[PATCH 3.12 49/83] sch_tbf: handle too small burst

Greg Kroah-Hartman
2013-12-06T22:32:19Z

From: Eric Dumazet <edumazet@google.com>

[ Upstream commit 4d0820cf6a55d72350cb2d24a4504f62fbde95d9 ]

If a too small burst is inadvertently set on TBF, we might trigger
a bug in tbf_segment(), as 'skb' instead of 'segs' was used in a
qdisc_reshape_fail() call.

tc qdisc add dev eth0 root handle 1: tbf latency 50ms burst 1KB rate
50mbit

Fix the bug, and add a warning, as such configuration is not
going to work anyway for non GSO packets.

(For some reason, one has to use a burst >= 1520 to get a working
configuration, even with old kernels. This is a probable iproute2/tc
bug)

Based on a report and initial patch from Yang Yingliang

Fixes: e43ac79a4bc6 ("sch_tbf: segment too big GSO packets")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Yang Yingliang <yangyingliang@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/sched/sch_tbf.c | 32 +++++++++++++++++++++++++-------
1 file changed, 25 insertions(+), 7 deletions(-)

--- a/net/sched/sch_tbf.c
+++ b/net/sched/sch_tbf.c
@@ -21,6 +21,7 @@
#include <net/netlink.h>
#include <net/sch_generic.h>
#include <net/pkt_sched.h>
+#include <net/tcp.h>

/* Simple Token Bucket Filter.
@@ -117,6 +118,22 @@ struct tbf_sched_data {
};

+/*
+ * Return length of individual segments of a gso packet,
+ * including all headers (MAC, IP, TCP/UDP)
+ */
+static unsigned int skb_gso_seglen(const struct sk_buff *skb)
+{
+ unsigned int hdr_len = skb_transport_header(skb) - skb_mac_header(skb);
+ const struct skb_shared_info *shinfo = skb_shinfo(skb);
+
+ if (likely(shinfo->gso_type & (SKB_GSO_TCPV4 | SKB_GSO_TCPV6)))
+ hdr_len += tcp_hdrlen(skb);
+ else
+ hdr_len += sizeof(struct udphdr);
+ return hdr_len + shinfo->gso_size;
+}
+
/* GSO packet is too big, segment it so that tbf can transmit
* each segment in time
*/
@@ -136,12 +153,8 @@ static int tbf_segment(struct sk_buff *s
while (segs) {
nskb = segs->next;
segs->next = NULL;
- if (likely(segs->len <= q->max_size)) {
- qdisc_skb_cb(segs)->pkt_len = segs->len;
- ret = qdisc_enqueue(segs, q->qdisc);
- } else {
- ret = qdisc_reshape_fail(skb, sch);
- }
+ qdisc_skb_cb(segs)->pkt_len = segs->len;
+ ret = qdisc_enqueue(segs, q->qdisc);
if (ret != NET_XMIT_SUCCESS) {
if (net_xmit_drop_count(ret))
sch->qstats.drops++;
@@ -163,7 +176,7 @@ static int tbf_enqueue(struct sk_buff *s
int ret;

if (qdisc_pkt_len(skb) > q->max_size) {
- if (skb_is_gso(skb))
+ if (skb_is_gso(skb) && skb_gso_seglen(skb) <= q->max_size)
return tbf_segment(skb, sch);
return qdisc_reshape_fail(skb, sch);
}
@@ -316,6 +329,11 @@ static int tbf_change(struct Qdisc *sch,
if (max_size < 0)
goto done;

+ if (max_size < psched_mtu(qdisc_dev(sch)))
+ pr_warn_ratelimited("sch_tbf: burst %u is lower than device %s mtu (%u) !\n",
+ max_size, qdisc_dev(sch)->name,
+ psched_mtu(qdisc_dev(sch)));
+
if (q->qdisc != &noop_qdisc) {
err = fifo_set_limit(q->qdisc, qopt->limit);
if (err)