ioctl SIOCGIFCONF causes qemu-aarch64-static to crash with "received signal outside vCPU context"

[Kan Li]

To reproduce it, compile the attached crash.c under aarch64 to a.out and execute on x86_64
qemu-aarch64-static ./a.out

It will print the following and crash:

socket=3
qemu:handle_cpu_signal received signal outside vCPU context @ pc=0x60038cd6
qemu:handle_cpu_signal received signal outside vCPU context @ pc=0x6000157a

The version of qemu-aarch64-static is

qemu-aarch64 version 3.0.0 (qemu-3.0.0-1.fc29)
Copyright (c) 2003-2017 Fabrice Bellard and the QEMU Project developers

But it did also happen in previous versions so it is not a regression but a bug existed ever since.

[Kan Li (likan)]

I was hit by this issue when I tried to run some Java program. And it turns out jdk sets the buf to NULL: http://hg.openjdk.java.net/jdk7/jdk7/jdk/file/887e525597f8/src/solaris/native/java/net/NetworkInterface.c#l1042

Setting to NULL is valid according to http://man7.org/linux/man-pages/man7/netdevice.7.html

But qemu doesn’t handle the case: https://github.com/qemu/qemu/blob/aa8e26de9617756febcbf794dda965df307fdaaa/linux-user/syscall.c#L4105

I guess qemu developers didn’t handle the case because the Linux kernel changed and they were based on behavior of old version: https://linux.die.net/man/7/netdevice

Please add the support for it otherwise a wide range of network related Java programs won’t run.

[Kan Li (likan)]

I sent out a patch: http://lists.nongnu.org/archive/html/qemu-devel/2018-10/msg01657.html
(Please ignore the other 2 identical patches. It was my first time sending out patches and I didn't know it was moderated so I sent it out multiple times).

[Kan Li (likan)]

I have patch at http://lists.nongnu.org/archive/html/qemu-devel/2018-10/msg05401.html, please let me know when it can be merged, thanks.

[Peter Maydell (pmaydell)]

Kan Li's patch was applied to master as commit 22e4a267a6627e5b5b, so this will be fixed in the upcoming QEMU 4.0 release.