linux-kernel - Re: [BUG]: slab-use-after-free Read in mgmt_set_powered

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Message-ID: <CABBYNZ+xg05sbfU51VXo1M=PqPOktDtRpTe5yHwwUhF9ui+NPA@mail.gmail.com>
Date: Fri, 12 Sep 2025 14:29:34 -0400
From: Luiz Augusto von Dentz <luiz.dentz@...il.com>
To: cen zhang <zzzccc427@...il.com>
Cc: johan.hedberg@...il.com, marcel@...tmann.org, linux-kernel@...r.kernel.org, 
	baijiaju1990@...il.com, zhenghaoran154@...il.com, r33s3n6@...il.com, 
	linux-bluetooth@...r.kernel.org, "gality369@...il.com" <gality369@...il.com>
Subject: Re: [BUG]: slab-use-after-free Read in mgmt_set_powered_complete

Hi Cen,

On Fri, Sep 12, 2025 at 11:59 AM cen zhang <zzzccc427@...il.com> wrote:
>
> Hi Luiz,
>
> Thank you for your quick response and the important clarification
> about hci_cmd_sync_dequeue().
>
> You are absolutely correct - I was indeed referring to the TOCTOU
> problem in pending_find(), not the -ECANCELED check. The
> hci_cmd_sync_dequeue() call in cmd_complete_rsp() is a crucial detail
> that I initially overlooked in my analysis.
>
> After examining the code more carefully, I can see that while
> hci_cmd_sync_dequeue() does attempt to remove pending sync commands
> from the queue, but it cannot prevent the race condition we're seeing.
> The fundamental issue is that hci_cmd_sync_dequeue() can only remove
> work items that are still queued, but cannot stop work items that are
> already executing or about to execute their completion callbacks.
>
> The race window occurs when:
> 1. mgmt_set_powered_complete() is about to execute (work item has been dequeued)
> 2. mgmt_index_removed() -> mgmt_pending_foreach() -> cmd_complete_rsp() executes
> 3. hci_cmd_sync_dequeue() removes queued items but cannot affect the
> already-running callback
> 4. mgmt_pending_free() frees the cmd object
> 5. mgmt_set_powered_complete() still executes and accesses freed cmd->param
>
> I am sorry that I haven't get a reliable reproducer from syzkaller for
> this bug may be due to it is timing-sensitive.

Let's try to fix all instances then, since apparently there is more
than one cmd with this pattern, please test with the attached patch.

View attachment "v4-0003-Bluetooth-MGMT-Fix-possible-UAFs.patch" of type "text/x-patch" (19489 bytes)