Edit report at https://bugs.php.net/bug.php?id=61706&edit=1
ID: 61706
Comment by: phpbugs at personal dot formauri dot es
Reported by: phpbugs at personal dot formauri dot es
Summary: escapeshellarg behaves inconsistently depending on
shell
Status: Open
Type: Bug
Package: Program Execution
Operating System: Linux, Unix, maybe OSX, NOT msw
PHP Version: 5.4Git-2012-04-12 (Git)
Block user comment: N
Private report: N
New Comment:
For extra background, see
http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=550399
Unlike what I thought at first, it seems to affect the shell's built-in echo
command specifically. As noted in that bug, it also affects shells other than
dash, including posh and mksh. I've had the problem with zsh as well. And as
noted in that bug, dash is the default shell in many systems, and also in
Ubuntu (see https://bugs.launchpad.net/ubuntu/+source/dash/+bug/259671 ).
Debian also offers to install posh as the default /bin/sh. The consensus seems
to be that that is not a bug in the shell, because the result of using
backslashes in the shell's builtin echo is implementation-defined, and
therefore it's PHP's responsibility to escape them properly, e.g. in the
suggested way.
On a different topic, one advantage of using the method of switching mode
depending on the runs of should-be-escaped/should-not-be-escaped characters, as
in the PHP example function shown above, is that the temporary storage
requirement is reduced from 4n+2 as is now, or ~4 times the length, to
ceil(5n/2), or ~2.5 times the length. That's because the worst case for the
current behavior is a sequence of single-quotes which is written as
''\'''\'''\''...'\''' and the worst case for the proposed behaviour is
alternating escaped/non-escaped characters as in 'x'\\'x'\\'x'\\...'x',
therefore every 2 characters are turned into 5 with possibly an extra character
at the end.
Previous Comments:
------------------------------------------------------------------------
[2012-04-13 00:51:55] zhanglijiu at gmail dot com
My result is \\
my system is Mac OS
SHould be bash
------------------------------------------------------------------------
[2012-04-12 22:22:04] phpbugs at personal dot formauri dot es
Description:
------------
Depending on the shell, for shell internal commands the backslashes within
single quotes are interpreted as escapes or are used verbatim. For example, in
bash and in busybox:
$ echo '\\'
\\
But in dash:
$ echo '\\'
\
dash is frequently set as the default /bin/sh so this is a problem. More so
since some programs need to get their input from stdin and therefore they need
the use of 'echo' for input not coming from a file or being input from the
console.
To work around the backslash inconsistency among shells, backslashes should
receive special treatment as quotes do, e.g. translate \ to '\\'.
I was tempted of sending this as a security issue, but the scenarios where
security could be in risk are too improbable for it to be a serious security
concern.
Ideally though, no unnecessary quotes should be used in the output string, e.g.
escapeshellarg should convert '''abc\\'\ into \'\'\''abc'\\\\\'\\. Currently it
converts '''abc\\'\ into ''\'''\'''\''abc\\'\''\' which exhibits the bug and is
unnecessarily large.
For backwards compatibility, maybe an extra argument should be added to also
quote backslashes and use a new method of quoting.
Here is a PHP function that implements the suggestions here, using strspn and
strcspn to grab the longest spans that it can "eat" at a time of each kind
(characters to escape / characters not to escape):
http://www.formauri.es/personal/pgimeno/temp/sh_escape.phps (includes test
suite).
Test script:
---------------
<?php
$backslash = "\\";
system('echo ' . escapeshellarg($backslash . $backslash));
?>
Expected result:
----------------
No matter the shell:
\\
Actual result:
--------------
If your /bin/sh is dash:
\
If your /bin/sh is busybox:
\\
Other shells: ??
------------------------------------------------------------------------
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Edit this bug report at https://bugs.php.net/bug.php?id=61706&edit=1
