4.18-stable review patch. If anyone has any objections, please let me know.
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From: Al Viro viro@zeniv.linux.org.uk
[ Upstream commit 6d4c407744dd0338da5d5d76f40dce5adabfb30a ]
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).
Reproducer:
tc qdisc add dev eth0 ingress tc filter add dev eth0 parent ffff: protocol ip prio 100 handle 1: \ u32 divisor 1 tc filter add dev eth0 parent ffff: protocol ip prio 200 handle 2: \ u32 divisor 1 tc filter add dev eth0 parent ffff: protocol ip prio 100 \ handle 1:0:11 u32 ht 1: link 801: offset at 0 mask 0f00 shift 6 \ plus 0 eat match ip protocol 6 ff tc filter delete dev eth0 parent ffff: protocol ip prio 200 tc filter change dev eth0 parent ffff: protocol ip prio 100 \ handle 1:0:11 u32 ht 1: link 0: offset at 0 mask 0f00 shift 6 plus 0 \ eat match ip protocol 6 ff tc filter delete dev eth0 parent ffff: protocol ip prio 100
Signed-off-by: Al Viro viro@zeniv.linux.org.uk Signed-off-by: Jamal Hadi Salim jhs@mojatatu.com Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- net/sched/cls_u32.c | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-)
--- a/net/sched/cls_u32.c +++ b/net/sched/cls_u32.c @@ -397,6 +397,7 @@ 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; @@ -608,7 +609,7 @@ static int u32_destroy_hnode(struct tcf_ 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);
@@ -647,7 +648,7 @@ static void u32_destroy(struct tcf_proto
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) { @@ -696,7 +697,6 @@ static int u32_delete(struct tcf_proto * }
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"); @@ -706,11 +706,11 @@ static int u32_delete(struct tcf_proto * out: *last = true; if (root_ht) { - if (root_ht->refcnt > 1) { + if (root_ht->refcnt > 2) { *last = false; goto ret; } - if (root_ht->refcnt == 1) { + if (root_ht->refcnt == 2) { if (!ht_empty(root_ht)) { *last = false; goto ret;