[PATCH] net: sched: sch: Bounds check priority

[Kees Cook]

Nothing was explicitly bounds checking the priority index used to access
clpriop[]. WARN and bail out early if it's pathological. Seen with GCC 13:

../net/sched/sch_htb.c: In function 'htb_activate_prios':
../net/sched/sch_htb.c:437:44: warning: array subscript [0, 31] is outside array bounds of 'struct htb_prio[8]' [-Warray-bounds=]
  437 |                         if (p->inner.clprio[prio].feed.rb_node)
      |                             ~~~~~~~~~~~~~~~^~~~~~
../net/sched/sch_htb.c:131:41: note: while referencing 'clprio'
  131 |                         struct htb_prio clprio[TC_HTB_NUMPRIO];
      |                                         ^~~~~~

Cc: Jamal Hadi Salim <jhs@xxxxxxxxxxxx>
Cc: Cong Wang <xiyou.wangcong@xxxxxxxxx>
Cc: Jiri Pirko <jiri@xxxxxxxxxxx>
Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
Cc: Eric Dumazet <edumazet@xxxxxxxxxx>
Cc: Jakub Kicinski <kuba@xxxxxxxxxx>
Cc: Paolo Abeni <pabeni@xxxxxxxxxx>
Cc: netdev@xxxxxxxxxxxxxxx
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
 net/sched/sch_htb.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/net/sched/sch_htb.c b/net/sched/sch_htb.c
index f46643850df8..cc28e41fb745 100644
--- a/net/sched/sch_htb.c
+++ b/net/sched/sch_htb.c
@@ -431,7 +431,10 @@ static void htb_activate_prios(struct htb_sched *q, struct htb_class *cl)
 	while (cl->cmode == HTB_MAY_BORROW && p && mask) {
 		m = mask;
 		while (m) {
-			int prio = ffz(~m);
+			unsigned int prio = ffz(~m);
+
+			if (WARN_ON_ONCE(prio > ARRAY_SIZE(p->inner.clprio)))
+				break;
 			m &= ~(1 << prio);
 
 			if (p->inner.clprio[prio].feed.rb_node)
-- 
2.34.1