linux-kernel - [PATCH] media: pvrusb2: fix use after free on context disconnection

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Message-ID: <20231012230911.48113-2-ricardo@marliere.net>
Date:   Thu, 12 Oct 2023 20:09:12 -0300
From:   "Ricardo B. Marliere" <ricardo@...liere.net>
To:     Mike Isely <isely@...ox.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>
Cc:     linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-kernel-mentees@...ts.linuxfoundation.org,
        "Ricardo B. Marliere" <ricardo@...liere.net>,
        syzbot+621409285c4156a009b3@...kaller.appspotmail.com
Subject: [PATCH] media: pvrusb2: fix use after free on context disconnection

Upon module load, a kthread is created targeting the
pvr2_context_thread_func function, which may call pvr2_context_destroy
and thus call kfree() on the context object. However, that might happen
before the usb hub_event handler is able to notify the driver. This
patch adds a sanity check before the invalid read reported by syzbot,
within the context disconnection call stack.

Fixes: e5be15c63804 ("V4L/DVB (7711): pvrusb2: Fix race on module unload")
Reported-and-tested-by: syzbot+621409285c4156a009b3@...kaller.appspotmail.com
Closes: https://lore.kernel.org/all/000000000000a02a4205fff8eb92@google.com/
Signed-off-by: Ricardo B. Marliere <ricardo@...liere.net>
---
 drivers/media/usb/pvrusb2/pvrusb2-context.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/media/usb/pvrusb2/pvrusb2-context.c b/drivers/media/usb/pvrusb2/pvrusb2-context.c
index 14170a5d72b3..1764674de98b 100644
--- a/drivers/media/usb/pvrusb2/pvrusb2-context.c
+++ b/drivers/media/usb/pvrusb2/pvrusb2-context.c
@@ -268,7 +268,8 @@ void pvr2_context_disconnect(struct pvr2_context *mp)
 {
 	pvr2_hdw_disconnect(mp->hdw);
 	mp->disconnect_flag = !0;
-	pvr2_context_notify(mp);
+	if (!pvr2_context_shutok())
+		pvr2_context_notify(mp);
 }
 
 
-- 
2.42.0