Re: [PATCH net 1/2] net: rose: fix UAF bugs caused by timer handler

From: duoming
Date: Thu Jun 23 2022 - 08:20:40 EST

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@xxxxxxxxxx>
> > Tested-by: Duoming Zhou <duoming@xxxxxxxxxx>
> > ---
> > 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