[PATCH net-net] tun: Assign missing bpf_net_context.

[Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>]

During the introduction of struct bpf_net_context handling for
XDP-redirect, the tun driver has been missed.

Set the bpf_net_context before invoking BPF XDP program within the TUN
driver.

Reported-by: syzbot+0b5c75599f1d872bea6f@xxxxxxxxxxxxxxxxxxxxxxxxx
Reported-by: syzbot+5ae46b237278e2369cac@xxxxxxxxxxxxxxxxxxxxxxxxx
Reported-by: syzbot+c1e04a422bbc0f0f2921@xxxxxxxxxxxxxxxxxxxxxxxxx
Fixes: 401cb7dae8130 ("net: Reference bpf_redirect_info via task_struct on PREEMPT_RT.")
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
---
 drivers/net/tun.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 9254bca2813dc..df4dd6b7479e1 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -1661,6 +1661,7 @@ static struct sk_buff *tun_build_skb(struct tun_struct *tun,
 				     int len, int *skb_xdp)
 {
 	struct page_frag *alloc_frag = &current->task_frag;
+	struct bpf_net_context __bpf_net_ctx, *bpf_net_ctx;
 	struct bpf_prog *xdp_prog;
 	int buflen = SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
 	char *buf;
@@ -1700,6 +1701,7 @@ static struct sk_buff *tun_build_skb(struct tun_struct *tun,
 
 	local_bh_disable();
 	rcu_read_lock();
+	bpf_net_ctx = bpf_net_ctx_set(&__bpf_net_ctx);
 	xdp_prog = rcu_dereference(tun->xdp_prog);
 	if (xdp_prog) {
 		struct xdp_buff xdp;
@@ -1728,12 +1730,14 @@ static struct sk_buff *tun_build_skb(struct tun_struct *tun,
 		pad = xdp.data - xdp.data_hard_start;
 		len = xdp.data_end - xdp.data;
 	}
+	bpf_net_ctx_clear(bpf_net_ctx);
 	rcu_read_unlock();
 	local_bh_enable();
 
 	return __tun_build_skb(tfile, alloc_frag, buf, buflen, len, pad);
 
 out:
+	bpf_net_ctx_clear(bpf_net_ctx);
 	rcu_read_unlock();
 	local_bh_enable();
 	return NULL;
@@ -1914,20 +1918,24 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile,
 	skb_record_rx_queue(skb, tfile->queue_index);
 
 	if (skb_xdp) {
+		struct bpf_net_context __bpf_net_ctx, *bpf_net_ctx;
 		struct bpf_prog *xdp_prog;
 		int ret;
 
 		local_bh_disable();
 		rcu_read_lock();
+		bpf_net_ctx = bpf_net_ctx_set(&__bpf_net_ctx);
 		xdp_prog = rcu_dereference(tun->xdp_prog);
 		if (xdp_prog) {
 			ret = do_xdp_generic(xdp_prog, &skb);
 			if (ret != XDP_PASS) {
+				bpf_net_ctx_clear(bpf_net_ctx);
 				rcu_read_unlock();
 				local_bh_enable();
 				goto unlock_frags;
 			}
 		}
+		bpf_net_ctx_clear(bpf_net_ctx);
 		rcu_read_unlock();
 		local_bh_enable();
 	}
@@ -2566,6 +2574,7 @@ static int tun_sendmsg(struct socket *sock, struct msghdr *m, size_t total_len)
 
 	if (m->msg_controllen == sizeof(struct tun_msg_ctl) &&
 	    ctl && ctl->type == TUN_MSG_PTR) {
+		struct bpf_net_context __bpf_net_ctx, *bpf_net_ctx;
 		struct tun_page tpage;
 		int n = ctl->num;
 		int flush = 0, queued = 0;
@@ -2574,6 +2583,7 @@ static int tun_sendmsg(struct socket *sock, struct msghdr *m, size_t total_len)
 
 		local_bh_disable();
 		rcu_read_lock();
+		bpf_net_ctx = bpf_net_ctx_set(&__bpf_net_ctx);
 
 		for (i = 0; i < n; i++) {
 			xdp = &((struct xdp_buff *)ctl->ptr)[i];
@@ -2588,6 +2598,7 @@ static int tun_sendmsg(struct socket *sock, struct msghdr *m, size_t total_len)
 		if (tfile->napi_enabled && queued > 0)
 			napi_schedule(&tfile->napi);
 
+		bpf_net_ctx_clear(bpf_net_ctx);
 		rcu_read_unlock();
 		local_bh_enable();
 
-- 
2.45.2