Re: [pve-devel] [PATCH common] run_command: untaint end of buffer

[Thomas Lamprecht <t.lamprecht@proxmox.com>]

On 22.06.21 16:28, Stoiko Ivanov wrote:
> The performance improvements added in
> cb9db10c1a9855cf40ff13e81f9dd97d6a9b2698 changed the output handling
> to not remove the taintedness (see perlsec (1)) of the complete output
> anymore.
> 
> This results in a few bugs which show up every now and then, and are
> usually quite tedious to hunt down - usually they only occur when
> run via GUI (since pveproxy/pvedaemon run in taint-mode, whereas our
> CLI utilities usually do not) - see for example pve-storage commit
> 609f117ff24d2cff6b155e1d4b1175ceebe5bd7b
> 
> or more recently the report in our community-forum:
> https://forum.proxmox.com/threads/cannot-clone-vm-or-move-disk-with-more-than-13-snapshots.89628/
> (the magic number of 13 snapshots is the point where the output of
> `qemu-img info --output=json` grows to more than 4k)
> 
> Given the doubtful security benefit of having to untaint output, only
> if it does not end in new-line or if it is longer than 4k (we read
> the output in 4k chunks) simply untaint the output unconditionally.
> 
> Tested with the reproducer from the forum-thread
> 

this long message nowhere talks about what the actual issue is, can we rather
fix that in the clone call?

> Signed-off-by: Stoiko Ivanov <s.ivanov@proxmox.com>
> ---
> Huge thanks to Dominik who pointed me in the right direction, after I
> spend far more time than I'm proud to admit in the JSON::XS source,
> perlsec(1), perlguts(1) and the surprisingly unhelpful output of
> debugperl -Du
> 
>  src/PVE/Tools.pm | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/src/PVE/Tools.pm b/src/PVE/Tools.pm
> index 8946e93..eb140ae 100644
> --- a/src/PVE/Tools.pm
> +++ b/src/PVE/Tools.pm
> @@ -516,7 +516,7 @@ sub run_command {
>  				&$outfunc($line) if $outfunc;
>  				&$logfunc($line) if $logfunc;
>  			    }
> -			    $outlog .= $buf;
> +			    ($outlog) .= ($buf =~ /(.*)/); #untaint
>  			};
>  			my $err = $@;
>  			if ($err) {
> @@ -537,7 +537,7 @@ sub run_command {
>  				&$errfunc($line) if $errfunc;
>  				&$logfunc($line) if $logfunc;
>  			    }
> -			    $errlog .= $buf;
> +			    ($errlog) .= ($buf =~ /(.*)/); #untaint
>  			};
>  			my $err = $@;
>  			if ($err) {
>