[PATCH net] net/sched: flower: fix infinite loop in fl_walk()

[Davide Caratti <dcaratti@redhat.com>]

on some CPUs (e.g. i686), tcf_walker.cookie has the same size as the IDR.
In this situation, the following script:

 # tc filter add dev eth0 ingress handle 0xffffffff flower action ok
 # tc filter show dev eth0 ingress

results in an infinite loop. It happened also on other CPUs (e.g x86_64),
before commit 061775583e35 ("net: sched: flower: introduce reference
counting for filters"), because 'handle' + 1 made the u32 overflow before
it was assigned to 'cookie'; but that commit replaced the assignment with
a self-increment of 'cookie', so the problem was indirectly fixed.

Ensure not to call idr_get_next_ul() when 'cookie' contains an overflowed
value, and bail out of fl_walk() when its value is equal to ULONG_MAX.
While at it, add a TDC selftest that can be used to reproduce the problem.

 test results (on 5.2.0-0.rc5.git0.1.fc31.i686)

 unpatched (or affected) kernel:
 # ./tdc.py  -e 2ff3 -d dum0
 Test 2ff3: Add flower with max handle and then dump it
 All test results:
 1..1
 not ok 1 2ff3 - Add flower with max handle and then dump it
         Could not match regex pattern. Verify command output:
 Command "/sbin/tc filter show dev dum0 ingress" timed out

 patched (or unaffected) kernel:
 # ./tdc.py  -e 2ff3 -d dum0
 Test 2ff3: Add flower with max handle and then dump it
 All test results:
 1..1
 ok 1 2ff3 - Add flower with max handle and then dump it

Fixes: 01683a146999 ("net: sched: refactor flower walk to iterate over idr")
Reported-by: Li Shuang <shuali@redhat.com>
Signed-off-by: Davide Caratti <dcaratti@redhat.com>
---
 net/sched/cls_flower.c                        |  2 ++
 .../tc-testing/tc-tests/filters/tests.json    | 19 +++++++++++++++++++
 2 files changed, 21 insertions(+)

diff --git a/net/sched/cls_flower.c b/net/sched/cls_flower.c
index eedd5786c084..acc86ae159f4 100644
--- a/net/sched/cls_flower.c
+++ b/net/sched/cls_flower.c
@@ -1702,6 +1702,8 @@ static void fl_walk(struct tcf_proto *tp, struct tcf_walker *arg,
 			break;
 		}
 		__fl_put(f);
+		if (arg->cookie == ULONG_MAX)
+			break;
 		arg->cookie++;
 		arg->count++;
 	}
diff --git a/tools/testing/selftests/tc-testing/tc-tests/filters/tests.json b/tools/testing/selftests/tc-testing/tc-tests/filters/tests.json
index e2f92cefb8d5..16559c436f21 100644
--- a/tools/testing/selftests/tc-testing/tc-tests/filters/tests.json
+++ b/tools/testing/selftests/tc-testing/tc-tests/filters/tests.json
@@ -38,6 +38,25 @@
             "$TC qdisc del dev $DEV1 clsact"
         ]
     },
+    {
+        "id": "2ff3",
+        "name": "Add flower with max handle and then dump it",
+        "category": [
+            "filter",
+            "flower"
+        ],
+        "setup": [
+            "$TC qdisc add dev $DEV2 ingress"
+        ],
+        "cmdUnderTest": "$TC filter add dev $DEV2 protocol ip pref 1 parent ffff: handle 0xffffffff flower action ok",
+        "expExitCode": "0",
+        "verifyCmd": "$TC filter show dev $DEV2 ingress",
+        "matchPattern": "filter protocol ip pref 1 flower.*handle 0xffffffff",
+        "matchCount": "1",
+        "teardown": [
+            "$TC qdisc del dev $DEV2 ingress"
+        ]
+    },
     {
         "id": "d052",
         "name": "Add 1M filters with the same action",
-- 
2.20.1