[PATCH AUTOSEL 5.15 30/46] mrp: introduce active flags to prevent UAF when applicant uninit

Sasha Levin
2022-12-18T16:43:05Z

From: Schspa Shi <schspa@gmail.com>

[ Upstream commit ab0377803dafc58f1e22296708c1c28e309414d6 ]

The caller of del_timer_sync must prevent restarting of the timer, If
we have no this synchronization, there is a small probability that the
cancellation will not be successful.

And syzbot report the fellowing crash:
==================================================================
BUG: KASAN: use-after-free in hlist_add_head include/linux/list.h:929 [inline]
BUG: KASAN: use-after-free in enqueue_timer+0x18/0xa4 kernel/time/timer.c:605
Write at addr f9ff000024df6058 by task syz-fuzzer/2256
Pointer tag: [f9], memory tag: [fe]

CPU: 1 PID: 2256 Comm: syz-fuzzer Not tainted 6.1.0-rc5-syzkaller-00008-
ge01d50cbd6ee #0
Hardware name: linux,dummy-virt (DT)
Call trace:
dump_backtrace.part.0+0xe0/0xf0 arch/arm64/kernel/stacktrace.c:156
dump_backtrace arch/arm64/kernel/stacktrace.c:162 [inline]
show_stack+0x18/0x40 arch/arm64/kernel/stacktrace.c:163
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0x68/0x84 lib/dump_stack.c:106
print_address_description mm/kasan/report.c:284 [inline]
print_report+0x1a8/0x4a0 mm/kasan/report.c:395
kasan_report+0x94/0xb4 mm/kasan/report.c:495
__do_kernel_fault+0x164/0x1e0 arch/arm64/mm/fault.c:320
do_bad_area arch/arm64/mm/fault.c:473 [inline]
do_tag_check_fault+0x78/0x8c arch/arm64/mm/fault.c:749
do_mem_abort+0x44/0x94 arch/arm64/mm/fault.c:825
el1_abort+0x40/0x60 arch/arm64/kernel/entry-common.c:367
el1h_64_sync_handler+0xd8/0xe4 arch/arm64/kernel/entry-common.c:427
el1h_64_sync+0x64/0x68 arch/arm64/kernel/entry.S:576
hlist_add_head include/linux/list.h:929 [inline]
enqueue_timer+0x18/0xa4 kernel/time/timer.c:605
mod_timer+0x14/0x20 kernel/time/timer.c:1161
mrp_periodic_timer_arm net/802/mrp.c:614 [inline]
mrp_periodic_timer+0xa0/0xc0 net/802/mrp.c:627
call_timer_fn.constprop.0+0x24/0x80 kernel/time/timer.c:1474
expire_timers+0x98/0xc4 kernel/time/timer.c:1519

To fix it, we can introduce a new active flags to make sure the timer will
not restart.

Reported-by: syzbot+6fd64001c20aa99e34a4@syzkaller.appspotmail.com

Signed-off-by: Schspa Shi <schspa@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
include/net/mrp.h | 1 +
net/802/mrp.c | 18 +++++++++++++-----
2 files changed, 14 insertions(+), 5 deletions(-)

diff --git a/include/net/mrp.h b/include/net/mrp.h
index 1c308c034e1a..a8102661fd61 100644
--- a/include/net/mrp.h
+++ b/include/net/mrp.h
@@ -120,6 +120,7 @@ struct mrp_applicant {
struct sk_buff *pdu;
struct rb_root mad;
struct rcu_head rcu;
+ bool active;
};

struct mrp_port {
diff --git a/net/802/mrp.c b/net/802/mrp.c
index 35e04cc5390c..c10a432a5b43 100644
--- a/net/802/mrp.c
+++ b/net/802/mrp.c
@@ -606,7 +606,10 @@ static void mrp_join_timer(struct timer_list *t)
spin_unlock(&app->lock);

mrp_queue_xmit(app);
- mrp_join_timer_arm(app);
+ spin_lock(&app->lock);
+ if (likely(app->active))
+ mrp_join_timer_arm(app);
+ spin_unlock(&app->lock);
}

static void mrp_periodic_timer_arm(struct mrp_applicant *app)
@@ -620,11 +623,12 @@ static void mrp_periodic_timer(struct timer_list *t)
struct mrp_applicant *app = from_timer(app, t, periodic_timer);

spin_lock(&app->lock);
- mrp_mad_event(app, MRP_EVENT_PERIODIC);
- mrp_pdu_queue(app);
+ if (likely(app->active)) {
+ mrp_mad_event(app, MRP_EVENT_PERIODIC);
+ mrp_pdu_queue(app);
+ mrp_periodic_timer_arm(app);
+ }
spin_unlock(&app->lock);
-
- mrp_periodic_timer_arm(app);
}

static int mrp_pdu_parse_end_mark(struct sk_buff *skb, int *offset)
@@ -872,6 +876,7 @@ int mrp_init_applicant(struct net_device *dev, struct mrp_application *appl)
app->dev = dev;
app->app = appl;
app->mad = RB_ROOT;
+ app->active = true;
spin_lock_init(&app->lock);
skb_queue_head_init(&app->queue);
rcu_assign_pointer(dev->mrp_port->applicants[appl->type], app);
@@ -900,6 +905,9 @@ void mrp_uninit_applicant(struct net_device *dev, struct mrp_application *appl)

RCU_INIT_POINTER(port->applicants[appl->type], NULL);

+ spin_lock_bh(&app->lock);
+ app->active = false;
+ spin_unlock_bh(&app->lock);
/* Delete timer and generate a final TX event to flush out
* all pending messages before the applicant is gone.
*/
--
2.35.1