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Date:   Thu, 23 Jun 2022 20:20:25 +0800 (GMT+08:00)
From:   duoming@....edu.cn
To:     "Paolo Abeni" <pabeni@...hat.com>
Cc:     linux-hams@...r.kernel.org, ralf@...ux-mips.org,
        davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net 1/2] net: rose: fix UAF bugs caused by timer handler

Hello,

On Thu, 23 Jun 2022 11:13:41 +0200 Paolo Abeni wrote:

> > There are UAF bugs in rose_heartbeat_expiry(), rose_timer_expiry()
> > and rose_idletimer_expiry(). The root cause is that del_timer()
> > could not stop the timer handler that is running and the refcount
> > of sock is not managed properly.
> > 
> > One of the UAF bugs is shown below:
> > 
> >     (thread 1)          |        (thread 2)
> >                         |  rose_bind
> >                         |  rose_connect
> >                         |    rose_start_heartbeat
> > rose_release            |    (wait a time)
> >   case ROSE_STATE_0     |
> >   rose_destroy_socket   |  rose_heartbeat_expiry
> >     rose_stop_heartbeat |
> >     sock_put(sk)        |    ...
> >   sock_put(sk) // FREE  |
> >                         |    bh_lock_sock(sk) // USE
> > 
> > The sock is deallocated by sock_put() in rose_release() and
> > then used by bh_lock_sock() in rose_heartbeat_expiry().
> > 
> > Although rose_destroy_socket() calls rose_stop_heartbeat(),
> > it could not stop the timer that is running.
> > 
> > The KASAN report triggered by POC is shown below:
> > 
> > BUG: KASAN: use-after-free in _raw_spin_lock+0x5a/0x110
> > Write of size 4 at addr ffff88800ae59098 by task swapper/3/0
> > ...
> > Call Trace:
> >  <IRQ>
> >  dump_stack_lvl+0xbf/0xee
> >  print_address_description+0x7b/0x440
> >  print_report+0x101/0x230
> >  ? irq_work_single+0xbb/0x140
> >  ? _raw_spin_lock+0x5a/0x110
> >  kasan_report+0xed/0x120
> >  ? _raw_spin_lock+0x5a/0x110
> >  kasan_check_range+0x2bd/0x2e0
> >  _raw_spin_lock+0x5a/0x110
> >  rose_heartbeat_expiry+0x39/0x370
> >  ? rose_start_heartbeat+0xb0/0xb0
> >  call_timer_fn+0x2d/0x1c0
> >  ? rose_start_heartbeat+0xb0/0xb0
> >  expire_timers+0x1f3/0x320
> >  __run_timers+0x3ff/0x4d0
> >  run_timer_softirq+0x41/0x80
> >  __do_softirq+0x233/0x544
> >  irq_exit_rcu+0x41/0xa0
> >  sysvec_apic_timer_interrupt+0x8c/0xb0
> >  </IRQ>
> >  <TASK>
> >  asm_sysvec_apic_timer_interrupt+0x1b/0x20
> > RIP: 0010:default_idle+0xb/0x10
> > RSP: 0018:ffffc9000012fea0 EFLAGS: 00000202
> > RAX: 000000000000bcae RBX: ffff888006660f00 RCX: 000000000000bcae
> > RDX: 0000000000000001 RSI: ffffffff843a11c0 RDI: ffffffff843a1180
> > RBP: dffffc0000000000 R08: dffffc0000000000 R09: ffffed100da36d46
> > R10: dfffe9100da36d47 R11: ffffffff83cf0950 R12: 0000000000000000
> > R13: 1ffff11000ccc1e0 R14: ffffffff8542af28 R15: dffffc0000000000
> > ...
> > Allocated by task 146:
> >  __kasan_kmalloc+0xc4/0xf0
> >  sk_prot_alloc+0xdd/0x1a0
> >  sk_alloc+0x2d/0x4e0
> >  rose_create+0x7b/0x330
> >  __sock_create+0x2dd/0x640
> >  __sys_socket+0xc7/0x270
> >  __x64_sys_socket+0x71/0x80
> >  do_syscall_64+0x43/0x90
> >  entry_SYSCALL_64_after_hwframe+0x46/0xb0
> > 
> > Freed by task 152:
> >  kasan_set_track+0x4c/0x70
> >  kasan_set_free_info+0x1f/0x40
> >  ____kasan_slab_free+0x124/0x190
> >  kfree+0xd3/0x270
> >  __sk_destruct+0x314/0x460
> >  rose_release+0x2fa/0x3b0
> >  sock_close+0xcb/0x230
> >  __fput+0x2d9/0x650
> >  task_work_run+0xd6/0x160
> >  exit_to_user_mode_loop+0xc7/0xd0
> >  exit_to_user_mode_prepare+0x4e/0x80
> >  syscall_exit_to_user_mode+0x20/0x40
> >  do_syscall_64+0x4f/0x90
> >  entry_SYSCALL_64_after_hwframe+0x46/0xb0
> > 
> > This patch adds refcount of sock when we use functions
> > such as rose_start_heartbeat() and so on to start timer,
> > and decreases the refcount of sock when timer is finished
> > or deleted by functions such as rose_stop_heartbeat()
> > and so on. As a result, the UAF bugs could be mitigated.
> > 
> > Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> > Signed-off-by: Duoming Zhou <duoming@....edu.cn>
> > Tested-by: Duoming Zhou <duoming@....edu.cn>
> > ---
> >  net/rose/rose_timer.c | 22 +++++++++++++---------
> >  1 file changed, 13 insertions(+), 9 deletions(-)
> > 
> > diff --git a/net/rose/rose_timer.c b/net/rose/rose_timer.c
> > index b3138fc2e55..18d1912520b 100644
> > --- a/net/rose/rose_timer.c
> > +++ b/net/rose/rose_timer.c
> > @@ -36,7 +36,7 @@ void rose_start_heartbeat(struct sock *sk)
> >  	sk->sk_timer.function = rose_heartbeat_expiry;
> >  	sk->sk_timer.expires  = jiffies + 5 * HZ;
> >  
> > -	add_timer(&sk->sk_timer);
> > +	sk_reset_timer(sk, &sk->sk_timer, sk->sk_timer.expires);
> >  }
> >  
> >  void rose_start_t1timer(struct sock *sk)
> > @@ -48,7 +48,7 @@ void rose_start_t1timer(struct sock *sk)
> >  	rose->timer.function = rose_timer_expiry;
> >  	rose->timer.expires  = jiffies + rose->t1;
> >  
> > -	add_timer(&rose->timer);
> > +	sk_reset_timer(sk, &rose->timer, rose->timer.expires);
> >  }
> >  
> >  void rose_start_t2timer(struct sock *sk)
> > @@ -60,7 +60,7 @@ void rose_start_t2timer(struct sock *sk)
> >  	rose->timer.function = rose_timer_expiry;
> >  	rose->timer.expires  = jiffies + rose->t2;
> >  
> > -	add_timer(&rose->timer);
> > +	sk_reset_timer(sk, &rose->timer, rose->timer.expires);
> >  }
> >  
> >  void rose_start_t3timer(struct sock *sk)
> > @@ -72,7 +72,7 @@ void rose_start_t3timer(struct sock *sk)
> >  	rose->timer.function = rose_timer_expiry;
> >  	rose->timer.expires  = jiffies + rose->t3;
> >  
> > -	add_timer(&rose->timer);
> > +	sk_reset_timer(sk, &rose->timer, rose->timer.expires);
> >  }
> >  
> >  void rose_start_hbtimer(struct sock *sk)
> > @@ -84,7 +84,7 @@ void rose_start_hbtimer(struct sock *sk)
> >  	rose->timer.function = rose_timer_expiry;
> >  	rose->timer.expires  = jiffies + rose->hb;
> >  
> > -	add_timer(&rose->timer);
> > +	sk_reset_timer(sk, &rose->timer, rose->timer.expires);
> >  }
> >  
> >  void rose_start_idletimer(struct sock *sk)
> > @@ -97,23 +97,23 @@ void rose_start_idletimer(struct sock *sk)
> >  		rose->idletimer.function = rose_idletimer_expiry;
> >  		rose->idletimer.expires  = jiffies + rose->idle;
> >  
> > -		add_timer(&rose->idletimer);
> > +		sk_reset_timer(sk, &rose->idletimer, rose->idletimer.expires);
> 
> A few lines above there is still a 'del_timer(&rose->idletimer);' call
> which must be converted to sk_stop_timer(), otherwise there will be a
> possible sk reference leak.
> 
> There are other del_timer(&rose->timer) that need conversion.

Thank you for your time and suggestions! I will convert 'del_timer(&rose->idletimer);'
and so on to sk_stop_timer().

Best regards,
Duoming Zhou

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