From 5a5abb1fa3b05dd6aa821525832644c1e7d2905f Mon Sep 17 00:00:00 2001 From: Daniel Borkmann Date: Thu, 31 Mar 2016 02:13:18 +0200 Subject: tun, bpf: fix suspicious RCU usage in tun_{attach, detach}_filter 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: [] 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] [] dump_stack+0x85/0xc8 [ 52.765784] [] lockdep_rcu_suspicious+0xd5/0x110 [ 52.765792] [] sk_detach_filter+0x82/0x90 [ 52.765801] [] tun_detach_filter+0x35/0x90 [tun] [ 52.765810] [] __tun_chr_ioctl+0x354/0x1130 [tun] [ 52.765818] [] ? selinux_file_ioctl+0x130/0x210 [ 52.765827] [] tun_chr_ioctl+0x13/0x20 [tun] [ 52.765834] [] do_vfs_ioctl+0x96/0x690 [ 52.765843] [] ? security_file_ioctl+0x43/0x60 [ 52.765850] [] SyS_ioctl+0x79/0x90 [ 52.765858] [] do_syscall_64+0x62/0x140 [ 52.765866] [] 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. Reported-by: Sasha Levin Signed-off-by: Daniel Borkmann Signed-off-by: David S. Miller --- drivers/net/tun.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) (limited to 'drivers') diff --git a/drivers/net/tun.c b/drivers/net/tun.c index afdf950617c3..510e90a6bb26 100644 --- a/drivers/net/tun.c +++ b/drivers/net/tun.c @@ -622,7 +622,8 @@ static int tun_attach(struct tun_struct *tun, struct file *file, bool skip_filte /* Re-attach the filter to persist device */ if (!skip_filter && (tun->filter_attached == true)) { - err = sk_attach_filter(&tun->fprog, tfile->socket.sk); + err = __sk_attach_filter(&tun->fprog, tfile->socket.sk, + lockdep_rtnl_is_held()); if (!err) goto out; } @@ -1822,7 +1823,7 @@ static void tun_detach_filter(struct tun_struct *tun, int n) for (i = 0; i < n; i++) { tfile = rtnl_dereference(tun->tfiles[i]); - sk_detach_filter(tfile->socket.sk); + __sk_detach_filter(tfile->socket.sk, lockdep_rtnl_is_held()); } tun->filter_attached = false; @@ -1835,7 +1836,8 @@ static int tun_attach_filter(struct tun_struct *tun) for (i = 0; i < tun->numqueues; i++) { tfile = rtnl_dereference(tun->tfiles[i]); - ret = sk_attach_filter(&tun->fprog, tfile->socket.sk); + ret = __sk_attach_filter(&tun->fprog, tfile->socket.sk, + lockdep_rtnl_is_held()); if (ret) { tun_detach_filter(tun, i); return ret; -- cgit v1.2.3-59-g8ed1b