Re: [syzbot] [pvrusb2?] [usb?] KASAN: slab-use-after-free Read in pvr2_context_set_notify (3)

[Hillf Danton]

On Sat, 13 Apr 2024 21:26:30 -0700
> syzbot found the following issue on:
> 
> HEAD commit:    a788e53c05ae usb: usb-acpi: Fix oops due to freeing uninit..
> git tree:       https://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb.git usb-testing
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=120ca915180000

#syz test https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git  master

--- x/drivers/media/usb/pvrusb2/pvrusb2-context.c
+++ y/drivers/media/usb/pvrusb2/pvrusb2-context.c
@@ -26,6 +26,8 @@ static int pvr2_context_cleanup_flag;
 static int pvr2_context_cleaned_flag;
 static struct task_struct *pvr2_context_thread_ptr;
 
+static DEFINE_MUTEX(pvr2_disconn_mutex);
+static int pvr2_context_cleaning;
 
 static void pvr2_context_set_notify(struct pvr2_context *mp, int fl)
 {
@@ -152,6 +154,9 @@ static int pvr2_context_thread_func(void
 
 	pvr2_trace(PVR2_TRACE_CTXT,"pvr2_context thread start");
 
+	mutex_lock(&pvr2_disconn_mutex);
+	pvr2_context_cleaning = 1;
+	mutex_unlock(&pvr2_disconn_mutex);
 	do {
 		while ((mp = pvr2_context_notify_first) != NULL) {
 			pvr2_context_set_notify(mp, 0);
@@ -163,6 +168,9 @@ static int pvr2_context_thread_func(void
 			 pvr2_context_shutok()));
 	} while (!pvr2_context_shutok());
 
+	mutex_lock(&pvr2_disconn_mutex);
+	pvr2_context_cleaning = 0;
+	mutex_unlock(&pvr2_disconn_mutex);
 	pvr2_context_cleaned_flag = !0;
 	wake_up(&pvr2_context_cleanup_data);
 
@@ -266,13 +274,17 @@ static void pvr2_context_exit(struct pvr
 
 void pvr2_context_disconnect(struct pvr2_context *mp)
 {
+	mutex_lock(&pvr2_disconn_mutex);
+	if (pvr2_context_cleaning)
+		goto out;
 	pvr2_hdw_disconnect(mp->hdw);
 	if (!pvr2_context_shutok())
 		pvr2_context_notify(mp);
 	mp->disconnect_flag = !0;
+out:
+	mutex_unlock(&pvr2_disconn_mutex);
 }
 
-
 void pvr2_channel_init(struct pvr2_channel *cp,struct pvr2_context *mp)
 {
 	pvr2_context_enter(mp);
--