net_sched: cls_flow: validate TCA_FLOW_RSHIFT attribute

syzbot found that TCA_FLOW_RSHIFT attribute was not validated. Right shitfing a 32bit integer is undefined for large shift values.

UBSAN: shift-out-of-bounds in net/sched/cls_flow.c:329:23
shift exponent 9445 is too large for 32-bit type 'u32' (aka 'unsigned int')
CPU: 1 UID: 0 PID: 54 Comm: kworker/u8:3 Not tainted 6.13.0-rc3-syzkaller-00180-g4f619d518db9 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/13/2024
Workqueue: ipv6_addrconf addrconf_dad_work
Call Trace:
 <TASK>
  __dump_stack lib/dump_stack.c:94 [inline]
  dump_stack_lvl+0x241/0x360 lib/dump_stack.c:120
  ubsan_epilogue lib/ubsan.c:231 [inline]
  __ubsan_handle_shift_out_of_bounds+0x3c8/0x420 lib/ubsan.c:468
  flow_classify+0x24d5/0x25b0 net/sched/cls_flow.c:329
  tc_classify include/net/tc_wrapper.h:197 [inline]
  __tcf_classify net/sched/cls_api.c:1771 [inline]
  tcf_classify+0x420/0x1160 net/sched/cls_api.c:1867
  sfb_classify net/sched/sch_sfb.c:260 [inline]
  sfb_enqueue+0x3ad/0x18b0 net/sched/sch_sfb.c:318
  dev_qdisc_enqueue+0x4b/0x290 net/core/dev.c:3793
  __dev_xmit_skb net/core/dev.c:3889 [inline]
  __dev_queue_xmit+0xf0e/0x3f50 net/core/dev.c:4400
  dev_queue_xmit include/linux/netdevice.h:3168 [inline]
  neigh_hh_output include/net/neighbour.h:523 [inline]
  neigh_output include/net/neighbour.h:537 [inline]
  ip_finish_output2+0xd41/0x1390 net/ipv4/ip_output.c:236
  iptunnel_xmit+0x55d/0x9b0 net/ipv4/ip_tunnel_core.c:82
  udp_tunnel_xmit_skb+0x262/0x3b0 net/ipv4/udp_tunnel_core.c:173
  geneve_xmit_skb drivers/net/geneve.c:916 [inline]
  geneve_xmit+0x21dc/0x2d00 drivers/net/geneve.c:1039
  __netdev_start_xmit include/linux/netdevice.h:5002 [inline]
  netdev_start_xmit include/linux/netdevice.h:5011 [inline]
  xmit_one net/core/dev.c:3590 [inline]
  dev_hard_start_xmit+0x27a/0x7d0 net/core/dev.c:3606
  __dev_queue_xmit+0x1b73/0x3f50 net/core/dev.c:4434

---
 net/sched/cls_flow.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

index 5502998aace74157320efed71faf40afd196fac4..5c2580a07530e4e0615a7df7ff9d0a35ae9e94b4 100644
@@ -356,7 +356,8 @@ static const struct nla_policy flow_policy[TCA_FLOW_MAX + 1] = {
 	[TCA_FLOW_KEYS]		= { .type = NLA_U32 },
 	[TCA_FLOW_MODE]		= { .type = NLA_U32 },
 	[TCA_FLOW_BASECLASS]	= { .type = NLA_U32 },
-	[TCA_FLOW_RSHIFT]	= { .type = NLA_U32 },
+	[TCA_FLOW_RSHIFT]	= NLA_POLICY_MAX(NLA_U32,
+						 31 /* BITS_PER_U32 - 1 */),
 	[TCA_FLOW_ADDEND]	= { .type = NLA_U32 },
 	[TCA_FLOW_MASK]		= { .type = NLA_U32 },
 	[TCA_FLOW_XOR]		= { .type = NLA_U32 },

2.47.1.613.gc27f4b7a9f-goog

After previous change rshift >= 32 is no longer allowed. Modify the test to use 31, the test doesn't seem to send any traffic so the exact value shouldn't matter.

---
CC: [email protected]
CC: [email protected]
CC: [email protected]
CC: [email protected]
CC: [email protected]
CC: [email protected]

---
 tools/testing/selftests/tc-testing/tc-tests/filters/flow.json | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

index 996448afe31b..91d120548bf5 100644
@@ -78,10 +78,10 @@
         "setup": [
             "$TC qdisc add dev $DEV1 ingress"
         ],
-        "cmdUnderTest": "$TC filter add dev $DEV1 parent ffff: handle 1 prio 1 protocol ip flow map key dst rshift 0xff",
+        "cmdUnderTest": "$TC filter add dev $DEV1 parent ffff: handle 1 prio 1 protocol ip flow map key dst rshift 0x1f",
         "expExitCode": "0",
         "verifyCmd": "$TC filter get dev $DEV1 parent ffff: handle 1 protocol ip prio 1 flow",
-        "matchPattern": "filter parent ffff: protocol ip pref 1 flow chain [0-9]+ handle 0x1 map keys dst rshift 255 baseclass",
+        "matchPattern": "filter parent ffff: protocol ip pref 1 flow chain [0-9]+ handle 0x1 map keys dst rshift 31 baseclass",
         "matchCount": "1",
         "teardown": [
             "$TC qdisc del dev $DEV1 ingress"

2.47.1

Thanks !