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Re: [libvirt] [PATCH] Fix crash in SELinuxSecurityVerify



On 01/13/2011 08:46 AM, Daniel P. Berrange wrote:
On Thu, Jan 13, 2011 at 12:30:30AM -0500, Laine Stump wrote:
When attempting to edit a domain, libvirtd segfaulted in
SELinuxSecurityVerify() on this line:

   if (!STREQ(virSecurityManagerGetModel(mgr), secdef->model)) {

because secdef->model was NULL. Although I'm too tired to investigate
in depth, I noticed that all the other functions in that file that do
the same STREQ() will first check that def->seclabel.label is
non-NULL, but this function doesn't. I also noticed that label *is*
NULL in my case, so I tried adding that check to
SELinuxSecurityVerify(), and the crash goes away.

I have no idea if this is the correct fix, but it allowed me to
continue my testing of a new (unrelated) feature.
---
  src/security/security_selinux.c |    4 ++++
  1 files changed, 4 insertions(+), 0 deletions(-)

diff --git a/src/security/security_selinux.c b/src/security/security_selinux.c
index d06afde..b97ca4c 100644
--- a/src/security/security_selinux.c
+++ b/src/security/security_selinux.c
@@ -871,6 +871,10 @@ SELinuxSecurityVerify(virSecurityManagerPtr mgr ATTRIBUTE_UNUSED,
                        virDomainDefPtr def)
  {
      const virSecurityLabelDefPtr secdef =&def->seclabel;
+
+    if (def->seclabel.label == NULL)
+        return 0;
+
      if (!STREQ(virSecurityManagerGetModel(mgr), secdef->model)) {
          virSecurityReportError(VIR_ERR_INTERNAL_ERROR,
                                 _("security label driver mismatch: "
We don't want to skip a NULL label, but rather a NULL model.

Yeah, it didn't really make sense at the time, but all the other functions were doing it, it stopped the crash, and I was too tired to spend brain cells understanding the code :-)

So I think you actually need to add a check

   if (def->seclabel.model == NULL)
     return 0;

but in the Verify method in src/security/security_manager.c so
that all drivers are protected instead of just SELinux.

Okay. Is that needed for the other methods that end up comparing secdef->model, too? Or are you guaranteed a non-null model by the time you get into any of those? (eg virSecurityManagerSetProcessLabel(), virSecurityManagerSetSecuritySocketLabel(),etc)


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