Hello, I've observed that the `dd` command in Busybox uses `fprintf` directly 
within `dd_output_status`, which is bound to the USR1 signal handler.
Additionally, there exists a call chain: `make_human_readable` > `xasprintf` > 
`va_start/va_end` (or alternatively, `xasprintf` > `vasprintf` > `malloc`).  

To my knowledge, `fprintf`, `va_*` functions, and `malloc` are only MT-Safe but 
not AS-Safe. They should not be used in signal handlers.  
This might pose a potential security concern, but I'm not entirely sure.
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