[Xen-changelog] [xen-unstable] xend: Actually restrict a domU's access to xenstore when we mean to --

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

# HG changeset patch
# User Keir Fraser <keir.fraser@xxxxxxxxxx>
# Date 1229620708 0
# Node ID 8c35da364ab39605839869d8eb0ac9b831c370f0
# Parent  54c5d8247aaf0f4fed9f3fa794f7bf57009808f8
xend: Actually restrict a domU's access to xenstore when we mean to --
this means that in some cases it cannot be owner of its own xenstore
nodes.

This bug was pointed out by Daniel Berrange at Red Hat. This patch is
my own more generic fix that automatically covers a range of callers
(albeit the patch is arguably a bit of a hack ;-).

Signed-off-by: Keir Fraser <keir.fraser@xxxxxxxxxx>
---
 tools/python/xen/lowlevel/xs/xs.c |   17 ++++++++++++++++-
 1 files changed, 16 insertions(+), 1 deletion(-)

diff -r 54c5d8247aaf -r 8c35da364ab3 tools/python/xen/lowlevel/xs/xs.c
--- a/tools/python/xen/lowlevel/xs/xs.c Thu Dec 18 17:14:27 2008 +0000
+++ b/tools/python/xen/lowlevel/xs/xs.c Thu Dec 18 17:18:28 2008 +0000
@@ -336,15 +336,19 @@ static PyObject *xspy_set_permissions(Xs
        xs_set_error(EINVAL);
         goto exit;
     }
+
     xsperms_n = PyList_Size(perms);
-    xsperms = calloc(xsperms_n, sizeof(struct xs_permissions));
+    /* NB. alloc +1 so we can change the owner if necessary. */
+    xsperms = calloc(xsperms_n + 1, sizeof(struct xs_permissions));
     if (!xsperms) {
        xs_set_error(ENOMEM);
         goto exit;
     }
+
     tuple0 = PyTuple_New(0);
     if (!tuple0)
         goto exit;
+
     for (i = 0; i < xsperms_n; i++) {
         /* Read/write perms. Set these. */
         int p_read = 0, p_write = 0;
@@ -357,6 +361,17 @@ static PyObject *xspy_set_permissions(Xs
         if (p_write)
             xsperms[i].perms |= XS_PERM_WRITE;
     }
+
+    /*
+     * Is the caller trying to restrict access to the first specified
+     * domain? If so then it cannot be owner, so we force dom0 as owner.
+     */
+    if (xsperms_n && xsperms[0].perms && xsperms[0].id) {
+        memmove(&xsperms[1], &xsperms[0], xsperms_n * sizeof(*xsperms));
+        xsperms[0].id = xsperms[0].perms = 0;
+        xsperms_n++;
+    }
+
     Py_BEGIN_ALLOW_THREADS
     result = xs_set_permissions(xh, th, path, xsperms, xsperms_n);
     Py_END_ALLOW_THREADS

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