From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B26353D9033; Wed, 8 Apr 2026 19:02:15 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775674935; cv=none; b=iXWjueoyONKIanv9XP5K/AoiX5U24GSpo5mob4fFXPlwNrHip6yzte7GNUrsA2Ag5t/XiaLNb+2O2pYCdRKNNYX/xvklVdiu8PvE6ResnO7+fD8LWGo59MuCLLNa5Zs1acU2/PdsYqYJcSxpI2h7iGLd5nqGdba6W/4gCKSFGWM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775674935; c=relaxed/simple; bh=YdIP1mYocCPOlllMmLfdf3zHqP0fLhyy8vRQyxvmGb0=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=R6UgiVWayarPHkYyxDqpEXVa66P1EC4zeHyhL69DeZQ6JaRumsJM29XNnInWS4V9/JCK3/fM/YUpd3j8QFxt5YiR23FHCrcJimfljedwHzL9tpgfT1fLX2OMWKlrK0dkdGXdiKauEXtrSqM5TVpBPbEDES2BI8oyszSGNWfTS10= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=lMfl7Uay; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="lMfl7Uay" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4699EC2BC9E; Wed, 8 Apr 2026 19:02:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1775674935; bh=YdIP1mYocCPOlllMmLfdf3zHqP0fLhyy8vRQyxvmGb0=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=lMfl7UayQYqGwaSoIqn/MNwLg9hITPoot7WZeWV2o402XzypE3fMH0XkYjLZi7PKC sb3LtVNttlpk4LaJXucKlW1k74LguI2jDwuausKKyto7UYpFNpo3aQ2OQhxsyEIONm I+qRDeQouxNkqI6GFEpPmnlx7VucUW2bFCfC+Pxo= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Alan Stern , syzbot+19bed92c97bee999e5db@syzkaller.appspotmail.com, stable Subject: [PATCH 6.19 291/311] USB: dummy-hcd: Fix locking/synchronization error Date: Wed, 8 Apr 2026 20:04:51 +0200 Message-ID: <20260408175950.245335328@linuxfoundation.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260408175939.393281918@linuxfoundation.org> References: <20260408175939.393281918@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.19-stable review patch. If anyone has any objections, please let me know. ------------------ From: Alan Stern commit 616a63ff495df12863692ab3f9f7b84e3fa7a66d upstream. Syzbot testing was able to provoke an addressing exception and crash in the usb_gadget_udc_reset() routine in drivers/usb/gadgets/udc/core.c, resulting from the fact that the routine was called with a second ("driver") argument of NULL. The bad caller was set_link_state() in dummy_hcd.c, and the problem arose because of a race between a USB reset and driver unbind. These sorts of races were not supposed to be possible; commit 7dbd8f4cabd9 ("USB: dummy-hcd: Fix erroneous synchronization change"), along with a few followup commits, was written specifically to prevent them. As it turns out, there are (at least) two errors remaining in the code. Another patch will address the second error; this one is concerned with the first. The error responsible for the syzbot crash occurred because the stop_activity() routine will sometimes drop and then re-acquire the dum->lock spinlock. A call to stop_activity() occurs in set_link_state() when handling an emulated USB reset, after the test of dum->ints_enabled and before the increment of dum->callback_usage. This allowed another thread (doing a driver unbind) to sneak in and grab the spinlock, and then clear dum->ints_enabled and dum->driver. Normally this other thread would have to wait for dum->callback_usage to go down to 0 before it would clear dum->driver, but in this case it didn't have to wait since dum->callback_usage had not yet been incremented. The fix is to increment dum->callback_usage _before_ calling stop_activity() instead of after. Then the thread doing the unbind will not clear dum->driver until after the call to usb_gadget_udc_reset() safely returns and dum->callback_usage has been decremented again. Signed-off-by: Alan Stern Reported-by: syzbot+19bed92c97bee999e5db@syzkaller.appspotmail.com Closes: https://lore.kernel.org/linux-usb/68fc7c9c.050a0220.346f24.023c.GAE@google.com/ Tested-by: syzbot+19bed92c97bee999e5db@syzkaller.appspotmail.com Fixes: 7dbd8f4cabd9 ("USB: dummy-hcd: Fix erroneous synchronization change") Cc: stable Link: https://patch.msgid.link/46135f42-fdbe-46b5-aac0-6ca70492af15@rowland.harvard.edu Signed-off-by: Greg Kroah-Hartman --- drivers/usb/gadget/udc/dummy_hcd.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) --- a/drivers/usb/gadget/udc/dummy_hcd.c +++ b/drivers/usb/gadget/udc/dummy_hcd.c @@ -462,8 +462,13 @@ static void set_link_state(struct dummy_ /* Report reset and disconnect events to the driver */ if (dum->ints_enabled && (disconnect || reset)) { - stop_activity(dum); ++dum->callback_usage; + /* + * stop_activity() can drop dum->lock, so it must + * not come between the dum->ints_enabled test + * and the ++dum->callback_usage. + */ + stop_activity(dum); spin_unlock(&dum->lock); if (reset) usb_gadget_udc_reset(&dum->gadget, dum->driver);