From 892bb2a720de57109f7e8526879069abcaab38bf Mon Sep 17 00:00:00 2001
From: Kevin Wolf <kwolf@redhat.com>
Date: Thu, 16 Jul 2015 16:15:58 +0200
Subject: [PATCH 1/3] ide: Check array bounds before writing to io_buffer
 (CVE-2015-5154)

Message-id: <1437056160-3284-2-git-send-email-kwolf@redhat.com>
Patchwork-id: n/a
O-Subject: [virt-devel] [RHEL/RHEV-7 qemu-kvm(-rhev) EMBARGOED PATCH 1/3] ide:
        Check array bounds before writing to io_buffer (CVE-2015-5154)
Bugzilla: 1243689
RH-Acked-by: Petr Matousek <pmatouse@redhat.com>
RH-Acked-by: John Snow <jsnow@redhat.com>
RH-Acked-by: Stefan Hajnoczi <stefanha@redhat.com>

If the end_transfer_func of a command is called because enough data has
been read or written for the current PIO transfer, and it fails to
correctly call the command completion functions, the DRQ bit in the
status register and s->end_transfer_func may remain set. This allows the
guest to access further bytes in s->io_buffer beyond s->data_end, and
eventually overflowing the io_buffer.

One case where this currently happens is emulation of the ATAPI command
START STOP UNIT.

This patch fixes the problem by adding explicit array bounds checks
before accessing the buffer instead of relying on end_transfer_func to
function correctly.

Cc: qemu-stable@nongnu.org
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
 hw/ide/core.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/hw/ide/core.c b/hw/ide/core.c
index 24a1708..ada26c0 100644
--- a/hw/ide/core.c
+++ b/hw/ide/core.c
@@ -1849,6 +1849,10 @@ void ide_data_writew(void *opaque, uint32_t addr, uint32_t val)
     }
 
     p = s->data_ptr;
+    if (p + 2 > s->data_end) {
+        return;
+    }
+
     *(uint16_t *)p = le16_to_cpu(val);
     p += 2;
     s->data_ptr = p;
@@ -1870,6 +1874,10 @@ uint32_t ide_data_readw(void *opaque, uint32_t addr)
     }
 
     p = s->data_ptr;
+    if (p + 2 > s->data_end) {
+        return 0;
+    }
+
     ret = cpu_to_le16(*(uint16_t *)p);
     p += 2;
     s->data_ptr = p;
@@ -1891,6 +1899,10 @@ void ide_data_writel(void *opaque, uint32_t addr, uint32_t val)
     }
 
     p = s->data_ptr;
+    if (p + 4 > s->data_end) {
+        return;
+    }
+
     *(uint32_t *)p = le32_to_cpu(val);
     p += 4;
     s->data_ptr = p;
@@ -1912,6 +1924,10 @@ uint32_t ide_data_readl(void *opaque, uint32_t addr)
     }
 
     p = s->data_ptr;
+    if (p + 4 > s->data_end) {
+        return 0;
+    }
+
     ret = cpu_to_le32(*(uint32_t *)p);
     p += 4;
     s->data_ptr = p;
-- 
1.8.3.1