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    Subject[PATCH AUTOSEL 5.4 20/30] mrp: introduce active flags to prevent UAF when applicant uninit
    Date
    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 ef58b4a07190..c6c53370e390 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 5b804dbe2d08..486becf6c78d 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
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