetoothd - sink.c: 299) sink_connect
0x0000567c39535183 (bluetoothd - service.c: 294) btd_service_connect
0x0000567c39539f68 (bluetoothd - device.c: 2006) connect_next
0x0000567c3954086d (bluetoothd - device.c: 2060) service_state_changed
0x0000567c39534efb (bluetoothd - service.c: 111) change_state
0x0000567c3953559c (bluetoothd - service.c: 0)
btd_service_connecting_complete
0x0000567c39534a5c (bluetoothd - profile.c: 1641) record_cb
0x0000567c395197cd (bluetoothd - sdp-client.c: 298) connect_watch
0x00007b14bc8034f6 (libglib-2.0.so.0 - gmain.c: 3337)
g_main_context_dispatch
0x00007b14bc803801 (libglib-2.0.so.0 - gmain.c: 4131)
g_main_context_iterate
0x00007b14bc803a7d (libglib-2.0.so.0 - gmain.c: 4329) g_main_loop_run
0x0000567c39566af1 (bluetoothd - mainloop-glib.c: 79) mainloop_run
0x0000567c39566ddb (bluetoothd - mainloop-notify.c: 201)
mainloop_run_with_signal
0x0000567c3954bf4c (bluetoothd - main.c: 1222) main
0x00007b14bc579797 (libc.so.6 - libc-start.c: 332) __libc_start_main
0x0000567c394df449 (bluetoothd) _start
0x00007ffd70145737

This could be triggered from a2dp_discover -> avdtp_discover ->
send_request -> send_req -> l2cap_connect (return error) ->
avdtp_set_state (to disconnect state)-> channel_remove -> channel_free
-> finalize_setup_errno (discover cb is freed) -> error handling all
the way back to a2dp_discover -> a2dp_discover (discover cb is freed
again, crashed!).

The fix is to add setup_ref/setup_unref around a2dp_discover to ensure
setup alive, and check if setup->chan to see if channel_free has been
called or not.

Reviewed-by: Archie Pusaka <apusaka@chromium.org>
---
Hi maintainers,

The fix is tested by forcing session->io to NULL in send_req in the code
and verifing the crash doesn't happen.

 profiles/audio/a2dp.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/profiles/audio/a2dp.c b/profiles/audio/a2dp.c
index 9fbcd35f7..39e1e9624 100644
--- a/profiles/audio/a2dp.c
+++ b/profiles/audio/a2dp.c
@@ -2878,14 +2878,22 @@ unsigned int a2dp_discover(struct avdtp *session, a2dp_discover_cb_t cb,
 	if (!setup)
 		return 0;
 
+	setup_ref(setup);
 	cb_data = setup_cb_new(setup);
 	cb_data->discover_cb = cb;
 	cb_data->user_data = user_data;
 
-	if (avdtp_discover(session, discover_cb, setup) == 0)
+	if (avdtp_discover(session, discover_cb, setup) == 0) {
+		setup_unref(setup);
 		return cb_data->id;
+	}
 
-	setup_cb_free(cb_data);
+	/* Check if the channel is still there before freeing setup_cb, since it
+	 * could be freed by channel_free().
+	 */
+	if (setup->chan)
+		setup_cb_free(cb_data);
+	setup_unref(setup);
 	return 0;
 }
 
-- 
2.35.1.616.g0bdcbb4464-goog