ID: 30698
User updated by: php at richardneill dot org
Reported By: php at richardneill dot org
Status: Bogus
Bug Type: Documentation problem
Operating System: Linux
PHP Version: 4.3.9
New Comment:
Sorry if I'm being daft here, but my reading of the documentation is
that both single and double quotes are always escaped.
However, as per your post:
modify('\\1') ....resulting in
single quote ', a double quote \", and a backslash\
modify("\\1") ... resulting in
single quote \', a double quote ", and a backslash\
My reading of this is that the first time (single quoted
backreference), only the double quotes, but not the single quotes are
escaped. The reverse is true the second time.
Perhaps a better sentence for the documentation would be
"Single XOR double quotes are escaped by backslashes in substituted
backreferences"
I apologise for getting them the wrong way round earlier!
My main point isn't that it works wrongly, but that the behaviour may
be confusing, and that especially for less wizardly programmers such as
myself, it would be helpful if it were spelled out a little more. I made
a mistake, which I was lucky to catch before I received an SQL injection
attack, and that's why I hope that other people will at least have more
warning before they err similarly.
Best wishes,
Richard
Previous Comments:
------------------------------------------------------------------------
[2005-04-05 19:28:03] [EMAIL PROTECTED]
The code is escaped, then executed. Read again the post from 5 Apr
3:46pm CEST.
------------------------------------------------------------------------
[2005-04-05 17:47:04] php at richardneill dot org
Sorry - I'm not thinking clearly today - need more coffee! Anyway, the
parts (ii) in my previous comment are complete nonsense, but the parts
(i) are true.
I still think that the documentation is wrong: it reads:
"Single AND double quotes are escaped by backslashes in substituted
backreferences"
whereas it should read:
"In single-quoted backreferences, single-quotes are escaped by
backslashes; double quotes are not escaped". The reverse applies for
double-quoted backreferences.
------------------
I also think that some sort of warning is important here (even if it's
just a link to another page). This is necessary because a double
escaped quote becomes an SQL injection issue. Eg:
User writes:
Here's a test.
After magic quoting:
Here\'s a test.
After preg_replace using ("\\1")
Here\\'s a test
SQL:
$sql="UPDATE table SET value='$input'";
Database query is:
UPDATE table SET value='Here\\'s a test'
which is parsed as literal \ followed by unescaped '
Which will fail.
Thus the user thinks that they are always safe because of magic-quotes,
but in fact they are NOT.
------------------------------------------------------------------------
[2005-04-05 16:59:43] [EMAIL PROTECTED]
Unescaped quotes doesn't cause parse error thanks to escaping provided
by /e.
<?php
echo preg_replace('~.*~e', '"\\0"', '"'); // ", no parse error
?>
I'm against messing this part with magic_qutes and SQL injection
issues.
------------------------------------------------------------------------
[2005-04-05 16:47:43] php at richardneill dot org
I don't think this is exactly bogus, since I think the documentation is
not clear. The documentation for /e says just:
--------------------
If this modifier is set, preg_replace() does normal substitution of
backreferences in the replacement string, evaluates it as PHP code, and
uses the result for replacing the search string. Single and double
quotes are escaped by backslashes in substituted backreferences.
----------------------
Given that this is a really awkward potential gotcha, especially when
it interacts with PHP's magic quotes and SQL, I think it is worth
stressing that:
a)If the backreference is single quoted, eg:
('\\1')
then
i)Double quotes will become escaped by \
ii)Unescaped single quotes will cause a parse error.
b)If the backreference is double quoted, eg:
("\\1")
then
i)single quotes will become escaped by \
ii)Unescaped double quotes will cause a parse error.
c)If the source is user-input which has had magic-quotes applied, then
quotes of type (i) will end up doubly escaped causing an SQL error,
and one of the escapes must be removed
quotes of type (ii) will lose their magic quoting, and need to have
the escape restored.
------------------------------------------------------------------------
[2005-04-05 15:46:35] [EMAIL PROTECTED]
It works as expected and documented:
modify('\\1') is translated to modify('single quote \', a double quote
\", and a backslash\\') resulting in
single quote ', a double quote \", and a backslash\
---
modify("\\1") is translated to modify("single quote \', a double quote
\", and a backslash\\") resulting in
single quote \', a double quote ", and a backslash\
------------------------------------------------------------------------
The remainder of the comments for this report are too long. To view
the rest of the comments, please view the bug report online at
http://bugs.php.net/30698
--
Edit this bug report at http://bugs.php.net/?id=30698&edit=1
