From 551143d8d954fe398324a5caa276f518466c428b Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Thu, 24 Aug 2017 21:12:28 -0700 Subject: [PATCH] net_sched: fix a refcount_t issue with noop_qdisc syzkaller reported a refcount_t warning [1] Issue here is that noop_qdisc refcnt was never really considered as a true refcount, since qdisc_destroy() found TCQ_F_BUILTIN set : if (qdisc->flags & TCQ_F_BUILTIN || !refcount_dec_and_test(&qdisc->refcnt))) return; Meaning that all atomic_inc() we did on noop_qdisc.refcnt were not really needed, but harmless until refcount_t came. To fix this problem, we simply need to not increment noop_qdisc.refcnt, since we never decrement it. [1] refcount_t: increment on 0; use-after-free. ------------[ cut here ]------------ WARNING: CPU: 0 PID: 21754 at lib/refcount.c:152 refcount_inc+0x47/0x50 lib/refcount.c:152 Kernel panic - not syncing: panic_on_warn set ... CPU: 0 PID: 21754 Comm: syz-executor7 Not tainted 4.13.0-rc6+ #20 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 Call Trace: __dump_stack lib/dump_stack.c:16 [inline] dump_stack+0x194/0x257 lib/dump_stack.c:52 panic+0x1e4/0x417 kernel/panic.c:180 __warn+0x1c4/0x1d9 kernel/panic.c:541 report_bug+0x211/0x2d0 lib/bug.c:183 fixup_bug+0x40/0x90 arch/x86/kernel/traps.c:190 do_trap_no_signal arch/x86/kernel/traps.c:224 [inline] do_trap+0x260/0x390 arch/x86/kernel/traps.c:273 do_error_trap+0x120/0x390 arch/x86/kernel/traps.c:310 do_invalid_op+0x1b/0x20 arch/x86/kernel/traps.c:323 invalid_op+0x1e/0x30 arch/x86/entry/entry_64.S:846 RIP: 0010:refcount_inc+0x47/0x50 lib/refcount.c:152 RSP: 0018:ffff8801c43477a0 EFLAGS: 00010282 RAX: 000000000000002b RBX: ffffffff86093c14 RCX: 0000000000000000 RDX: 000000000000002b RSI: ffffffff8159314e RDI: ffffed0038868ee8 RBP: ffff8801c43477a8 R08: 0000000000000001 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000000 R12: ffffffff86093ac0 R13: 0000000000000001 R14: ffff8801d0f3bac0 R15: dffffc0000000000 attach_default_qdiscs net/sched/sch_generic.c:792 [inline] dev_activate+0x7d3/0xaa0 net/sched/sch_generic.c:833 __dev_open+0x227/0x330 net/core/dev.c:1380 __dev_change_flags+0x695/0x990 net/core/dev.c:6726 dev_change_flags+0x88/0x140 net/core/dev.c:6792 dev_ifsioc+0x5a6/0x930 net/core/dev_ioctl.c:256 dev_ioctl+0x2bc/0xf90 net/core/dev_ioctl.c:554 sock_do_ioctl+0x94/0xb0 net/socket.c:968 sock_ioctl+0x2c2/0x440 net/socket.c:1058 vfs_ioctl fs/ioctl.c:45 [inline] do_vfs_ioctl+0x1b1/0x1520 fs/ioctl.c:685 SYSC_ioctl fs/ioctl.c:700 [inline] SyS_ioctl+0x8f/0xc0 fs/ioctl.c:691 Fixes: 7b9364050246 ("net, sched: convert Qdisc.refcnt from atomic_t to refcount_t") Signed-off-by: Eric Dumazet Reported-by: Dmitry Vyukov Cc: Reshetova, Elena Signed-off-by: David S. Miller --- include/net/sch_generic.h | 7 +++++++ net/sched/sch_api.c | 6 +++--- net/sched/sch_generic.c | 2 +- 3 files changed, 11 insertions(+), 4 deletions(-) diff --git a/include/net/sch_generic.h b/include/net/sch_generic.h index 67f815e5d525..c1109cdbbfa6 100644 --- a/include/net/sch_generic.h +++ b/include/net/sch_generic.h @@ -101,6 +101,13 @@ struct Qdisc { spinlock_t busylock ____cacheline_aligned_in_smp; }; +static inline void qdisc_refcount_inc(struct Qdisc *qdisc) +{ + if (qdisc->flags & TCQ_F_BUILTIN) + return; + refcount_inc(&qdisc->refcnt); +} + static inline bool qdisc_is_running(const struct Qdisc *qdisc) { return (raw_read_seqcount(&qdisc->running) & 1) ? true : false; diff --git a/net/sched/sch_api.c b/net/sched/sch_api.c index a3fa144b8648..4fb5a3222d0d 100644 --- a/net/sched/sch_api.c +++ b/net/sched/sch_api.c @@ -836,7 +836,7 @@ static int qdisc_graft(struct net_device *dev, struct Qdisc *parent, old = dev_graft_qdisc(dev_queue, new); if (new && i > 0) - refcount_inc(&new->refcnt); + qdisc_refcount_inc(new); if (!ingress) qdisc_destroy(old); @@ -847,7 +847,7 @@ skip: notify_and_destroy(net, skb, n, classid, dev->qdisc, new); if (new && !new->ops->attach) - refcount_inc(&new->refcnt); + qdisc_refcount_inc(new); dev->qdisc = new ? : &noop_qdisc; if (new && new->ops->attach) @@ -1256,7 +1256,7 @@ replay: if (q == p || (p && check_loop(q, p, 0))) return -ELOOP; - refcount_inc(&q->refcnt); + qdisc_refcount_inc(q); goto graft; } else { if (!q) diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c index 57ba406f1437..4ba6da5fb254 100644 --- a/net/sched/sch_generic.c +++ b/net/sched/sch_generic.c @@ -785,7 +785,7 @@ static void attach_default_qdiscs(struct net_device *dev) dev->priv_flags & IFF_NO_QUEUE) { netdev_for_each_tx_queue(dev, attach_one_default_qdisc, NULL); dev->qdisc = txq->qdisc_sleeping; - refcount_inc(&dev->qdisc->refcnt); + qdisc_refcount_inc(dev->qdisc); } else { qdisc = qdisc_create_dflt(txq, &mq_qdisc_ops, TC_H_ROOT); if (qdisc) {