On 2026-02-18 14:08, Daniel P. Smith wrote:
When using XSM Flask, passing DOMID_INVALID will result in a NULL pointer
reference from the passing of NULL as the target domain to
xsm_get_domain_state(). Simply not invoking xsm_get_domain_state() when the
target domain is NULL opens the opportunity to circumvent the XSM
get_domain_state access check. This is due to the fact that the call to
xsm_domctl() for get_domain_state op is a no-op check, deferring to
xsm_get_domain_state().
Modify the helper get_domain_state() to ensure the requesting domain has
get_domain_state access for the target domain, whether the target domain is
explicitly set or implicitly determined with a domain state search. In the case
of access not being allowed for a domain found during an implicit search, the
search will continue to the next domain whose state has changed.
Fixes: 3ad3df1bd0aa ("xen: add new domctl get_domain_state")
Reported-by: Chris Rogers <[email protected]>
Reported-by: Dmytro Firsov <[email protected]>
Signed-off-by: Daniel P. Smith <[email protected]>
---
Changes in v2:
- fix commit message
- init dom as -1
- rework loop logic to use test_and_clear_bit()
---
xen/common/domain.c | 27 +++++++++++++++++++++------
xen/common/domctl.c | 7 ++-----
2 files changed, 23 insertions(+), 11 deletions(-)
diff --git a/xen/common/domain.c b/xen/common/domain.c
index de6fdf59236e..2ffec331a8d1 100644
--- a/xen/common/domain.c
+++ b/xen/common/domain.c
@@ -210,7 +210,7 @@ static void set_domain_state_info(struct
xen_domctl_get_domain_state *info,
int get_domain_state(struct xen_domctl_get_domain_state *info, struct domain
*d,
domid_t *domid)
{
- unsigned int dom;
+ unsigned int dom = -1;
int rc = -ENOENT;
struct domain *hdl;
@@ -219,6 +219,10 @@ int get_domain_state(struct xen_domctl_get_domain_state *info, struct domain *d,
if ( d )
{
+ rc = xsm_get_domain_state(XSM_XS_PRIV, d);
+ if ( rc )
+ return rc;
+
set_domain_state_info(info, d);
return 0;
@@ -238,28 +242,39 @@ int get_domain_state(struct xen_domctl_get_domain_state
*info, struct domain *d,
Between the two hunks is this:
hdl = lock_dom_exc_handler();
/*
* Only domain registered for VIRQ_DOM_EXC event is allowed to query
* domains having changed state.
*/
if ( current->domain != hdl )
{
rc = -EACCES;
goto out;
}
So it is only the domain with VIRQ_DOM_EXC that can enter the while loop:
while ( dom_state_changed )
{
- dom = find_first_bit(dom_state_changed, DOMID_MASK + 1);
+ dom = find_next_bit(dom_state_changed, DOMID_MASK + 1, dom + 1);
if ( dom >= DOMID_FIRST_RESERVED )
break;
+
+ d = rcu_lock_domain_by_id(dom);
+ if ( d && xsm_get_domain_state(XSM_XS_PRIV, d) )
... if the VIRQ_DOM_EXC owner is denied for domain d ...
+ {
+ rcu_unlock_domain(d);
+ d = NULL;
+ continue;
... the caller would continue ...
+ }
+
if ( test_and_clear_bit(dom, dom_state_changed) )
... and this bit would never be cleared. Should the VIRQ_DOM_EXC owner
always get to clear the bit even if it cannot see the result? Is this
too much of a corner case to care about?
The patch generally seems okay aside from this.
{
*domid = dom;
- d = rcu_lock_domain_by_id(dom);
-
if ( d )
{
set_domain_state_info(info, d);
-
rcu_unlock_domain(d);
}
else
memset(info, 0, sizeof(*info));
rc = 0;
-
break;
}
+
+ if ( d )
+ {
+ rcu_unlock_domain(d);
+ d = NULL;
+ }
}
out:
diff --git a/xen/common/domctl.c b/xen/common/domctl.c
index 29a7726d32d0..2eedc639c72a 100644
--- a/xen/common/domctl.c
+++ b/xen/common/domctl.c
@@ -860,12 +860,9 @@ long do_domctl(XEN_GUEST_HANDLE_PARAM(xen_domctl_t)
u_domctl)
break;
case XEN_DOMCTL_get_domain_state:
- ret = xsm_get_domain_state(XSM_XS_PRIV, d);
With the initial NULL deref issue, I wondered if this wouldn't be better
off modified to drop the d param - xsm_get_domain_state(XSM_XS_PRIV) -
and changing flask permissions like:
allow dom0_t xen_t:xen get_domain_state;
That would gate the external call, and individual domain permissions
could be checked with xsm_getdomaininfo(), or a new hook if you don't
want to re-use.
But as your approach avoids passing NULL, it seems okay to me. It also
doesn't change the flask policy, which is nice.
Thanks,
Jason
- if ( ret )
- break;
-
- copyback = 1;
ret = get_domain_state(&op->u.get_domain_state, d, &op->domain);
+ if ( !ret )
+ copyback = 1;
break;
default:
