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 963C6423A8A; Tue, 31 Mar 2026 16:57:00 +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=1774976220; cv=none; b=TAji5bm1CkHH421zMw16FKorXETk08XETecuB9n/G4hK7N7sSgsQ30vmNTvi2IWvt7B3/7HM1AIct4/9dyDwDAHIlCWKPJJjcRDpO/q3xl5awpJP8rQgr+w5NSuI9+vL9nZMjGj5i8zW1cD21ayUJo28jFWIUtQ7XDJDDxq6hh8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774976220; c=relaxed/simple; bh=jKBFJ6YgYJgVyfYCDIz9MrNviwgdjBH2zFerTNVx1aI=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=q1BNInyynpoAya/XcvT3Tdubb+e4oeTZxLSHvVBzSCH+X2L6NWoof0G+B51LzjbyTDS99IN4GZlp1ndfCrjf2sMFIUjyOhKH1BgjIiCXJnZSoymelxV1YXFPmEyhg2YJN1NvCDEopID2VC0Yi0ITZSiuP6vPo2EkQP5fhxcEwO4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=VL4djyAZ; 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="VL4djyAZ" Received: by smtp.kernel.org (Postfix) with ESMTPSA id CBA0FC19423; Tue, 31 Mar 2026 16:56:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1774976220; bh=jKBFJ6YgYJgVyfYCDIz9MrNviwgdjBH2zFerTNVx1aI=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=VL4djyAZzzLRLrIy48PqKrghDuZoBP9+zR0bn9LIXbVfvSJOPOHKjZfsG1giWsduf zDwQSg6jqkYRm0NkZimt8i3QCQX32v1pQj5QZnjgVgS4Ch/yUkJwpiVHK5we/dbQQB 0zOu/tHGoxdEuJgNrGkm9jm/DxQeGS6tKaxrmQIw= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Dave Jiang , Li Ming , Alison Schofield , Jonathan Cameron , Sasha Levin Subject: [PATCH 6.18 001/309] cxl/port: Fix use after free of parent_port in cxl_detach_ep() Date: Tue, 31 Mar 2026 18:18:24 +0200 Message-ID: <20260331161753.527546911@linuxfoundation.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260331161753.468533260@linuxfoundation.org> References: <20260331161753.468533260@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 6.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Alison Schofield [ Upstream commit 19d2f0b97a131198efc2c4ca3eb7f980bba8c2b4 ] cxl_detach_ep() is called during bottom-up removal when all CXL memory devices beneath a switch port have been removed. For each port in the hierarchy it locks both the port and its parent, removes the endpoint, and if the port is now empty, marks it dead and unregisters the port by calling delete_switch_port(). There are two places during this work where the parent_port may be used after freeing: First, a concurrent detach may have already processed a port by the time a second worker finds it via bus_find_device(). Without pinning parent_port, it may already be freed when we discover port->dead and attempt to unlock the parent_port. In a production kernel that's a silent memory corruption, with lock debug, it looks like this: []DEBUG_LOCKS_WARN_ON(__owner_task(owner) != get_current()) []WARNING: kernel/locking/mutex.c:949 at __mutex_unlock_slowpath+0x1ee/0x310 []Call Trace: []mutex_unlock+0xd/0x20 []cxl_detach_ep+0x180/0x400 [cxl_core] []devm_action_release+0x10/0x20 []devres_release_all+0xa8/0xe0 []device_unbind_cleanup+0xd/0xa0 []really_probe+0x1a6/0x3e0 Second, delete_switch_port() releases three devm actions registered against parent_port. The last of those is unregister_port() and it calls device_unregister() on the child port, which can cascade. If parent_port is now also empty the device core may unregister and free it too. So by the time delete_switch_port() returns, parent_port may be free, and the subsequent device_unlock(&parent_port->dev) operates on freed memory. The kernel log looks same as above, with a different offset in cxl_detach_ep(). Both of these issues stem from the absence of a lifetime guarantee between a child port and its parent port. Establish a lifetime rule for ports: child ports hold a reference to their parent device until release. Take the reference when the port is allocated and drop it when released. This ensures the parent is valid for the full lifetime of the child and eliminates the use after free window in cxl_detach_ep(). This is easily reproduced with a reload of cxl_acpi in QEMU with CXL devices present. Fixes: 2345df54249c ("cxl/memdev: Fix endpoint port removal") Reviewed-by: Dave Jiang Reviewed-by: Li Ming Signed-off-by: Alison Schofield Reviewed-by: Jonathan Cameron Link: https://patch.msgid.link/20260226184439.1732841-1-alison.schofield@intel.com Signed-off-by: Dave Jiang Signed-off-by: Sasha Levin --- drivers/cxl/core/port.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff --git a/drivers/cxl/core/port.c b/drivers/cxl/core/port.c index 85131872d7f6e..c53a13d4f1662 100644 --- a/drivers/cxl/core/port.c +++ b/drivers/cxl/core/port.c @@ -553,10 +553,13 @@ static void cxl_port_release(struct device *dev) xa_destroy(&port->dports); xa_destroy(&port->regions); ida_free(&cxl_port_ida, port->id); - if (is_cxl_root(port)) + + if (is_cxl_root(port)) { kfree(to_cxl_root(port)); - else + } else { + put_device(dev->parent); kfree(port); + } } static ssize_t decoders_committed_show(struct device *dev, @@ -722,6 +725,7 @@ static struct cxl_port *cxl_port_alloc(struct device *uport_dev, struct cxl_port *iter; dev->parent = &parent_port->dev; + get_device(dev->parent); port->depth = parent_port->depth + 1; port->parent_dport = parent_dport; -- 2.51.0