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

[Stoiko Ivanov]

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

Signed-off-by: Stoiko Ivanov <s.ivanov at 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) {
-- 
2.20.1