virSecuritySELinuxSetFileconHelper: Don't fail on read-only NFS

https://bugzilla.redhat.com/show_bug.cgi?id=996543

When starting up a domain, the SELinux labeling is done depending on
current configuration. If the labeling fails we check for possible
causes, as not all labeling failures are fatal. For example, if the
labeled file is on NFS which lacks SELinux support, the file can still
be readable to qemu process. These cases are distinguished by the errno
code: NFS without SELinux support returns EOPNOTSUPP. However, we were
missing one scenario. In case there's a read-only disk on a read-only
NFS (and possibly any FS) and the labeling is just optional (not
explicitly requested in the XML) there's no need to make the labeling
error fatal. In other words, read-only file on read-only NFS can fail to
be labeled, but be readable at the same time.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>

diff --git a/src/security/security_selinux.c b/src/security/security_selinux.c
index 11c0c3bd99387276ba0d8cd00737286f525ca570..c70ac773f3b688c009c9366a4d692f9f5aa379f1 100644 (file)
--- a/src/security/security_selinux.c
+++ b/src/security/security_selinux.c
@@ -896,13 +896,14 @@ virSecuritySELinuxSetFileconHelper(const char *path, char *tcon, bool optional)
             freecon(econ);
         }
 
-        /* if the error complaint is related to an image hosted on
-         * an nfs mount, or a usbfs/sysfs filesystem not supporting
-         * labelling, then just ignore it & hope for the best.
-         * The user hopefully set one of the necessary SELinux
-         * virt_use_{nfs,usb,pci}  boolean tunables to allow it...
+        /* If the error complaint is related to an image hosted on a (possibly
+         * read-only) NFS mount, or a usbfs/sysfs filesystem not supporting
+         * labelling, then just ignore it & hope for the best.  The user
+         * hopefully sets one of the necessary SELinux virt_use_{nfs,usb,pci}
+         * boolean tunables to allow it ...
          */
-        if (setfilecon_errno != EOPNOTSUPP && setfilecon_errno != ENOTSUP) {
+        if (setfilecon_errno != EOPNOTSUPP && setfilecon_errno != ENOTSUP &&
+            setfilecon_errno != EROFS) {
             virReportSystemError(setfilecon_errno,
                                  _("unable to set security context '%s' on '%s'"),
                                  tcon, path);