What can we learn from the recently disclosed vulnerabilites in systemd?

<https://www.openwall.com/lists/oss-security/2019/01/09/3>

I'm not a security expert, nor have I understood all the details.

But there's one thing that really stands out:

> ... Surprised by the heavy usage of alloca() in journald, ...

Heavy usage of `alloca()`? Let's have a look at the manpage:

> DESCRIPTION
>        The  alloca()  function  allocates  size  bytes of space in the
>        stack frame of the caller.  This temporary space  is  automati‐
>        cally  freed  when the function that called alloca() returns to
>        its caller.
> 
> RETURN VALUE
>        The alloca() function returns a pointer to the beginning of the
>        allocated space.  If the allocation causes stack overflow, pro‐
>        gram behavior is undefined.
> ...
>
> NOTES
>        The  alloca() function is machine- and compiler-dependent.  For
>        certain applications, its use can improve  efficiency  compared
>        to the use of malloc(3) plus free(3).  In certain cases, it can
>        also simplify memory  deallocation  in  applications  that  use
>        longjmp(3)  or  siglongjmp(3).   Otherwise, its use is discour‐
>        aged.


`alloca()` never returns an error. If it fails, then it fails, and
you're screwed. The manpage explicitly discourages using it.

Okay then. Never use `alloca()`, if you ask me.