libxc: builder: limit maximum size of kernel/ramdisk.

Allowing user supplied kernels of arbitrary sizes, especially during
decompression, can swallow up dom0 memory leading to either virtual
address space exhaustion in the builder process or allocation
failures/OOM killing of both toolstack and unrelated processes.

We disable these checks when building in a stub domain for pvgrub
since this uses the guest's own memory and is isolated.

Decompression of gzip compressed kernels and ramdisks has been safe
since 14954:58205257517d (Xen 3.1.0 onwards).

This is XSA-25 / CVE-2012-4544.

Also make explicit checks for buffer overflows in various
decompression routines. These were already ruled out due to other
properties of the code but check them as a belt-and-braces measure.

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>

1 files changed, 22 insertions, 1 deletions

diff --git a/tools/libxc/xc_dom.h b/tools/libxc/xc_dom.h
index 3cd6dae6d6..eccc516c2c 100644
--- a/tools/libxc/xc_dom.h
+++ b/tools/libxc/xc_dom.h
@@ -55,6 +55,9 @@ struct xc_dom_image {
     void *ramdisk_blob;
     size_t ramdisk_size;
 
+    size_t max_kernel_size;
+    size_t max_ramdisk_size;
+
     /* arguments and parameters */
     char *cmdline;
     uint32_t f_requested[XENFEAT_NR_SUBMAPS];
@@ -194,6 +197,23 @@ void xc_dom_release_phys(struct xc_dom_image *dom);
 void xc_dom_release(struct xc_dom_image *dom);
 int xc_dom_mem_init(struct xc_dom_image *dom, unsigned int mem_mb);
 
+/* Set this larger if you have enormous ramdisks/kernels. Note that
+ * you should trust all kernels not to be maliciously large (e.g. to
+ * exhaust all dom0 memory) if you do this (see CVE-2012-4544 /
+ * XSA-25). You can also set the default independently for
+ * ramdisks/kernels in xc_dom_allocate() or call
+ * xc_dom_{kernel,ramdisk}_max_size.
+ */
+#ifndef XC_DOM_DECOMPRESS_MAX
+#define XC_DOM_DECOMPRESS_MAX (1024*1024*1024) /* 1GB */
+#endif
+
+int xc_dom_kernel_check_size(struct xc_dom_image *dom, size_t sz);
+int xc_dom_kernel_max_size(struct xc_dom_image *dom, size_t sz);
+
+int xc_dom_ramdisk_check_size(struct xc_dom_image *dom, size_t sz);
+int xc_dom_ramdisk_max_size(struct xc_dom_image *dom, size_t sz);
+
 size_t xc_dom_check_gzip(xc_interface *xch,
                      void *blob, size_t ziplen);
 int xc_dom_do_gunzip(xc_interface *xch,
@@ -254,7 +274,8 @@ void xc_dom_log_memory_footprint(struct xc_dom_image *dom);
 void *xc_dom_malloc(struct xc_dom_image *dom, size_t size);
 void *xc_dom_malloc_page_aligned(struct xc_dom_image *dom, size_t size);
 void *xc_dom_malloc_filemap(struct xc_dom_image *dom,
-                            const char *filename, size_t * size);
+                            const char *filename, size_t * size,
+                            const size_t max_size);
 char *xc_dom_strdup(struct xc_dom_image *dom, const char *str);
 
 /* --- alloc memory pool ------------------------------------------- */