From 40b76f1fb04af421c1415f7bcb168dfaa6960d0d Mon Sep 17 00:00:00 2001 From: Ian Jackson Date: Fri, 14 Jun 2013 16:45:40 +0100 Subject: 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 --- tools/libxc/xc_dom_binloader.c | 15 +++++++++++++-- 1 file changed, 13 insertions(+), 2 deletions(-) diff --git a/tools/libxc/xc_dom_binloader.c b/tools/libxc/xc_dom_binloader.c index bde93f7184..8596a2804c 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); -- cgit v1.2.3