commit 7041101ff6c3073fd8f2e99920f535b111c929cb upstream.

if sch_fq is configured with "initial quantum" having values greater than INT_MAX, the first assignment of "credit" does signed integer overflow to a very negative value. In this situation, the syzkaller script provided by Cristoph triggers the CPU soft-lockup warning even with few sockets. It's not an infinite loop, but "credit" wasn't probably meant to be minus 2Gb for each new flow. Capping "initial quantum" to INT_MAX proved to fix the issue.

This patch doesn't use netlink validation helpers, since they might not be available on all stable branches.

Reported-by: Christoph Paasch cpaasch@apple.com Link: https://github.com/multipath-tcp/mptcp_net-next/issues/377 Fixes: afe4fd062416 ("pkt_sched: fq: Fair Queue packet scheduler") Cc: stable@vger.kernel.org Reviewed-by: Eric Dumazet edumazet@google.com Signed-off-by: Davide Caratti dcaratti@redhat.com --- net/sched/sch_fq.c | 12 ++++++++++-- 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/net/sched/sch_fq.c b/net/sched/sch_fq.c index 48d14fb90ba0..12efbcfc2938 100644 --- a/net/sched/sch_fq.c +++ b/net/sched/sch_fq.c @@ -842,8 +842,16 @@ static int fq_change(struct Qdisc *sch, struct nlattr *opt, } }

- if (tb[TCA_FQ_INITIAL_QUANTUM]) - q->initial_quantum = nla_get_u32(tb[TCA_FQ_INITIAL_QUANTUM]); + if (tb[TCA_FQ_INITIAL_QUANTUM]) { + u32 initial_quantum = nla_get_u32(tb[TCA_FQ_INITIAL_QUANTUM]); + + if (initial_quantum <= INT_MAX) { + q->initial_quantum = initial_quantum; + } else { + NL_SET_ERR_MSG_MOD(extack, "invalid initial quantum"); + err = -EINVAL; + } + }

if (tb[TCA_FQ_FLOW_DEFAULT_RATE]) pr_warn_ratelimited("sch_fq: defrate %u ignored.\n",