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Re: [libvirt] [PATCH 3/4] security: Introduce method for labeling file descriptors of created files



On 06/27/13 20:51, Daniel P. Berrange wrote:
On Wed, Jun 26, 2013 at 03:01:49PM +0200, Peter Krempa wrote:
The method labels the file descriptor even if dynamic labeling/relabeling
is turned off. This is needed for files created by libvirt and then
passed along to qemu as a FD.
---
  src/libvirt_private.syms        |  1 +
  src/security/security_dac.c     |  9 +++++++++
  src/security/security_driver.h  |  4 ++++
  src/security/security_manager.c | 16 ++++++++++++++++
  src/security/security_manager.h |  3 +++
  src/security/security_nop.c     |  1 +
  src/security/security_selinux.c | 21 +++++++++++++++++++++
  src/security/security_stack.c   | 19 +++++++++++++++++++
  8 files changed, 74 insertions(+)


diff --git a/src/security/security_selinux.c b/src/security/security_selinux.c
index 7802dda..5894259 100644
--- a/src/security/security_selinux.c
+++ b/src/security/security_selinux.c
@@ -2446,6 +2446,26 @@ virSecuritySELinuxGetSecurityMountOptions(virSecurityManagerPtr mgr,
      return opts;
  }

+static int
+virSecuritySELinuxSetCreatedFDLabel(virSecurityManagerPtr mgr ATTRIBUTE_UNUSED,
+                                    virDomainDefPtr def,
+                                    int fd)
+{
+    virSecurityLabelDefPtr secdef;
+
+    if ((secdef = virDomainDefGetSecurityLabelDef(def, SECURITY_SELINUX_NAME))) {
+        if (!secdef->imagelabel)
+            secdef->imagelabel = virSecuritySELinuxGenImageLabel(mgr, def);

This is really dubious. None of the methods except for GenSecurityLabel
should be making changes to the secdef state.

There is already an exception: virSecuritySELinuxGetSecurityMountOptions().


+    } else {
+        return -1;
+    }

The style with nested if()s here is not following the pattern used in other
methods here either.

hmmmm ... ok


+
+    if (secdef->imagelabel == NULL)
+        return 0;
+
+    return virSecuritySELinuxFSetFilecon(fd, secdef->imagelabel);
+}


In general I'm not really convinced we should be adding a new method
here, as opposed to making the existing SetImageFDLabel do the right
thing.

I was going to suggest expanding the function prototype with a bool that would allow to choose whether to label the image always or only if relabeling is enabled but looking through the code I noticed that actually every caller would need to have this flag enabled.

There are currently 4 places this method is called:

qemuDumpToFd() - labels a FD of a freshly created file for the memory dump

qemuMigrationToFile() - again a new file FD is labeled, used for (managed) save and dumping of memory

doTunnelMigrate() - the FD's of a pipe used for extracting data into the stream are labeled, again this would probably fail with static labeling.

qemuProcessStart() - the migration FD is labelled on process start.

I think it's safe (and necessary) to relabel these even if relabeling is disabled and thus we can change the function to always label FD's.
Do you agree?


Daniel


Peter




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