From 66ab4c59b74db7ab53a1c9083feaaede393a96a0 Mon Sep 17 00:00:00 2001 From: Jamal Hadi Salim Date: Wed, 2 Sep 2026 17:29:08 -0400 Subject: [PATCH 1/3] net: cap tx_queue_len at S16_MAX to prevent oversized ring allocations Several subsystems allocate ring buffers sized by dev->tx_queue_len with no upper bound. An unprivileged user (via unshare -Urn) can set a huge tx_queue_len and exhaust global memory with ring allocations: - pfifo_fast: pfifo_fast_init() and pfifo_fast_change_tx_queue_len() allocate 3 skb_array rings of tx_queue_len entries each. - tun: tun_queue_resize() and the queue-attach path resize ptr_rings to tx_queue_len on the NETDEV_CHANGE_TX_QUEUE_LEN notifier. - tap (macvtap/ipvtap): tap_queue_resize() and tap_init() resize/init ptr_rings to tx_queue_len on the same notifier. netif_change_tx_queue_len() is the single entry point for IFLA_TXQLEN, sysfs, and the SIOCSIFTXQLEN ioctl. Cap new_len at S16_MAX (32767) there so the oversized value is rejected at set time. This takes effect whether the device is up or down, before dev->tx_queue_len is written, before any notifier fires, and before any ring is allocated. The "> S16_MAX" check also subsumes the previous unsigned-long truncation test, and a negative ifr_qlen from the ioctl lands far above the cap after conversion, so both old failure modes are covered by the one comparison. tx_queue_len is ambigious: both a per-ring sizing multiplier and a default queue-length/limit knob for consumers that allocate nothing at set time (pfifo/bfifo/gred/plug/sfb limits, htb direct_qlen, qfq max_classes, teql). 32767 is chosen as the largest value NLA_POLICY_FULL_RANGE can express for the u32 IFLA_TXQLEN policy in patch 2/3 while staying a legitimate queue length on high-BDP paths; the ring-memory trade-off of a shared knob is disclosed below. Conditions to recreate the bug: - CONFIG_NET_SCHED=y, CONFIG_VETH=y, CONFIG_USER_NS=y, CONFIG_NET_NS=y. - Unprivileged user in a fresh user+net namespace (unshare -Urn). - pfifo_fast: create veth pairs, set tx_queue_len to 500000, attach mq+pfifo_fast. ~28 iterations OOMs a 2GB guest. - tun: create 50 tun devices with IFF_MULTI_QUEUE, set tx_queue_len to 500000, open 8 queues each. ~1.6GB of ptr_ring allocations OOMs a 512MB guest. - tap: same as tun with IFF_TAP. ~960MB OOMs a 512MB guest. - On the fixed kernel the oversized tx_queue_len is rejected with -ERANGE at set time (all four paths: RTM_SETLINK, RTM_NEWLINK create, sysfs, ioctl - the latter two via this check, the former two via this check and the 2/3 parse policy respectively). Fixes: 6a643ddb5624 ("net: introduce helper dev_change_tx_queue_len()") Reported-by: Vega Closes: https://lore.kernel.org/netdev/20260828121902.66837-1-jhs@mojatatu.com/ Tested-by: Victor Nogueira Signed-off-by: Jamal Hadi Salim Link: https://patch.msgid.link/QDISC-2899.v2.20260901233641@mojatatu.com Signed-off-by: Jakub Kicinski --- net/core/dev.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/net/core/dev.c b/net/core/dev.c index 290e0f099e6b..ecfbd72d5d1a 100644 --- a/net/core/dev.c +++ b/net/core/dev.c @@ -9982,7 +9982,7 @@ int netif_change_tx_queue_len(struct net_device *dev, unsigned long new_len) unsigned int orig_len = dev->tx_queue_len; int res; - if (new_len != (unsigned int)new_len) + if (new_len > S16_MAX) return -ERANGE; if (new_len != orig_len) { From 1aa9e143bf51405665a793d4cc925e1c4f0c5922 Mon Sep 17 00:00:00 2001 From: Jamal Hadi Salim Date: Wed, 2 Sep 2026 17:29:09 -0400 Subject: [PATCH 2/3] net: reject oversized tx_queue_len at netlink parse time rtnl_create_link() assigns IFLA_TXQLEN directly to dev->tx_queue_len without going through netif_change_tx_queue_len(), so a device created with "ip link add ... txqueuelen 500000" bypasses the S16_MAX cap and still triggers the oversized ring allocations in pfifo_fast, tun and tap. The veth peer nest (rtnl_nla_parse_ifinfomsg()) and the RTM_NEWLINK-on-existing-device path reach the same sinks. Enforce the cap in ifla_policy instead: IFLA_TXQLEN becomes NLA_POLICY_FULL_RANGE(NLA_U32, &txqlen_range) with txqlen_range = { .min = 0, .max = S16_MAX }. All netlink consumers parse against this policy - rtnl_setlink(), rtnl_newlink() (create and change), and the veth peer nest - so every netlink path is capped at parse time and rejects the attribute with -ERANGE plus a proper "integer out of range" extack message before any device state is modified (the RTM_SETLINK half-application wart is gone with it). Document the bound in the rt-link.yaml netlink spec. Conditions to recreate the bug: - CONFIG_NET_SCHED=y, CONFIG_VETH=y, CONFIG_USER_NS=y, CONFIG_NET_NS=y. - Unprivileged user in a fresh user+net namespace (unshare -Urn): ip link add v0 txqueuelen 500000 type veth peer name v1 -> on the fixed kernel this is rejected with -ERANGE ("integer out of range" extack) instead of installing an oversized tx_queue_len that later inflates pfifo_fast/tun/tap ring allocations. - ip link set v0 txqueuelen 500000 is likewise rejected at parse time. Fixes: 38f7b870d4a6 ("[RTNETLINK]: Link creation API") Reported-by: Vega Tested-by: Victor Nogueira Signed-off-by: Jamal Hadi Salim Link: https://patch.msgid.link/QDISC-2899.v2.20260901233641@mojatatu.com.2 Signed-off-by: Jakub Kicinski --- Documentation/netlink/specs/rt-link.yaml | 2 ++ net/core/rtnetlink.c | 7 ++++++- 2 files changed, 8 insertions(+), 1 deletion(-) diff --git a/Documentation/netlink/specs/rt-link.yaml b/Documentation/netlink/specs/rt-link.yaml index b80c2ac3ac31..99f6fba456cc 100644 --- a/Documentation/netlink/specs/rt-link.yaml +++ b/Documentation/netlink/specs/rt-link.yaml @@ -898,6 +898,8 @@ attribute-sets: - name: txqlen type: u32 + checks: + max: 32767 - name: map type: binary diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c index 81c5a6104dea..be9d1625bac3 100644 --- a/net/core/rtnetlink.c +++ b/net/core/rtnetlink.c @@ -2287,6 +2287,11 @@ static int rtnl_fill_ifinfo(struct sk_buff *skb, return -EMSGSIZE; } +static const struct netlink_range_validation txqlen_range = { + .min = 0, + .max = S16_MAX, +}; + static const struct nla_policy ifla_policy[IFLA_MAX+1] = { [IFLA_UNSPEC] = { .strict_start_type = IFLA_DPLL_PIN }, [IFLA_IFNAME] = { .type = NLA_STRING, .len = IFNAMSIZ-1 }, @@ -2297,7 +2302,7 @@ static const struct nla_policy ifla_policy[IFLA_MAX+1] = { [IFLA_LINK] = { .type = NLA_U32 }, [IFLA_MASTER] = { .type = NLA_U32 }, [IFLA_CARRIER] = { .type = NLA_U8 }, - [IFLA_TXQLEN] = { .type = NLA_U32 }, + [IFLA_TXQLEN] = NLA_POLICY_FULL_RANGE(NLA_U32, &txqlen_range), [IFLA_WEIGHT] = { .type = NLA_U32 }, [IFLA_OPERSTATE] = { .type = NLA_U8 }, [IFLA_LINKMODE] = { .type = NLA_U8 }, From 0a7252d7f85478080385de4c1072085e30849fe3 Mon Sep 17 00:00:00 2001 From: Jamal Hadi Salim Date: Wed, 2 Sep 2026 17:29:10 -0400 Subject: [PATCH 3/3] selftests: tc-testing: add tx_queue_len cap regression tests Add nine test cases for the S16_MAX tx_queue_len cap to the pfifo_fast suite. Netlink cases exercise the ifla_policy bound (2/3); the two new sysfs cases exercise the netif_change_tx_queue_len() choke point that 1/3 owns (SIOCSIFTXQLEN shares it; the ioctl is not portably reachable from tdc): - dbe3: set txqueuelen 32767 (S16_MAX) - accepted, pins the exact boundary value. - b50e: set txqueuelen 32768 - rejected with -ERANGE. - 40f8: write 32768 to /sys/class/net/*/tx_queue_len - rejected (covers patch 1/3 directly; netlink cannot reach this path). - 4b6e: write 32767 via sysfs - accepted, boundary positive control for the patch-1 path. - b90d: create a dummy with txqueuelen 32767 - accepted. - 57ab: create a dummy with txqueuelen 32768 - rejected at netlink parse time. - e777: create a dummy with txqueuelen 500000 - rejected (the v1 bypass path flagged by review). - 31ac: create a veth with an oversized txqueuelen on the peer nest - rejected (the peer nest is parsed against ifla_policy too). - b567: create a veth with txqueuelen on both ends within the cap - accepted (positive control for the peer nest). The three negative-creation verifies assert device absence ("ip -o link show" must not contain the device), not merely absence of a qlen pattern - the device does not exist when creation fails, so the exit code carries the signal and the verify adds content. The v1 04b5 "resize rollback" case is dropped: with the cap checked first, netif_change_tx_queue_len() returns -ERANGE before the write, the notifier or any qdisc resize, so the case exercised no resize and no rollback. It was also nondeterministic: pre-patch, the resize issues three ~11 MB kvmallocs for qlen 500000 which normally succeed, so the case passed on an unfixed kernel only under memory pressure - its outcome depended on the test host's free memory. Test commands run inside the netns, but nsPlugin creates the veth peer in the root namespace, so the teardown deletes the in-ns end only; deleting the peer via the pair is implicit. Note: iproute2 treats "txqueuelen" appearing after "type X" as a link-type attribute and silently drops it, so the creation cases place it before "type" to actually reach the kernel. Signed-off-by: Jamal Hadi Salim Link: https://patch.msgid.link/QDISC-2899.v2.20260901233641@mojatatu.com.3 Signed-off-by: Jakub Kicinski --- .../tc-tests/qdiscs/pfifo_fast.json | 204 ++++++++++++++++++ 1 file changed, 204 insertions(+) diff --git a/tools/testing/selftests/tc-testing/tc-tests/qdiscs/pfifo_fast.json b/tools/testing/selftests/tc-testing/tc-tests/qdiscs/pfifo_fast.json index 30da27fe8806..a6e25e76ecb1 100644 --- a/tools/testing/selftests/tc-testing/tc-tests/qdiscs/pfifo_fast.json +++ b/tools/testing/selftests/tc-testing/tc-tests/qdiscs/pfifo_fast.json @@ -105,5 +105,209 @@ "teardown": [ "$TC qdisc del dev $DUMMY handle 1: root" ] + }, + { + "id": "dbe3", + "name": "Set tx_queue_len to S16_MAX boundary (32767 accepted)", + "category": [ + "qdisc", + "pfifo_fast" + ], + "plugins": { + "requires": "nsPlugin" + }, + "setup": [], + "cmdUnderTest": "$IP link set dev $DUMMY txqueuelen 32767", + "expExitCode": "0", + "verifyCmd": "$IP link show dev $DUMMY", + "matchPattern": "qlen 32767$", + "matchCount": "1", + "teardown": [] + }, + { + "id": "b50e", + "name": "Reject tx_queue_len above S16_MAX at set time (32768)", + "category": [ + "qdisc", + "pfifo_fast" + ], + "plugins": { + "requires": "nsPlugin" + }, + "setup": [], + "cmdUnderTest": "$IP link set dev $DUMMY txqueuelen 32768", + "expExitCode": "2", + "verifyCmd": "$IP link show dev $DUMMY", + "matchPattern": "qlen 1000$", + "matchCount": "1", + "teardown": [] + }, + { + "id": "40f8", + "name": "Reject tx_queue_len above S16_MAX via sysfs (32768)", + "category": [ + "qdisc", + "pfifo_fast" + ], + "plugins": { + "requires": "nsPlugin" + }, + "setup": [], + "cmdUnderTest": "sh -c 'echo 32768 > /sys/class/net/$DUMMY/tx_queue_len'", + "expExitCode": "1", + "verifyCmd": "$IP link show dev $DUMMY", + "matchPattern": "qlen 1000$", + "matchCount": "1", + "teardown": [] + }, + { + "id": "4b6e", + "name": "Set tx_queue_len to S16_MAX via sysfs (32767 accepted)", + "category": [ + "qdisc", + "pfifo_fast" + ], + "plugins": { + "requires": "nsPlugin" + }, + "setup": [], + "cmdUnderTest": "sh -c 'echo 32767 > /sys/class/net/$DUMMY/tx_queue_len'", + "expExitCode": "0", + "verifyCmd": "$IP link show dev $DUMMY", + "matchPattern": "qlen 32767$", + "matchCount": "1", + "teardown": [] + }, + { + "id": "b90d", + "name": "Create device with tx_queue_len at S16_MAX boundary (32767 accepted)", + "category": [ + "qdisc", + "pfifo_fast" + ], + "plugins": { + "requires": "nsPlugin" + }, + "setup": [ + [ + "$IP link del dev $DUMMY", + 0, + 1 + ] + ], + "cmdUnderTest": "$IP link add dev $DUMMY txqueuelen 32767 type dummy", + "expExitCode": "0", + "verifyCmd": "$IP link show dev $DUMMY", + "matchPattern": "qlen 32767$", + "matchCount": "1", + "teardown": [ + [ + "$IP link del dev $DUMMY", + 0, + 1 + ] + ] + }, + { + "id": "57ab", + "name": "Reject creating device with tx_queue_len above S16_MAX (32768)", + "category": [ + "qdisc", + "pfifo_fast" + ], + "plugins": { + "requires": "nsPlugin" + }, + "setup": [ + [ + "$IP link del dev $DUMMY", + 0, + 1 + ] + ], + "cmdUnderTest": "$IP link add dev $DUMMY txqueuelen 32768 type dummy", + "expExitCode": "2", + "verifyCmd": "$IP -o link show", + "matchPattern": "^[0-9]+: $DUMMY", + "matchCount": "0", + "teardown": [] + }, + { + "id": "e777", + "name": "Reject creating device with oversized tx_queue_len (500000)", + "category": [ + "qdisc", + "pfifo_fast" + ], + "plugins": { + "requires": "nsPlugin" + }, + "setup": [ + [ + "$IP link del dev $DUMMY", + 0, + 1 + ] + ], + "cmdUnderTest": "$IP link add dev $DUMMY txqueuelen 500000 type dummy", + "expExitCode": "2", + "verifyCmd": "$IP -o link show", + "matchPattern": "^[0-9]+: $DUMMY", + "matchCount": "0", + "teardown": [] + }, + { + "id": "31ac", + "name": "Reject veth peer nest tx_queue_len above S16_MAX at create", + "category": [ + "qdisc", + "pfifo_fast" + ], + "plugins": { + "requires": "nsPlugin" + }, + "setup": [ + [ + "$IP link del dev $DEV1", + 0, + 1 + ] + ], + "cmdUnderTest": "$IP link add dev $DEV1 type veth peer name $DEV0 txqueuelen 500000", + "expExitCode": "2", + "verifyCmd": "$IP -o link show", + "matchPattern": "^[0-9]+: $DEV1", + "matchCount": "0", + "teardown": [] + }, + { + "id": "b567", + "name": "Accept veth peer nest tx_queue_len within S16_MAX", + "category": [ + "qdisc", + "pfifo_fast" + ], + "plugins": { + "requires": "nsPlugin" + }, + "setup": [ + [ + "$IP link del dev $DEV1", + 0, + 1 + ] + ], + "cmdUnderTest": "$IP link add dev $DEV1 txqueuelen 100 type veth peer name $DEV0 txqueuelen 200", + "expExitCode": "0", + "verifyCmd": "$IP link show", + "matchPattern": "qlen (100|200)$", + "matchCount": "2", + "teardown": [ + [ + "$IP link del dev $DEV0", + 0, + 1 + ] + ] } ]