It may happen that we leave some XATTRs behind. For instance, on
a sudden power loss, the host just shuts down without calling
restore on domain paths. This creates a problem, because when the
host starts up again, the XATTRs are there but they don't reflect
the true state and this may result in libvirt denying start of a
domain.

To solve this, save a unique timestamp among with our XATTRs. The
timestamp consists of host UUID + boot timestamp.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
---
 src/security/security_util.c | 202 ++++++++++++++++++++++++++++++++++-
 tests/qemusecuritymock.c     |  12 +++
 2 files changed, 213 insertions(+), 1 deletion(-)

diff --git a/src/security/security_util.c b/src/security/security_util.c
index 365b2dd2d6..d063f526be 100644
--- a/src/security/security_util.c
+++ b/src/security/security_util.c
@@ -22,11 +22,16 @@
 #include "virfile.h"
 #include "virstring.h"
 #include "virerror.h"
+#include "virlog.h"
+#include "viruuid.h"
+#include "virhostuptime.h"
 
 #include "security_util.h"
 
 #define VIR_FROM_THIS VIR_FROM_SECURITY
 
+VIR_LOG_INIT("security.security_util");
+
 /* There are four namespaces available on Linux (xattr(7)):
  *
  *  user - can be modified by anybody,
@@ -83,6 +88,157 @@ virSecurityGetRefCountAttrName(const char *name ATTRIBUTE_UNUSED)
 }
 
 
+static char *
+virSecurityGetTimestampAttrName(const char *name ATTRIBUTE_UNUSED)
+{
+    char *ret = NULL;
+#ifdef XATTR_NAMESPACE
+    ignore_value(virAsprintf(&ret, XATTR_NAMESPACE".libvirt.security.timestamp_%s", name));
+#else
+    errno = ENOSYS;
+    virReportSystemError(errno, "%s",
+                         _("Extended attributes are not supported on this system"));
+#endif
+    return ret;
+}
+
+
+/* This global timestamp holds combination of host UUID + boot time so that we
+ * can detect stale XATTRs. For instance, on a sudden power loss, XATTRs are
+ * not going to change (nobody will call restoreLabel()) and thus they reflect
+ * state from just before the power loss and if there was a machine running,
+ * then XATTRs there are stale and no one will ever remove them. They don't
+ * reflect the true state (most notably the ref counter).
+ */
+static char *timestamp;
+
+
+static int
+virSecurityEnsureTimestamp(void)
+{
+    unsigned char uuid[VIR_UUID_BUFLEN] = {0};
+    char uuidstr[VIR_UUID_STRING_BUFLEN] = {0};
+    unsigned long long boottime = 0;
+
+    if (timestamp)
+        return 0;
+
+    if (virGetHostUUID(uuid) < 0) {
+        virReportError(VIR_ERR_INTERNAL_ERROR,
+                       "%s", _("cannot get the host uuid"));
+        return -1;
+    }
+
+    virUUIDFormat(uuid, uuidstr);
+
+    if (virHostGetBootTime(&boottime) < 0) {
+        virReportSystemError(errno, "%s",
+                             _("Unable to get host boot time"));
+        return -1;
+    }
+
+    if (virAsprintf(&timestamp, "%s-%llu", uuidstr, boottime) < 0)
+        return -1;
+
+    return 0;
+}
+
+
+/**
+ * virSecurityValidateTimestamp:
+ * @name: security driver name
+ * @path: file name
+ *
+ * Check if remembered label on @path for security driver @name
+ * is valid, i.e. the label has been set since the last boot. If
+ * the label was set in previous runs, all XATTRs related to
+ * @name are removed so that clean slate is restored.
+ *
+ * Returns: 0 if remembered label is valid,
+ *          1 if remembered label was not valid,
+ *         -1 otherwise.
+ */
+static int
+virSecurityValidateTimestamp(const char *name,
+                             const char *path)
+{
+    VIR_AUTOFREE(char *) timestamp_name = NULL;
+    VIR_AUTOFREE(char *) value = NULL;
+
+    if (virSecurityEnsureTimestamp() < 0)
+        return -1;
+
+    if (!(timestamp_name = virSecurityGetTimestampAttrName(name)))
+        return -1;
+
+    errno = 0;
+    if (virFileGetXAttrQuiet(path, timestamp_name, &value) < 0) {
+        if (errno == ENOSYS || errno == ENOTSUP) {
+            /* XATTRs are not supported. */
+            return -1;
+        } else if (errno != ENODATA) {
+            virReportSystemError(errno,
+                                 _("Unable to get XATTR %s on %s"),
+                                 timestamp_name,
+                                 path);
+            return -1;
+        }
+
+        /* Timestamp is missing. We can continue and claim a valid timestamp.
+         * But then we would never remove stale XATTRs. Therefore, claim it
+         * invalid and have the code below remove all XATTRs. This of course
+         * means that we will not restore the original owner, but the plus side
+         * is that we reset refcounter which will represent the true state.
+         */
+    }
+
+    if (STREQ_NULLABLE(value, timestamp)) {
+        /* Hooray, XATTRs are valid. */
+        VIR_DEBUG("XATTRs on %s secdriver=%s are valid", path, name);
+        return 0;
+    }
+
+    VIR_WARN("Invalid XATTR timestamp detected on %s secdriver=%s", path, name);
+
+    if (virSecurityMoveRememberedLabel(name, path, NULL) < 0)
+        return -1;
+
+    return 1;
+}
+
+
+static int
+virSecurityAddTimestamp(const char *name,
+                        const char *path)
+{
+    VIR_AUTOFREE(char *) timestamp_name = NULL;
+
+    if (virSecurityEnsureTimestamp() < 0)
+        return -1;
+
+    if (!(timestamp_name = virSecurityGetTimestampAttrName(name)))
+        return -1;
+
+    return virFileSetXAttr(path, timestamp_name, timestamp);
+}
+
+
+static int
+virSecurityRemoveTimestamp(const char *name,
+                           const char *path)
+{
+    VIR_AUTOFREE(char *) timestamp_name = NULL;
+
+    if (!(timestamp_name = virSecurityGetTimestampAttrName(name)))
+        return -1;
+
+    if (virFileRemoveXAttr(path, timestamp_name) < 0 && errno != ENOENT)
+        return -1;
+
+    return 0;
+}
+
+
 /**
  * virSecurityGetRememberedLabel:
  * @name: security driver name
@@ -120,6 +276,12 @@ virSecurityGetRememberedLabel(const char *name,
 
     *label = NULL;
 
+    if (virSecurityValidateTimestamp(name, path) < 0) {
+        if (errno == ENOSYS || errno == ENOTSUP)
+            return -2;
+        return -1;
+    }
+
     if (!(ref_name = virSecurityGetRefCountAttrName(name)))
         return -1;
 
@@ -163,6 +325,9 @@ virSecurityGetRememberedLabel(const char *name,
 
         if (virFileRemoveXAttr(path, attr_name) < 0)
             return -1;
+
+        if (virSecurityRemoveTimestamp(name, path) < 0)
+            return -1;
     }
 
     return 0;
@@ -199,6 +364,12 @@ virSecuritySetRememberedLabel(const char *name,
     VIR_AUTOFREE(char *) value = NULL;
     unsigned int refcount = 0;
 
+    if (virSecurityValidateTimestamp(name, path) < 0) {
+        if (errno == ENOSYS || errno == ENOTSUP)
+            return -2;
+        return -1;
+    }
+
     if (!(ref_name = virSecurityGetRefCountAttrName(name)))
         return -1;
 
@@ -232,6 +403,9 @@ virSecuritySetRememberedLabel(const char *name,
 
         if (virFileSetXAttr(path, attr_name, label) < 0)
             return -1;
+
+        if (virSecurityAddTimestamp(name, path) < 0)
+            return -1;
     }
 
     if (virAsprintf(&value, "%u", refcount) < 0)
@@ -266,9 +440,12 @@ virSecurityMoveRememberedLabel(const char *name,
     VIR_AUTOFREE(char *) ref_value = NULL;
     VIR_AUTOFREE(char *) attr_name = NULL;
     VIR_AUTOFREE(char *) attr_value = NULL;
+    VIR_AUTOFREE(char *) timestamp_name = NULL;
+    VIR_AUTOFREE(char *) timestamp_value = NULL;
 
     if (!(ref_name = virSecurityGetRefCountAttrName(name)) ||
-        !(attr_name = virSecurityGetAttrName(name)))
+        !(attr_name = virSecurityGetAttrName(name)) ||
+        !(timestamp_name = virSecurityGetTimestampAttrName(name)))
         return -1;
 
     if (virFileGetXAttrQuiet(src, ref_name, &ref_value) < 0) {
@@ -293,6 +470,17 @@ virSecurityMoveRememberedLabel(const char *name,
         }
     }
 
+    if (virFileGetXAttrQuiet(src, timestamp_name, &timestamp_value) < 0) {
+        if (errno == ENOSYS || errno == ENOTSUP) {
+            return -2;
+        } else if (errno != ENODATA) {
+            virReportSystemError(errno,
+                                 _("Unable to get XATTR %s on %s"),
+                                 attr_name, src);
+            return -1;
+        }
+    }
+
     if (ref_value &&
         virFileRemoveXAttr(src, ref_name) < 0) {
         return -1;
@@ -303,6 +491,11 @@ virSecurityMoveRememberedLabel(const char *name,
         return -1;
     }
 
+    if (timestamp_value &&
+        virFileRemoveXAttr(src, timestamp_name) < 0) {
+        return -1;
+    }
+
     if (dst) {
         if (ref_value &&
             virFileSetXAttr(dst, ref_name, ref_value) < 0) {
@@ -314,6 +507,13 @@ virSecurityMoveRememberedLabel(const char *name,
             ignore_value(virFileRemoveXAttr(dst, ref_name));
             return -1;
         }
+
+        if (timestamp_value &&
+            virFileSetXAttr(dst, timestamp_name, timestamp_value) < 0) {
+            ignore_value(virFileRemoveXAttr(dst, ref_name));
+            ignore_value(virFileRemoveXAttr(dst, attr_name));
+            return -1;
+        }
     }
 
     return 0;
diff --git a/tests/qemusecuritymock.c b/tests/qemusecuritymock.c
index a15eef29c9..373d64305a 100644
--- a/tests/qemusecuritymock.c
+++ b/tests/qemusecuritymock.c
@@ -32,6 +32,7 @@
 #include "viralloc.h"
 #include "qemusecuritytest.h"
 #include "security/security_manager.h"
+#include "virhostuptime.h"
 
 #define VIR_FROM_THIS VIR_FROM_NONE
 
@@ -488,3 +489,14 @@ virProcessRunInFork(virProcessForkCallback cb,
 {
     return cb(-1, opaque);
 }
+
+
+/* We don't really need to mock this function. The qemusecuritytest doesn't
+ * care about the actual value. However, travis runs build and tests in a
+ * container where utmp is missing and thus this function fails. */
+int
+virHostGetBootTime(unsigned long long *when)
+{
+    *when = 1234567890;
+    return 0;
+}
-- 
2.21.0

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On Wed, Aug 14, 2019 at 16:33:23 +0200, Michal Privoznik wrote:
> It may happen that we leave some XATTRs behind. For instance, on
> a sudden power loss, the host just shuts down without calling
> restore on domain paths. This creates a problem, because when the
> host starts up again, the XATTRs are there but they don't reflect
> the true state and this may result in libvirt denying start of a
> domain.
> 
> To solve this, save a unique timestamp among with our XATTRs. The
> timestamp consists of host UUID + boot timestamp.
> 
> Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
> ---
>  src/security/security_util.c | 202 ++++++++++++++++++++++++++++++++++-
>  tests/qemusecuritymock.c     |  12 +++
>  2 files changed, 213 insertions(+), 1 deletion(-)
> 
> diff --git a/src/security/security_util.c b/src/security/security_util.c
> index 365b2dd2d6..d063f526be 100644
> --- a/src/security/security_util.c
> +++ b/src/security/security_util.c
> @@ -22,11 +22,16 @@
>  #include "virfile.h"
>  #include "virstring.h"
>  #include "virerror.h"
> +#include "virlog.h"
> +#include "viruuid.h"
> +#include "virhostuptime.h"
>  
>  #include "security_util.h"
>  
>  #define VIR_FROM_THIS VIR_FROM_SECURITY
>  
> +VIR_LOG_INIT("security.security_util");
> +
>  /* There are four namespaces available on Linux (xattr(7)):
>   *
>   *  user - can be modified by anybody,
> @@ -83,6 +88,157 @@ virSecurityGetRefCountAttrName(const char *name ATTRIBUTE_UNUSED)
>  }
>  
>  
> +static char *
> +virSecurityGetTimestampAttrName(const char *name ATTRIBUTE_UNUSED)
> +{
> +    char *ret = NULL;
> +#ifdef XATTR_NAMESPACE
> +    ignore_value(virAsprintf(&ret, XATTR_NAMESPACE".libvirt.security.timestamp_%s", name));
> +#else
> +    errno = ENOSYS;
> +    virReportSystemError(errno, "%s",
> +                         _("Extended attributes are not supported on this system"));
> +#endif
> +    return ret;
> +}

Again, put #ifdef outside, please.

> +
> +
> +/* This global timestamp holds combination of host UUID + boot time so that we
> + * can detect stale XATTRs. For instance, on a sudden power loss, XATTRs are
> + * not going to change (nobody will call restoreLabel()) and thus they reflect
> + * state from just before the power loss and if there was a machine running,
> + * then XATTRs there are stale and no one will ever remove them. They don't
> + * reflect the true state (most notably the ref counter).
> + */
> +static char *timestamp;
> +
> +
> +static int
> +virSecurityEnsureTimestamp(void)
> +{
> +    unsigned char uuid[VIR_UUID_BUFLEN] = {0};
> +    char uuidstr[VIR_UUID_STRING_BUFLEN] = {0};
> +    unsigned long long boottime = 0;
> +
> +    if (timestamp)
> +        return 0;
> +
> +    if (virGetHostUUID(uuid) < 0) {
> +        virReportError(VIR_ERR_INTERNAL_ERROR,
> +                       "%s", _("cannot get the host uuid"));
> +        return -1;
> +    }
> +
> +    virUUIDFormat(uuid, uuidstr);
> +
> +    if (virHostGetBootTime(&boottime) < 0) {
> +        virReportSystemError(errno, "%s",
> +                             _("Unable to get host boot time"));
> +        return -1;
> +    }
> +
> +    if (virAsprintf(&timestamp, "%s-%llu", uuidstr, boottime) < 0)
> +        return -1;
> +
> +    return 0;
> +}
> +
> +
> +/**
> + * virSecurityValidateTimestamp:
> + * @name: security driver name
> + * @path: file name
> + *
> + * Check if remembered label on @path for security driver @name
> + * is valid, i.e. the label has been set since the last boot. If
> + * the label was set in previous runs, all XATTRs related to
> + * @name are removed so that clean slate is restored.
> + *
> + * Returns: 0 if remembered label is valid,
> + *          1 if remembered label was not valid,
> + *         -1 otherwise.
> + */
> +static int
> +virSecurityValidateTimestamp(const char *name,
> +                             const char *path)
> +{
> +    VIR_AUTOFREE(char *) timestamp_name = NULL;
> +    VIR_AUTOFREE(char *) value = NULL;
> +
> +    if (virSecurityEnsureTimestamp() < 0)
> +        return -1;
> +
> +    if (!(timestamp_name = virSecurityGetTimestampAttrName(name)))
> +        return -1;
> +
> +    errno = 0;
> +    if (virFileGetXAttrQuiet(path, timestamp_name, &value) < 0) {
> +        if (errno == ENOSYS || errno == ENOTSUP) {
> +            /* XATTRs are not supported. */

Redundant comment.

> +            return -1;
> +        } else if (errno != ENODATA) {
> +            virReportSystemError(errno,
> +                                 _("Unable to get XATTR %s on %s"),
> +                                 timestamp_name,
> +                                 path);
> +            return -1;
> +        }
> +
> +        /* Timestamp is missing. We can continue and claim a valid timestamp.
> +         * But then we would never remove stale XATTRs. Therefore, claim it
> +         * invalid and have the code below remove all XATTRs. This of course
> +         * means that we will not restore the original owner, but the plus side
> +         * is that we reset refcounter which will represent the true state.
> +         */
> +    }
> +
> +    if (STREQ_NULLABLE(value, timestamp)) {
> +        /* Hooray, XATTRs are valid. */

Redundant comment.

> +        VIR_DEBUG("XATTRs on %s secdriver=%s are valid", path, name);
> +        return 0;
> +    }

I believe the reason for having UUID in the timestamp is to be able to
detect when the label was remembered on a different host. But here, you
completely ignore this and always remove the remembered labels when it
was remembered on a different host or after a reboot. And since you will
need to check the UUID separately from the timestamp, I think it would
make sense to store them separately rather than combining them in a
single value.

> +
> +    VIR_WARN("Invalid XATTR timestamp detected on %s secdriver=%s", path, name);
> +
> +    if (virSecurityMoveRememberedLabel(name, path, NULL) < 0)
> +        return -1;
> +
> +    return 1;
> +}

Jirka

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