[Qemu-stable] [PATCH] i8254: fix out-of-bounds memory access in pit_ioport_read()

[Petr Matousek]

Due converting PIO to the new memory read/write api we no longer provide
separate I/O region lenghts for read and write operations. As a result,
reading from PIT Mode/Command register will end with accessing
pit->channels with invalid index.

Fix this by ignoring read from the Mode/Command register.

This is CVE-2015-3214.

Signed-off-by: Petr Matousek <address@hidden>
Reported-by: Matt Tait <address@hidden>
---
 hw/timer/i8254.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/hw/timer/i8254.c b/hw/timer/i8254.c
index 3450c98..9b65a33 100644
--- a/hw/timer/i8254.c
+++ b/hw/timer/i8254.c
@@ -196,6 +196,12 @@ static uint64_t pit_ioport_read(void *opaque, hwaddr addr,
     PITChannelState *s;
 
     addr &= 3;
+
+    if (addr == 3) {
+        /* Mode/Command register is write only, read is ignored */
+        return 0;
+    }
+
     s = &pit->channels[addr];
     if (s->status_latched) {
         s->status_latched = 0;
-- 
2.1.0