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Registered Address: Red Hat UK Ltd, Amberley Place, 107-111 Peascod Street, Windsor, Berkshire, SI4 1TE, United Kingdom. Registered in England and Wales under Company Registration No. 3798903 From: David Howells To: Marc Dionne cc: dhowells@redhat.com, "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , linux-afs@lists.infradead.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH net v3] rxrpc: Fix use of Don't Fragment flag Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-ID: <1581851.1704813048.1@warthog.procyon.org.uk> Content-Transfer-Encoding: quoted-printable Date: Tue, 09 Jan 2024 15:10:48 +0000 Message-ID: <1581852.1704813048@warthog.procyon.org.uk> X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.3 = rxrpc normally has the Don't Fragment flag set on the UDP packets it transmits, except when it has decided that DATA packets aren't getting through - in which case it turns it off just for the DATA transmissions. This can be a problem, however, for RESPONSE packets that convey authentication and crypto data from the client to the server as ticket may be larger than can fit in the MTU. In such a case, rxrpc gets itself into an infinite loop as the sendmsg returns an error (EMSGSIZE), which causes rxkad_send_response() to return -EAGAIN - and the CHALLENGE packet is put back on the Rx queue to retry, leading to the I/O thread endlessly attempting to perform the transmission= . Fix this by disabling DF on RESPONSE packets for now. The use of DF and best data MTU determination needs reconsidering at some point in the future. Fixes: 17926a79320a ("[AF_RXRPC]: Provide secure RxRPC sockets for use by = userspace and kernel both") Reported-by: Marc Dionne Signed-off-by: David Howells cc: "David S. Miller" cc: Eric Dumazet cc: Jakub Kicinski cc: Paolo Abeni cc: linux-afs@lists.infradead.org cc: netdev@vger.kernel.org --- net/rxrpc/ar-internal.h | 1 + net/rxrpc/local_object.c | 13 ++++++++++++- net/rxrpc/output.c | 6 ++---- net/rxrpc/rxkad.c | 2 ++ 4 files changed, 17 insertions(+), 5 deletions(-) diff --git a/net/rxrpc/ar-internal.h b/net/rxrpc/ar-internal.h index e8e14c6f904d..e8b43408136a 100644 --- a/net/rxrpc/ar-internal.h +++ b/net/rxrpc/ar-internal.h @@ -1076,6 +1076,7 @@ void rxrpc_send_version_request(struct rxrpc_local *= local, /* * local_object.c */ +void rxrpc_local_dont_fragment(const struct rxrpc_local *local, bool set)= ; struct rxrpc_local *rxrpc_lookup_local(struct net *, const struct sockadd= r_rxrpc *); struct rxrpc_local *rxrpc_get_local(struct rxrpc_local *, enum rxrpc_loca= l_trace); struct rxrpc_local *rxrpc_get_local_maybe(struct rxrpc_local *, enum rxrp= c_local_trace); diff --git a/net/rxrpc/local_object.c b/net/rxrpc/local_object.c index c553a30e9c83..34d307368135 100644 --- a/net/rxrpc/local_object.c +++ b/net/rxrpc/local_object.c @@ -36,6 +36,17 @@ static void rxrpc_encap_err_rcv(struct sock *sk, struct= sk_buff *skb, int err, return ipv6_icmp_error(sk, skb, err, port, info, payload); } = +/* + * Set or clear the Don't Fragment flag on a socket. + */ +void rxrpc_local_dont_fragment(const struct rxrpc_local *local, bool set) +{ + if (set) + ip_sock_set_mtu_discover(local->socket->sk, IP_PMTUDISC_DO); + else + ip_sock_set_mtu_discover(local->socket->sk, IP_PMTUDISC_DONT); +} + /* * Compare a local to an address. Return -ve, 0 or +ve to indicate less = than, * same or greater than. @@ -203,7 +214,7 @@ static int rxrpc_open_socket(struct rxrpc_local *local= , struct net *net) ip_sock_set_recverr(usk); = /* we want to set the don't fragment bit */ - ip_sock_set_mtu_discover(usk, IP_PMTUDISC_DO); + rxrpc_local_dont_fragment(local, true); = /* We want receive timestamps. */ sock_enable_timestamps(usk); diff --git a/net/rxrpc/output.c b/net/rxrpc/output.c index 5e53429c6922..a0906145e829 100644 --- a/net/rxrpc/output.c +++ b/net/rxrpc/output.c @@ -494,14 +494,12 @@ int rxrpc_send_data_packet(struct rxrpc_call *call, = struct rxrpc_txbuf *txb) switch (conn->local->srx.transport.family) { case AF_INET6: case AF_INET: - ip_sock_set_mtu_discover(conn->local->socket->sk, - IP_PMTUDISC_DONT); + rxrpc_local_dont_fragment(conn->local, false); rxrpc_inc_stat(call->rxnet, stat_tx_data_send_frag); ret =3D do_udp_sendmsg(conn->local->socket, &msg, len); conn->peer->last_tx_at =3D ktime_get_seconds(); = - ip_sock_set_mtu_discover(conn->local->socket->sk, - IP_PMTUDISC_DO); + rxrpc_local_dont_fragment(conn->local, true); break; = default: diff --git a/net/rxrpc/rxkad.c b/net/rxrpc/rxkad.c index 1bf571a66e02..b52dedcebce0 100644 --- a/net/rxrpc/rxkad.c +++ b/net/rxrpc/rxkad.c @@ -724,7 +724,9 @@ static int rxkad_send_response(struct rxrpc_connection= *conn, serial =3D atomic_inc_return(&conn->serial); whdr.serial =3D htonl(serial); = + rxrpc_local_dont_fragment(conn->local, false); ret =3D kernel_sendmsg(conn->local->socket, &msg, iov, 3, len); + rxrpc_local_dont_fragment(conn->local, true); if (ret < 0) { trace_rxrpc_tx_fail(conn->debug_id, serial, ret, rxrpc_tx_point_rxkad_response);