[libvirt] [PATCH 1/3] vircommand: Ensure buffers are NULL-terminated

[Daniel P. Berrangé]

On Tue, Feb 05, 2019 at 04:16:21PM +0100, Andrea Bolognani wrote:
> The memory allocated by VIR_REALLOC_N() is uninitialized,
> which means it's not possible to figure out whether any
> output was produced at all after the fact.

I really wish we had never added the VIR_REALLOC_N function.
One of the best things about VIR_ALLOC/VIR_EXPAND/VIR_RESIZE
are that they remove all bugs related to use of uninitialized
memory. We really ought to try to eliminate use of VIR_REALLOC_N
in favour of the other safer functions throughout the code.

> 
> Signed-off-by: Andrea Bolognani <abologna at redhat.com>
> ---
>  src/util/vircommand.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/src/util/vircommand.c b/src/util/vircommand.c
> index d965068369..6e9e56d0c0 100644
> --- a/src/util/vircommand.c
> +++ b/src/util/vircommand.c
> @@ -2057,11 +2057,13 @@ virCommandProcessIO(virCommandPtr cmd)
>          outfd = cmd->outfd;
>          if (VIR_REALLOC_N(*cmd->outbuf, 1) < 0)
>              ret = -1;
> +        *cmd->outbuf[0] = '\0';
>      }
>      if (cmd->errbuf) {
>          errfd = cmd->errfd;
>          if (VIR_REALLOC_N(*cmd->errbuf, 1) < 0)
>              ret = -1;
> +        *cmd->errbuf[0] = '\0';

Here we don't really care about the original contents on outbuf/errbuf.
I'd probably go for making that explicit by replacing VIR_REALLOC_N
with VIR_FREE + VIR_ALLOC_N


Regards,
Daniel
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