From: Al Viro viro@zeniv.linux.org.uk
cls_u32.c misuses refcounts for struct tc_u_hnode - it counts references via ->hlist and via ->tp_root together. u32_destroy() drops the former and, in case when there had been links, leaves the sucker on the list. As the result, there's nothing to protect it from getting freed once links are dropped. That also makes the "is it busy" check incapable of catching the root hnode - it *is* busy (there's a reference from tp), but we don't see it as something separate. "Is it our root?" check partially covers that, but the problem exists for others' roots as well.
AFAICS, the minimal fix preserving the existing behaviour (where it doesn't include oopsen, that is) would be this: * count tp->root and tp_c->hlist as separate references. I.e. have u32_init() set refcount to 2, not 1. * in u32_destroy() we always drop the former; in u32_destroy_hnode() - the latter.
That way we have *all* references contributing to refcount. List removal happens in u32_destroy_hnode() (called only when ->refcnt is 1) an in u32_destroy() in case of tc_u_common going away, along with everything reachable from it. IOW, that way we know that u32_destroy_key() won't free something still on the list (or pointed to by someone's ->root).
Cc: stable@vger.kernel.org Signed-off-by: Al Viro viro@zeniv.linux.org.uk --- net/sched/cls_u32.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/net/sched/cls_u32.c b/net/sched/cls_u32.c index f218ccf1e2d9..3f985f29ef30 100644 --- a/net/sched/cls_u32.c +++ b/net/sched/cls_u32.c @@ -398,6 +398,7 @@ static int u32_init(struct tcf_proto *tp) rcu_assign_pointer(tp_c->hlist, root_ht); root_ht->tp_c = tp_c;
+ root_ht->refcnt++; rcu_assign_pointer(tp->root, root_ht); tp->data = tp_c; return 0; @@ -610,7 +611,7 @@ static int u32_destroy_hnode(struct tcf_proto *tp, struct tc_u_hnode *ht, struct tc_u_hnode __rcu **hn; struct tc_u_hnode *phn;
- WARN_ON(ht->refcnt); + WARN_ON(--ht->refcnt);
u32_clear_hnode(tp, ht, extack);
@@ -649,7 +650,7 @@ static void u32_destroy(struct tcf_proto *tp, struct netlink_ext_ack *extack)
WARN_ON(root_ht == NULL);
- if (root_ht && --root_ht->refcnt == 0) + if (root_ht && --root_ht->refcnt == 1) u32_destroy_hnode(tp, root_ht, extack);
if (--tp_c->refcnt == 0) { @@ -698,7 +699,6 @@ static int u32_delete(struct tcf_proto *tp, void *arg, bool *last, }
if (ht->refcnt == 1) { - ht->refcnt--; u32_destroy_hnode(tp, ht, extack); } else { NL_SET_ERR_MSG_MOD(extack, "Can not delete in-use filter");