xhci: Fix invalid loop check in xhci_free_tt_info()

xhci_free_tt_info() may access the invalid memory when it removes the
last entry but the list is not empty.  Then tt_next reaches to the
list head but it still tries to check the tt_info of that entry.

This patch fixes the bug and cleans up the messy code by rewriting
with a simple list_for_each_entry_safe().

This patch should be backported to kernels as old as 3.2, that contain
the commit 839c817ce67178ca3c7c7ad534c571bba1e69ebe "xhci: Store
information about roothubs and TTs."

Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
Reviewed-by: Oliver Neukum <oneukum@suse.de>
Cc: <stable@vger.kernel.org>

1 files changed, 10 insertions, 29 deletions

diff --git a/drivers/usb/host/xhci-mem.c b/drivers/usb/host/xhci-mem.c
index ec4338eec826..898dfc8bc520 100644
--- a/drivers/usb/host/xhci-mem.c
+++ b/drivers/usb/host/xhci-mem.c
@@ -793,10 +793,9 @@ static void xhci_free_tt_info(struct xhci_hcd *xhci,
                 struct xhci_virt_device *virt_dev,
                 int slot_id)
 {
-        struct list_head *tt;
         struct list_head *tt_list_head;
-        struct list_head *tt_next;
-        struct xhci_tt_bw_info *tt_info;
+        struct xhci_tt_bw_info *tt_info, *next;
+        bool slot_found = false;
 
         /* If the device never made it past the Set Address stage,
          * it may not have the real_port set correctly.
@@ -808,34 +807,16 @@ static void xhci_free_tt_info(struct xhci_hcd *xhci,
         }
 
         tt_list_head = &(xhci->rh_bw[virt_dev->real_port - 1].tts);
-        if (list_empty(tt_list_head))
-                return;
-
-        list_for_each(tt, tt_list_head) {
-                tt_info = list_entry(tt, struct xhci_tt_bw_info, tt_list);
-                if (tt_info->slot_id == slot_id)
+        list_for_each_entry_safe(tt_info, next, tt_list_head, tt_list) {
+                /* Multi-TT hubs will have more than one entry */
+                if (tt_info->slot_id == slot_id) {
+                        slot_found = true;
+                        list_del(&tt_info->tt_list);
+                        kfree(tt_info);
+                } else if (slot_found) {
                         break;
+                }
         }
-        /* Cautionary measure in case the hub was disconnected before we
-         * stored the TT information.
-         */
-        if (tt_info->slot_id != slot_id)
-                return;
-
-        tt_next = tt->next;
-        tt_info = list_entry(tt, struct xhci_tt_bw_info,
-                        tt_list);
-        /* Multi-TT hubs will have more than one entry */
-        do {
-                list_del(tt);
-                kfree(tt_info);
-                tt = tt_next;
-                if (list_empty(tt_list_head))
-                        break;
-                tt_next = tt->next;
-                tt_info = list_entry(tt, struct xhci_tt_bw_info,
-                                tt_list);
-        } while (tt_info->slot_id == slot_id);
 }
 
 int xhci_alloc_tt_info(struct xhci_hcd *xhci,