[PATCH] usb/hcd-xhci: Fix an index-out-of-bounds in xhci_runtime_write and xhci_runtime_read

[AlexChen]

Currently, the 'v' is not checked whether it is between 0 and 16,
which may result in an out-of-bounds access to the array 'xhci->intr[]'.
This is LP#1902112. Following is the reproducer provided in:
-->https://bugs.launchpad.net/qemu/+bug/1902112

=== Reproducer (build with --enable-sanitizers) ===
export UBSAN_OPTIONS="print_stacktrace=1:silence_unsigned_overflow=1"
cat << EOF | ./qemu-system-i386 -display none -machine\
 accel=qtest, -m 512M -machine q35 -nodefaults -drive\
 file=null-co://,if=none,format=raw,id=disk0 -device\
 qemu-xhci,id=xhci -device usb-tablet,bus=xhci.0\
 -device usb-bot -device usb-storage,drive=disk0\
 -chardev null,id=cd0 -chardev null,id=cd1 -device\
 usb-braille,chardev=cd0 -device usb-ccid -device\
 usb-ccid -device usb-kbd -device usb-mouse -device\
 usb-serial,chardev=cd1 -device usb-tablet -device\
 usb-wacom-tablet -device usb-audio -qtest stdio
outl 0xcf8 0x80000803
outl 0xcfc 0x18caffff
outl 0xcf8 0x80000810
outl 0xcfc 0x555a2e46
write 0x555a1004 0x4 0xe7b9aa7a
EOF

=== Stack Trace ===

SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior 
../hw/usb/hcd-xhci.c:3012:30 in
../hw/usb/hcd-xhci.c:3012:30: runtime error: index -1 out of bounds for type 
'XHCIInterrupter [16]'
#0 0x55bd2e97c8b0 in xhci_runtime_write /src/qemu/hw/usb/hcd-xhci.c:3012:30
#1 0x55bd2edfdd13 in memory_region_write_accessor 
/src/qemu/softmmu/memory.c:484:5
#2 0x55bd2edfdb14 in access_with_adjusted_size /src/qemu/softmmu/memory.c:545:18
#3 0x55bd2edfd54b in memory_region_dispatch_write 
/src/qemu/softmmu/memory.c:0:13
#4 0x55bd2ed7fa46 in flatview_write_continue /src/qemu/softmmu/physmem.c:2767:23
#5 0x55bd2ed7cac0 in flatview_write /src/qemu/softmmu/physmem.c:2807:14

This patch fixes this bug.

Buglink: https://bugs.launchpad.net/qemu/+bug/1902112
Reported-by: Alexander Bulekov <alxndr@bu.edu>
Signed-off-by: Alex Chen <alex.chen@huawei.com>
---
 hw/usb/hcd-xhci.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/hw/usb/hcd-xhci.c b/hw/usb/hcd-xhci.c
index 79ce5c4be6..50abef40ad 100644
--- a/hw/usb/hcd-xhci.c
+++ b/hw/usb/hcd-xhci.c
@@ -2962,8 +2962,9 @@ static uint64_t xhci_runtime_read(void *ptr, hwaddr reg,
 {
     XHCIState *xhci = ptr;
     uint32_t ret = 0;
+    int v = (reg - 0x20) / 0x20;

-    if (reg < 0x20) {
+    if (reg < 0x20 || v < 0 || v >= XHCI_MAXINTRS) {
         switch (reg) {
         case 0x00: /* MFINDEX */
             ret = xhci_mfindex_get(xhci) & 0x3fff;
@@ -2973,7 +2974,6 @@ static uint64_t xhci_runtime_read(void *ptr, hwaddr reg,
             break;
         }
     } else {
-        int v = (reg - 0x20) / 0x20;
         XHCIInterrupter *intr = &xhci->intr[v];
         switch (reg & 0x1f) {
         case 0x00: /* IMAN */
@@ -3009,14 +3009,16 @@ static void xhci_runtime_write(void *ptr, hwaddr reg,
 {
     XHCIState *xhci = ptr;
     int v = (reg - 0x20) / 0x20;
-    XHCIInterrupter *intr = &xhci->intr[v];
+    XHCIInterrupter *intr;
     trace_usb_xhci_runtime_write(reg, val);

-    if (reg < 0x20) {
+    if (reg < 0x20 || v < 0 || v >= XHCI_MAXINTRS) {
         trace_usb_xhci_unimplemented("runtime write", reg);
         return;
     }

+    intr = &xhci->intr[v];
+
     switch (reg & 0x1f) {
     case 0x00: /* IMAN */
         if (val & IMAN_IP) {
-- 
2.19.1