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@xxxxxxxxxx>
> ---
> 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(×tamp, "%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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