Re: [PATCH] util/error, hw/net/virtio-net: fix NULL pointer dereference in error_vprepend

[Markus Armbruster <armbru@redhat.com>]

First, please read docs/devel/code-provenance.rst section "Use of
AI-generated content".

I'm not looking at the patches, only the commit message.

Николай Зорин <zorin@swemel.ru> writes:

> SWSA#b0709cee-9722-4603-a30c-dc857dc87961
>
> The `error_vprepend()` function modifies the error message inside an
> existing Error object. However, it only validated if the `errp` pointer
> itself was non-NULL, missing a check for whether the underlying Error
> object `*errp` is `NULL`.

This is nonsense.  error_vprepend() and error_prepend() modify an error.
They must not be called when there is none.  The check isn't missing.
Adding it makes the functions "work" papers over bugs.

> Calling `error_reportf_err(local_error, ...)` when `local_error` is `NULL`
> invokes `error_vprepend(&local_error, ...)`, which subsequently crashes
> via a `NULL` pointer dereference during `(*errp)->msg` access.
>
> Fix `util/error.c` by adding a defensive `!*errp` check inside 
> `error_vprepend()`.
>
> Additionally, fix the invalid error reporting patterns in 
> `hw/net/virtio-net.c`:
> - In `vhost_user_net_save_state()` and `vhost_user_net_load_state()`, when
>    `vhdev == NULL`, calling `error_reportf_err()` with an unallocated/NULL
>    `local_error` is incorrect and unsafe. Replace it with a straightforward
>    `error_report()` call.

Both uses of error_reportf_err() are indeed wrong.

> - Fix a cosmetic double-space typo in "Error loading  back-end state".

Worth cleaning up.

> Signed-off-by: Nikolay N Zorin <zorin@swemel.ru>