On 03/31/2016, 02:13 AM, Daniel Borkmann wrote:
> Sasha Levin reported a suspicious rcu_dereference_protected() warning
> found while fuzzing with trinity that is similar to this one:
>
> [ 52.765684] net/core/filter.c:2262 suspicious
> rcu_dereference_protected() usage!
> [ 52.765688] other info that might help us debug this:
> [ 52.765695] rcu_scheduler_active = 1, debug_locks = 1
> [ 52.765701] 1 lock held by a.out/1525:
> [ 52.765704] #0: (rtnl_mutex){+.+.+.}, at: [<ffffffff816a64b7>]
> rtnl_lock+0x17/0x20
> [ 52.765721] stack backtrace:
> [ 52.765728] CPU: 1 PID: 1525 Comm: a.out Not tainted 4.5.0+ #264
> [...]
> [ 52.765768] Call Trace:
> [ 52.765775] [<ffffffff813e488d>] dump_stack+0x85/0xc8
> [ 52.765784] [<ffffffff810f2fa5>] lockdep_rcu_suspicious+0xd5/0x110
> [ 52.765792] [<ffffffff816afdc2>] sk_detach_filter+0x82/0x90
> [ 52.765801] [<ffffffffa0883425>] tun_detach_filter+0x35/0x90 [tun]
> [ 52.765810] [<ffffffffa0884ed4>] __tun_chr_ioctl+0x354/0x1130 [tun]
> [ 52.765818] [<ffffffff8136fed0>] ? selinux_file_ioctl+0x130/0x210
> [ 52.765827] [<ffffffffa0885ce3>] tun_chr_ioctl+0x13/0x20 [tun]
> [ 52.765834] [<ffffffff81260ea6>] do_vfs_ioctl+0x96/0x690
> [ 52.765843] [<ffffffff81364af3>] ? security_file_ioctl+0x43/0x60
> [ 52.765850] [<ffffffff81261519>] SyS_ioctl+0x79/0x90
> [ 52.765858] [<ffffffff81003ba2>] do_syscall_64+0x62/0x140
> [ 52.765866] [<ffffffff817d563f>] entry_SYSCALL64_slow_path+0x25/0x25
>
> Same can be triggered with PROVE_RCU (+ PROVE_RCU_REPEATEDLY) enabled
> from tun_attach_filter() when user space calls ioctl(tun_fd, TUN{ATTACH,
> DETACH}FILTER, ...) for adding/removing a BPF filter on tap devices.
>
> Since the fix in f91ff5b9ff52 ("net: sk_{detach|attach}_filter() rcu
> fixes") sk_attach_filter()/sk_detach_filter() now dereferences the
> filter with rcu_dereference_protected(), checking whether socket lock
> is held in control path.
>
> Since its introduction in 994051625981 ("tun: socket filter support"),
> tap filters are managed under RTNL lock from __tun_chr_ioctl(). Thus the
> sock_owned_by_user(sk) doesn't apply in this specific case and therefore
> triggers the false positive.
>
> Extend the BPF API with __sk_attach_filter()/__sk_detach_filter() pair
> that is used by tap filters and pass in lockdep_rtnl_is_held() for the
> rcu_dereference_protected() checks instead.
It seems to be gone with this patch here.
thanks,
--
js
suse labs
