From 3f6be9c84782a0943ea21a8a6f8a5d055b65f2d5 Mon Sep 17 00:00:00 2001 Message-Id: <3f6be9c84782a0943ea21a8a6f8a5d055b65f2d5.1619018363.git.crobinso@redhat.com> From: Cole Robinson Date: Wed, 21 Apr 2021 11:12:07 -0400 Subject: [PATCH-for-6.0] net: tap: fix crash on hotplug Attempting to hotplug a tap nic with libvirt will crash qemu: $ sudo virsh attach-interface f32 network default error: Failed to attach interface error: Unable to read from monitor: Connection reset by peer 0x000055875b7f3a99 in tap_send (opaque=0x55875e39eae0) at ../net/tap.c:206 206 if (!s->nc.peer->do_not_pad) { gdb$ bt s->nc.peer may not be set at this point. This seems to be an expected case, as qemu_send_packet_* explicitly checks for NULL s->nc.peer later. Fix it by checking for s->nc.peer here too. Padding is applied if s->nc.peer is not set. https://bugzilla.redhat.com/show_bug.cgi?id=1949786 Fixes: 969e50b61a2 Signed-off-by: Cole Robinson --- * Or should we skip padding if nc.peer is unset? I didn't dig into it * tap-win3.c and slirp.c may need a similar fix, but the slirp case didn't crash in a simple test. net/tap.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/net/tap.c b/net/tap.c index dd42ac6134..937559dbb8 100644 --- a/net/tap.c +++ b/net/tap.c @@ -203,7 +203,7 @@ static void tap_send(void *opaque) size -= s->host_vnet_hdr_len; } - if (!s->nc.peer->do_not_pad) { + if (!s->nc.peer || !s->nc.peer->do_not_pad) { if (eth_pad_short_frame(min_pkt, &min_pktsz, buf, size)) { buf = min_pkt; size = min_pktsz; -- 2.31.1