On 2018-09-05 3:04 p.m., Al Viro wrote:
From: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
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@xxxxxxxxxxxxxxx
Signed-off-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
For networking patches, subject should be reflective of tree and
subsystem. Example for this one:
"[PATCH net 1/7]:net: sched: cls_u32: fix hnode refcounting"
Also useful to have a cover letter summarizing the patchset
in 0/7. Otherwise
Acked-by: Jamal Hadi Salim <jhs@xxxxxxxxxxxx>
cheers,
jamal
