From 40b76f1fb04af421c1415f7bcb168dfaa6960d0d Mon Sep 17 00:00:00 2001
From: Ian Jackson <ian.jackson@eu.citrix.com>
Date: Fri, 14 Jun 2013 16:45:40 +0100
Subject: [PATCH 17/21] libxc: Add range checking to xc_dom_binloader
This is a simple binary image loader with its own metadata format.
However, it is too careless with image-supplied values.
Add the following checks:
* That the image is bigger than the metadata table; otherwise the
pointer arithmetic to calculate the metadata table location may
yield undefined and dangerous values.
* When clamping the end of the region to search, that we do not
calculate pointers beyond the end of the image. The C
specification does not permit this and compilers are becoming ever
more determined to miscompile code when they can "prove" various
falsehoods based on assertions from the C spec.
* That the supplied image is big enough for the text we are allegedly
copying from it. Otherwise we might have a read overrun and copy
the results (perhaps a lot of secret data) into the guest.
This is part of the fix to a security issue, XSA-55.
Signed-off-by: Ian Jackson <ian.jackson@eu.citrix.com>
---
tools/libxc/xc_dom_binloader.c | 15 +++++++++++++--
1 files changed, 13 insertions(+), 2 deletions(-)
diff --git a/tools/libxc/xc_dom_binloader.c b/tools/libxc/xc_dom_binloader.c
index bde93f7..8596a28 100644
--- a/tools/libxc/xc_dom_binloader.c
+++ b/tools/libxc/xc_dom_binloader.c
@@ -123,10 +123,13 @@ static struct xen_bin_image_table *find_table(struct xc_dom_image *dom)
uint32_t *probe_ptr;
uint32_t *probe_end;
+ if ( dom->kernel_size < sizeof(*table) )
+ return NULL;
probe_ptr = dom->kernel_blob;
- probe_end = dom->kernel_blob + dom->kernel_size - sizeof(*table);
- if ( (void*)probe_end > (dom->kernel_blob + 8192) )
+ if ( dom->kernel_size > (8192 + sizeof(*table)) )
probe_end = dom->kernel_blob + 8192;
+ else
+ probe_end = dom->kernel_blob + dom->kernel_size - sizeof(*table);
for ( table = NULL; probe_ptr < probe_end; probe_ptr++ )
{
@@ -282,6 +285,14 @@ static int xc_dom_load_bin_kernel(struct xc_dom_image *dom)
return -EINVAL;
}
+ if ( image_size < skip ||
+ image_size - skip < text_size )
+ {
+ DOMPRINTF("%s: image is too small for declared text size",
+ __FUNCTION__);
+ return -EINVAL;
+ }
+
memcpy(dest, image + skip, text_size);
memset(dest + text_size, 0, bss_size);
--
1.7.2.5