Patch "usb: dwc2: fix possible NULL pointer dereference caused by driver concurrency" has been added to the 5.4-stable tree

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This is a note to let you know that I've just added the patch titled

    usb: dwc2: fix possible NULL pointer dereference caused by driver concurrency

to the 5.4-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     usb-dwc2-fix-possible-null-pointer-dereference-cause.patch
and it can be found in the queue-5.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 3c27f6cdb62a27859a77a7b93c1de7c20ecc7415
Author: Jia-Ju Bai <baijiaju@xxxxxxxxxxx>
Date:   Tue Sep 26 10:44:04 2023 +0800

    usb: dwc2: fix possible NULL pointer dereference caused by driver concurrency
    
    [ Upstream commit ef307bc6ef04e8c1ea843231db58e3afaafa9fa6 ]
    
    In _dwc2_hcd_urb_enqueue(), "urb->hcpriv = NULL" is executed without
    holding the lock "hsotg->lock". In _dwc2_hcd_urb_dequeue():
    
        spin_lock_irqsave(&hsotg->lock, flags);
        ...
            if (!urb->hcpriv) {
                    dev_dbg(hsotg->dev, "## urb->hcpriv is NULL ##\n");
                    goto out;
            }
        rc = dwc2_hcd_urb_dequeue(hsotg, urb->hcpriv); // Use urb->hcpriv
        ...
    out:
        spin_unlock_irqrestore(&hsotg->lock, flags);
    
    When _dwc2_hcd_urb_enqueue() and _dwc2_hcd_urb_dequeue() are
    concurrently executed, the NULL check of "urb->hcpriv" can be executed
    before "urb->hcpriv = NULL". After urb->hcpriv is NULL, it can be used
    in the function call to dwc2_hcd_urb_dequeue(), which can cause a NULL
    pointer dereference.
    
    This possible bug is found by an experimental static analysis tool
    developed by myself. This tool analyzes the locking APIs to extract
    function pairs that can be concurrently executed, and then analyzes the
    instructions in the paired functions to identify possible concurrency
    bugs including data races and atomicity violations. The above possible
    bug is reported, when my tool analyzes the source code of Linux 6.5.
    
    To fix this possible bug, "urb->hcpriv = NULL" should be executed with
    holding the lock "hsotg->lock". After using this patch, my tool never
    reports the possible bug, with the kernelconfiguration allyesconfig for
    x86_64. Because I have no associated hardware, I cannot test the patch
    in runtime testing, and just verify it according to the code logic.
    
    Fixes: 33ad261aa62b ("usb: dwc2: host: spinlock urb_enqueue")
    Signed-off-by: Jia-Ju Bai <baijiaju@xxxxxxxxxxx>
    Link: https://lore.kernel.org/r/20230926024404.832096-1-baijiaju@xxxxxxxxxxx
    Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/drivers/usb/dwc2/hcd.c b/drivers/usb/dwc2/hcd.c
index a412ef67af18d..7b8dee3087f35 100644
--- a/drivers/usb/dwc2/hcd.c
+++ b/drivers/usb/dwc2/hcd.c
@@ -4684,8 +4684,8 @@ static int _dwc2_hcd_urb_enqueue(struct usb_hcd *hcd, struct urb *urb,
 	if (qh_allocated && qh->channel && qh->channel->qh == qh)
 		qh->channel->qh = NULL;
 fail2:
-	spin_unlock_irqrestore(&hsotg->lock, flags);
 	urb->hcpriv = NULL;
+	spin_unlock_irqrestore(&hsotg->lock, flags);
 	kfree(qtd);
 fail1:
 	if (qh_allocated) {



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