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