linux-kernel - [PATCH v2] drivers: usb: host: fix NULL pointer dereferences triggered by unhandled errors in xhci_create_rhub_port

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Message-Id: <20220421133902.1132063-1-r33s3n6@gmail.com>
Date:   Thu, 21 Apr 2022 21:39:02 +0800
From:   Zixuan Fu <r33s3n6@...il.com>
To:     mathias.nyman@...el.com, gregkh@...uxfoundation.org
Cc:     linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        baijiaju1990@...il.com, Zixuan Fu <r33s3n6@...il.com>,
        TOTE Robot <oslab@...nghua.edu.cn>
Subject: [PATCH v2] drivers: usb: host: fix NULL pointer dereferences triggered by unhandled errors in xhci_create_rhub_port_array()

In xhci_create_rhub_port_array(), when rhub->num_ports is zero, 
rhub->ports would not be set; when kcalloc_node() fails, rhub->ports
would be set to NULL. In these two cases, xhci_create_rhub_port_array()
just returns void, and thus its callers are unaware of the error.

Then rhub->ports is dereferenced in xhci_usb3_hub_descriptor() or 
xhci_usb2_hub_descriptor().

To fix the bug, xhci_setup_port_arrays() should return an integer to 
indicate a possible error, and its callers should handle the error.

In the driver, xhci_create_rhub_port_array() is only used in 
xhci_setup_port_arrays(), and only xhci_mem_init() calls
xhci_setup_port_arrays() and does all cleanup work when it fails.
Specifically, xhci_mem_init() calls xhci_mem_cleanup(), which eventually
calls kfree(xhci->usb2_rhub.ports) and kfree(xhci->usb3_rhub.ports). For
this reason, when xhci_create_rhub_port_array() fails, 
xhci_setup_port_arrays() should return the error code directly, without
freeing the memory allocated in this function.

The error log in our fault-injection testing is shown as follows:

[   24.001309] BUG: kernel NULL pointer dereference, address: 0000000000000000
...
[   24.003992] RIP: 0010:xhci_hub_control+0x3f5/0x60d0 [xhci_hcd]
...
[   24.009803] Call Trace:
[   24.010014]  <TASK>
[   24.011310]  usb_hcd_submit_urb+0x1233/0x1fd0
[   24.017071]  usb_start_wait_urb+0x115/0x310
[   24.017641]  usb_control_msg+0x28a/0x450
[   24.019046]  hub_probe+0xb16/0x2320
[   24.019757]  usb_probe_interface+0x4f1/0x930
[   24.019765]  really_probe+0x33d/0x970
[   24.019768]  __driver_probe_device+0x157/0x210
[   24.019772]  driver_probe_device+0x4f/0x340
[   24.019775]  __device_attach_driver+0x2ee/0x3a0
...

Reported-by: TOTE Robot <oslab@...nghua.edu.cn>
Signed-off-by: Zixuan Fu <r33s3n6@...il.com>
---
v2:
* Explain the reason why xhci_setup_port_arrays() returns without freeing the memory in error handling code.
  Thank Greg KH for helpful advice.
---
 drivers/usb/host/xhci-mem.c | 17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)

diff --git a/drivers/usb/host/xhci-mem.c b/drivers/usb/host/xhci-mem.c
index bbb27ee2c6a3..024515346c39 100644
--- a/drivers/usb/host/xhci-mem.c
+++ b/drivers/usb/host/xhci-mem.c
@@ -2235,7 +2235,7 @@ static void xhci_add_in_port(struct xhci_hcd *xhci, unsigned int num_ports,
 	/* FIXME: Should we disable ports not in the Extended Capabilities? */
 }
 
-static void xhci_create_rhub_port_array(struct xhci_hcd *xhci,
+static int xhci_create_rhub_port_array(struct xhci_hcd *xhci,
 					struct xhci_hub *rhub, gfp_t flags)
 {
 	int port_index = 0;
@@ -2243,11 +2243,11 @@ static void xhci_create_rhub_port_array(struct xhci_hcd *xhci,
 	struct device *dev = xhci_to_hcd(xhci)->self.sysdev;
 
 	if (!rhub->num_ports)
-		return;
+		return -EINVAL;
 	rhub->ports = kcalloc_node(rhub->num_ports, sizeof(*rhub->ports),
 			flags, dev_to_node(dev));
 	if (!rhub->ports)
-		return;
+		return -ENOMEM;
 
 	for (i = 0; i < HCS_MAX_PORTS(xhci->hcs_params1); i++) {
 		if (xhci->hw_ports[i].rhub != rhub ||
@@ -2259,6 +2259,7 @@ static void xhci_create_rhub_port_array(struct xhci_hcd *xhci,
 		if (port_index == rhub->num_ports)
 			break;
 	}
+	return 0;
 }
 
 /*
@@ -2277,6 +2278,7 @@ static int xhci_setup_port_arrays(struct xhci_hcd *xhci, gfp_t flags)
 	int cap_count = 0;
 	u32 cap_start;
 	struct device *dev = xhci_to_hcd(xhci)->self.sysdev;
+	int ret;
 
 	num_ports = HCS_MAX_PORTS(xhci->hcs_params1);
 	xhci->hw_ports = kcalloc_node(num_ports, sizeof(*xhci->hw_ports),
@@ -2367,8 +2369,13 @@ static int xhci_setup_port_arrays(struct xhci_hcd *xhci, gfp_t flags)
 	 * Not sure how the USB core will handle a hub with no ports...
 	 */
 
-	xhci_create_rhub_port_array(xhci, &xhci->usb2_rhub, flags);
-	xhci_create_rhub_port_array(xhci, &xhci->usb3_rhub, flags);
+	ret = xhci_create_rhub_port_array(xhci, &xhci->usb2_rhub, flags);
+	if (ret)
+		return ret;
+
+	ret = xhci_create_rhub_port_array(xhci, &xhci->usb3_rhub, flags);
+	if (ret)
+		return ret;
 
 	return 0;
 }
-- 
2.25.1