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[Xen-changelog] [xen master] libxc: Add range checking to xc_dom_binloader

commit 2bcee4b3c316379f4b52cb308947eb6db3faf1a0
Author:     Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
AuthorDate: Fri Jun 14 16:39:37 2013 +0100
Commit:     Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>
CommitDate: Fri Jun 14 16:39:37 2013 +0100

    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@xxxxxxxxxxxxx>
    Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Reviewed-by: George Dunlap <george.dunlap@xxxxxxxxxxxxx>
    v9: Use clearer code for calculating probe_end in find_table.
    v6: Add a missing `return -EINVAL' (Matthew Daley).
        Fix an error in the commit message (Matthew Daley).
    v5: This patch is new in this version of the series.
 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 d2de04c..6469a65 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);
generated by git-patchbot for /home/xen/git/xen.git#master

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