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Date: Thu, 24 Aug 2017 21:12:28 -0700
From: Eric Dumazet <eric.dumazet@...il.com>
To: David Miller <davem@...emloft.net>
Cc: netdev <netdev@...r.kernel.org>,
Cong Wang <xiyou.wangcong@...il.com>,
Jiri Pirko <jiri@...nulli.us>,
Reshetova Elena <elena.reshetova@...el.com>,
Jamal Hadi Salim <jhs@...atatu.com>
Subject: [PATCH net] net_sched: fix a refcount_t issue with noop_qdisc
From: Eric Dumazet <edumazet@...gle.com>
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 <edumazet@...gle.com>
Reported-by: Dmitry Vyukov <dvyukov@...gle.com>
Cc: Reshetova, Elena <elena.reshetova@...el.com>
---
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 67f815e5d52517390226bc3531b1ea7b5f1020bc..c1109cdbbfa6afb9aff0d6033aef7b615630ffc1 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 a3fa144b864871088209386fd573bded1886432f..4fb5a3222d0d324167f079f755be14eb028b4a50 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 @@ static int qdisc_graft(struct net_device *dev, struct Qdisc *parent,
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 @@ static int tc_modify_qdisc(struct sk_buff *skb, struct nlmsghdr *n,
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 57ba406f1437323a4ba172d52f14a8b687b86708..4ba6da5fb2546c35ad48fe1f3632df8ca9957b34 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) {
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