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Merge branch 'net_sched-hfsc-address-reentrant-enqueue-adding-class-to-eltree-twice'

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Pedro Tammela says:

====================
net_sched: hfsc: Address reentrant enqueue adding class to eltree twice

Savino says:
    "We are writing to report that this recent patch
    (141d34391a)
    can be bypassed, and a UAF can still occur when HFSC is utilized with
    NETEM.

    The patch only checks the cl->cl_nactive field to determine whether
    it is the first insertion or not, but this field is only
    incremented by init_vf.

    By using HFSC_RSC (which uses init_ed), it is possible to bypass the
    check and insert the class twice in the eltree.
    Under normal conditions, this would lead to an infinite loop in
    hfsc_dequeue for the reasons we already explained in this report.

    However, if TBF is added as root qdisc and it is configured with a
    very low rate,
    it can be utilized to prevent packets from being dequeued.
    This behavior can be exploited to perform subsequent insertions in the
    HFSC eltree and cause a UAF."

To fix both the UAF and the infinite loop, with netem as an hfsc child,
check explicitly in hfsc_enqueue whether the class is already in the eltree
whenever the HFSC_RSC flag is set.

Also add a TDC test to reproduce the UAF scenario.
====================

Link: https://patch.msgid.link/20250522181448.1439717-1-pctammela@mojatatu.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
This commit is contained in:
Paolo Abeni
2025-05-28 08:55:37 +02:00
parent 67af4ec948 2945ff733d
commit fc6895345f
2 changed files with 43 additions and 1 deletions
Download Patch File Download Diff File Expand all files Collapse all files

9
net/sched/sch_hfsc.c
View File

@@ -175,6 +175,11 @@ struct hfsc_sched {
#define HT_INFINITY 0xffffffffffffffffULL /* infinite time value */
static bool cl_in_el_or_vttree(struct hfsc_class *cl)
{
return ((cl->cl_flags & HFSC_FSC) && cl->cl_nactive) ||
((cl->cl_flags & HFSC_RSC) && !RB_EMPTY_NODE(&cl->el_node));
}
/*
* eligible tree holds backlogged classes being sorted by their eligible times.
@@ -1040,6 +1045,8 @@ hfsc_change_class(struct Qdisc *sch, u32 classid, u32 parentid,
if (cl == NULL)
return -ENOBUFS;
RB_CLEAR_NODE(&cl->el_node);
err = tcf_block_get(&cl->block, &cl->filter_list, sch, extack);
if (err) {
kfree(cl);
@@ -1572,7 +1579,7 @@ hfsc_enqueue(struct sk_buff *skb, struct Qdisc *sch, struct sk_buff **to_free)
sch->qstats.backlog += len;
sch->q.qlen++;
if (first && !cl->cl_nactive) {
if (first && !cl_in_el_or_vttree(cl)) {
if (cl->cl_flags & HFSC_RSC)
init_ed(cl, len);
if (cl->cl_flags & HFSC_FSC)

35
tools/testing/selftests/tc-testing/tc-tests/infra/qdiscs.json
View File

@@ -600,5 +600,40 @@
"matchPattern": "qdisc hfsc",
"matchCount": "1",
"teardown": ["$TC qdisc del dev $DEV1 root handle 1: drr"]
},
{
"id": "309e",
"name": "Test HFSC eltree double add with reentrant enqueue behaviour on netem",
"category": [
"qdisc",
"hfsc"
],
"plugins": {
"requires": "nsPlugin"
},
"setup": [
"$IP link set dev $DUMMY up || true",
"$IP addr add 10.10.11.10/24 dev $DUMMY || true",
"$TC qdisc add dev $DUMMY root handle 1: tbf rate 8bit burst 100b latency 1s",
"$TC qdisc add dev $DUMMY parent 1:0 handle 2:0 hfsc",
"ping -I $DUMMY -f -c10 -s48 -W0.001 10.10.11.1 || true",
"$TC class add dev $DUMMY parent 2:0 classid 2:1 hfsc rt m2 20Kbit",
"$TC qdisc add dev $DUMMY parent 2:1 handle 3:0 netem duplicate 100%",
"$TC class add dev $DUMMY parent 2:0 classid 2:2 hfsc rt m2 20Kbit",
"$TC filter add dev $DUMMY parent 2:0 protocol ip prio 1 u32 match ip dst 10.10.11.2/32 flowid 2:1",
"$TC filter add dev $DUMMY parent 2:0 protocol ip prio 2 u32 match ip dst 10.10.11.3/32 flowid 2:2",
"ping -c 1 10.10.11.2 -I$DUMMY > /dev/null || true",
"$TC filter del dev $DUMMY parent 2:0 protocol ip prio 1",
"$TC class del dev $DUMMY classid 2:1",
"ping -c 1 10.10.11.3 -I$DUMMY > /dev/null || true"
],
"cmdUnderTest": "$TC class change dev $DUMMY parent 2:0 classid 2:2 hfsc sc m2 20Kbit",
"expExitCode": "0",
"verifyCmd": "$TC -j class ls dev $DUMMY classid 2:1",
"matchJSON": [],
"teardown": [
"$TC qdisc del dev $DUMMY handle 1:0 root",
"$IP addr del 10.10.10.10/24 dev $DUMMY || true"
]
}
]