[OSS-Fuzz] Assertion Failure: !in6_zero(&ip_addr) (#111)

[Alexander Bulekov <alxndr@bu.edu>]

Hi,
Forwarding this along to the list, so it doesn't get burried during the
gitlab issue migration.

----- Forwarded message from "Alexander Bulekov (@a1xndr)" <gitlab@mg.gitlab.com> -----

Alexander Bulekov created an issue: https://gitlab.com/qemu-project/qemu/-/issues/111

Hello,
Reproducer
```
cat << EOF | ./qemu-system-i386 -display none -machine accel=qtest, -m \
512M -M q35 -nodefaults -device e1000e,netdev=net0 -netdev user,id=net0 \
-qtest stdio
outl 0xcf8 0x80000813
outl 0xcfc 0x56
outl 0xcf8 0x80000801
outl 0xcfc 0x06000000
write 0x56000403 0x1 0x02
write 0x5600042b 0x1 0x80
write 0x20a 0x1 0x86
write 0x20b 0x1 0xdd
write 0x20c 0x1 0x60
write 0x212 0x1 0x11
write 0x213 0x1 0x01
write 0x224 0x1 0xfe
write 0x225 0x1 0xc0
write 0x233 0x1 0x02
write 0x237 0x1 0x45
write 0x23d 0x1 0x01
write 0xb 0x1 0x24
write 0x10 0x1 0xfe
write 0x11 0x1 0x01
write 0x19 0x1 0x01
write 0x1a 0x1 0x10
write 0x1b 0x1 0x25
write 0x5600043a 0x1 0x04
EOF
```

Stack-trace:
```
SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior ../net/eth.c:374:27 in
../net/eth.c:375:27: runtime error: member access within misaligned address 0x631000014846 for type 'struct ip6_header', which requires 4 byte alignment
0x631000014846: note: pointer points here
 00 00 11 11 60 00  00 00 00 00 11 11 00 00  00 00 00 00 00 00 00 00  00 00 00 00 00 00 fe c0  00 00
             ^
SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior ../net/eth.c:375:27 in
qemu-fuzz-i386: ../slirp/src/ndp_table.c:59: _Bool ndp_table_search(Slirp *, struct in6_addr, uint8_t *): Assertion `!in6_zero(&ip_addr)' failed.

#8 in __assert_fail assert/assert.c:101:3
#9 in ndp_table_search /slirp/src/ndp_table.c:59:5
#10 in if_encap6 /slirp/src/slirp.c:926:10
#11 in if_encap /slirp/src/slirp.c:967:15
#12 in if_start /slirp/src/if.c:183:45
#13 in ip6_output /slirp/src/ip6_output.c:35:9
#14 in tftp_udp_output /slirp/src/tftp.c:161:9
#15 in tftp_send_error /slirp/src/tftp.c:223:5
#16 in tftp_handle_rrq /slirp/src/tftp.c
#17 in tftp_input /slirp/src/tftp.c:453:9
#18 in udp6_input /slirp/src/udp6.c:81:9
#19 in slirp_input /slirp/src/slirp.c:847:13
#20 in net_slirp_receive /net/slirp.c:136:5
#21 in nc_sendv_compat /net/net.c
#22 in qemu_deliver_packet_iov /net/net.c:765:15
#23 in qemu_net_queue_deliver_iov /net/queue.c:179:11
#24 in qemu_net_queue_send_iov /net/queue.c:246:11
#25 in net_tx_pkt_sendv /hw/net/net_tx_pkt.c:558:9
#26 in net_tx_pkt_send /hw/net/net_tx_pkt.c:633:9
#27 in e1000e_tx_pkt_send /hw/net/e1000e_core.c:659:16
#28 in e1000e_process_tx_desc /hw/net/e1000e_core.c:736:17
#29 in e1000e_start_xmit /hw/net/e1000e_core.c:927:9
#30 in e1000e_set_tdt /hw/net/e1000e_core.c:2444:9
#31 in e1000e_core_write /hw/net/e1000e_core.c:3256:9
#32 in memory_region_write_accessor /softmmu/memory.c:491:5
#33 in access_with_adjusted_size /softmmu/memory.c:552:18
#34 in memory_region_dispatch_write /softmmu/memory.c
#35 in flatview_write_continue /softmmu/physmem.c:2746:23
#36 in flatview_write /softmmu/physmem.c:2786:14
#37 in address_space_write /softmmu/physmem.c:2878:18
```

Test-case:
```
/*
 * Autogenerated Fuzzer Test Case
 *
 * Copyright (c) 2021 <name of author>
 *
 * This work is licensed under the terms of the GNU GPL, version 2 or later.
 * See the COPYING file in the top-level directory.
 */

#include "qemu/osdep.h"

#include "libqos/libqtest.h"

static void test_fuzz(void)
{
    QTestState *s = qtest_init("-display none , -m 512M -M q35 -nodefaults -device "
                               "e1000e,netdev=net0 -netdev user,id=net0");
    qtest_outl(s, 0xcf8, 0x80000813);
    qtest_outl(s, 0xcfc, 0x56);
    qtest_outl(s, 0xcf8, 0x80000801);
    qtest_outl(s, 0xcfc, 0x06000000);
    qtest_bufwrite(s, 0x56000403, "\x02", 0x1);
    qtest_bufwrite(s, 0x5600042b, "\x80", 0x1);
    qtest_bufwrite(s, 0x20a, "\x86", 0x1);
    qtest_bufwrite(s, 0x20b, "\xdd", 0x1);
    qtest_bufwrite(s, 0x20c, "\x60", 0x1);
    qtest_bufwrite(s, 0x212, "\x11", 0x1);
    qtest_bufwrite(s, 0x213, "\x01", 0x1);
    qtest_bufwrite(s, 0x224, "\xfe", 0x1);
    qtest_bufwrite(s, 0x225, "\xc0", 0x1);
    qtest_bufwrite(s, 0x233, "\x02", 0x1);
    qtest_bufwrite(s, 0x237, "\x45", 0x1);
    qtest_bufwrite(s, 0x23d, "\x01", 0x1);
    qtest_bufwrite(s, 0xb, "\x24", 0x1);
    qtest_bufwrite(s, 0x10, "\xfe", 0x1);
    qtest_bufwrite(s, 0x11, "\x01", 0x1);
    qtest_bufwrite(s, 0x19, "\x01", 0x1);
    qtest_bufwrite(s, 0x1a, "\x10", 0x1);
    qtest_bufwrite(s, 0x1b, "\x25", 0x1);
    qtest_bufwrite(s, 0x5600043a, "\x04", 0x1);
    qtest_quit(s);
}
int main(int argc, char **argv)
{
    const char *arch = qtest_get_arch();

    g_test_init(&argc, &argv, NULL);

    if (strcmp(arch, "i386") == 0) {
        qtest_add_func("fuzz/test_fuzz", test_fuzz);
    }

    return g_test_run();
}
```

OSS-Fuzz Report: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=33873