git: 2af412767144 - stable/12 - netinet: allow UDP tunnels to be removed

The branch stable/12 has been updated by kp:

URL: https://cgit.FreeBSD.org/src/commit/?id=2af412767144ecaaef970c10a146209e521d3dca

commit 2af412767144ecaaef970c10a146209e521d3dca
Author:     Kristof Provost <kp@FreeBSD.org>
AuthorDate: 2022-02-15 10:49:39 +0000
Commit:     Kristof Provost <kp@FreeBSD.org>
CommitDate: 2022-02-26 08:26:15 +0000

    netinet: allow UDP tunnels to be removed
    
    udp_set_kernel_tunneling() rejects new callbacks if one is already set.
    Allow callbacks to be cleared. The use case for this is OpenVPN DCO,
    where the socket is opened by userspace and then adopted by the kernel
    to run the tunnel. If the DCO interface is removed but userspace does
    not close the socket (something the kernel cannot prevent) the installed
    callbacks could be called with an invalidated context.
    
    Allow new functions to be set, but only if they're NULL (i.e. allow the
    callback functions to be cleared).
    
    Reviewed by:    tuexen
    MFC after:      3 weeks
    Sponsored by:   Rubicon Communications, LLC ("Netgate")
    Differential Revision:  https://reviews.freebsd.org/D34288
    
    (cherry picked from commit 995cba5a0c9659e623b910429222ac2831a2ecca)
---
 sys/netinet/udp_usrreq.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/sys/netinet/udp_usrreq.c b/sys/netinet/udp_usrreq.c
index f57a9059a7db..3c98fa005520 100644
--- a/sys/netinet/udp_usrreq.c
+++ b/sys/netinet/udp_usrreq.c
@@ -1739,8 +1739,8 @@ udp_set_kernel_tunneling(struct socket *so, udp_tun_func_t f, udp_tun_icmp_t i,
 	KASSERT(inp != NULL, ("udp_set_kernel_tunneling: inp == NULL"));
 	INP_WLOCK(inp);
 	up = intoudpcb(inp);
-	if ((up->u_tun_func != NULL) ||
-	    (up->u_icmp_func != NULL)) {
+	if ((f != NULL || i != NULL) && ((up->u_tun_func != NULL) ||
+	    (up->u_icmp_func != NULL))) {
 		INP_WUNLOCK(inp);
 		return (EBUSY);
 	}