[Xen-changelog] [xen-unstable] libxc: Check there's enough memory for segments we're creating

[Xen patchbot-unstable <patchbot-unstable@xxxxxxxxxxxxxxxxxxx>]

# HG changeset patch
# User Keir Fraser <keir.fraser@xxxxxxxxxx>
# Date 1265190361 0
# Node ID 7a10f8513b3f155c4771e7f560ad69cc5deaacb0
# Parent  02107eca8fb7e8acc6332a67e0781414ad71eeeb
libxc: Check there's enough memory for segments we're creating

Previously, xc_dom_alloc_segment would go ahead even if the segment
we're trying to create is too big for the domain's RAM (or the
requested addr is out of range).  It would pass invalid parameters to
xc_dom_seg_to_ptr giving undefined behaviour.

Fixing xc_dom_seg_to_ptr to fail is not sufficient because we want to
provide a comprehensible explanation to the caller - which may
ultimately be the user.

In particular, with this change attempting "xl create" with a ramdisk
image bigger than the guest's specified RAM will provide a useful
error message mentioning the ramdisk.

Signed-off-by: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
---
 tools/libxc/xc_dom_core.c |   13 ++++++++++++-
 1 files changed, 12 insertions(+), 1 deletion(-)

diff -r 02107eca8fb7 -r 7a10f8513b3f tools/libxc/xc_dom_core.c
--- a/tools/libxc/xc_dom_core.c Wed Feb 03 09:45:40 2010 +0000
+++ b/tools/libxc/xc_dom_core.c Wed Feb 03 09:46:01 2010 +0000
@@ -409,8 +409,19 @@ int xc_dom_alloc_segment(struct xc_dom_i
     }
 
     seg->vstart = start;
+    seg->pfn = (seg->vstart - dom->parms.virt_base) / page_size;
+
+    if ( pages > dom->total_pages || /* double test avoids overflow probs */
+         pages > dom->total_pages - seg->pfn)
+    {
+        xc_dom_panic(XC_OUT_OF_MEMORY,
+                     "%s: segment %s too large (0x%"PRIpfn" > "
+                     "0x%"PRIpfn" - 0x%"PRIpfn" pages)\n",
+                     __FUNCTION__, name, pages, dom->total_pages, seg->pfn);
+        return -1;
+    }
+
     seg->vend = start + pages * page_size;
-    seg->pfn = (seg->vstart - dom->parms.virt_base) / page_size;
     dom->virt_alloc_end = seg->vend;
     if (dom->allocate)
         dom->allocate(dom, dom->virt_alloc_end);

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