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This bug was initially created as a copy of Bug #1867739

I am copying this bug because: 

The crash is hit with RHEL-8.3.0 (QEMU 4.2 upstream). It's worth fixing in it in RHEL-8.3.1.

Description of problem:

`-prom-env` takes raw strings from the command-line and passes them through unvalidated into the NVRAM. It's possible to cause QEMU to abort by passing it malformed input.

```
ppc64-softmmu/qemu-system-ppc64 $(for ((x=0;x<128;x++)); do \
 echo -n " -prom-env "$(for ((y=0;y<1024;y++)); do echo -n x ; done) ; \
done)
free(): invalid next size (normal)
Aborted (core dumped)
```

Version-Release number of selected component (if applicable):

Observed upstream as of 5.1-rc4.

Expected results: QEMU performs some light validation of either the user's input such that QEMU does not crash. (What the guest does is another story.)

Reproduced the issue with old builds
qemu-kvm-4.2.0-34.module+el8.3.0+7976+077be4ec.ppc64le
verified the bug with the following build
qemu-kvm-4.2.0-35.module+el8.4.0+8453+f5da6c50.ppc64le

[root@ibm-p9wr-02 qemu-kvm]# /usr/libexec/qemu-kvm $(for ((x=0;x<128;x++)); do \
>  echo -n " -prom-env "$(for ((y=0;y<1024;y++)); do echo -n x ; done) ; \
> done)
qemu-kvm: NVRAM is too small. Try to pass less data to -prom-env

The original issue has been fixed, there's no coredump anymore, thanks.

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory (Moderate: virt:rhel and virt-devel:rhel security, bug fix, and enhancement update), and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://access.redhat.com/errata/RHSA-2021:1762