Re: [syzbot] [pvrusb2?] [usb?] KASAN: slab-use-after-free Read in pvr2_context_set_notify

Ricardo B. Marliere
2023-10-12T22:07:33Z

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#syz test: https://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb.git ce9ecca0238b140b88f43859b211c9fdfd8e5b70

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From cf7c3b08f80c4cdb7dd08cb977f29d41efebcf79 Mon Sep 17 00:00:00 2001
From: "Ricardo B. Marliere" <ricardo@marliere.net>
Date: Thu, 12 Oct 2023 18:26:47 -0300
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-by: syzbot+621409285c4156a009b3@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/all/000000000000a02a4205fff8eb92@google.com/
Signed-off-by: Ricardo B. Marliere <ricardo@marliere.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