[drupal-devel] [bug] user_access returns invalid data

javanaut drupal-devel at drupal.org
Fri Feb 4 14:25:44 UTC 2005

 Project:      Drupal
 Version:      4.5.0
 Component:    user.module
 Category:     bug reports
 Priority:     critical
 Assigned to:  javanaut
 Reported by:  javanaut
 Updated by:   javanaut
 Status:       patch

The security flaw that this fixes is where strstr finds too man positive
results.  Example:
module A has permission "type A create content" (Allowed for role)
module B has permission "create content" (Disallowed for role)
user_access("create content") is run for module B and returns
non-FALSE, non-null results, even though the role is disallowed. 
Avoiding this would require a permission naming convention such that no
permission were a substring of another.


Previous comments:

February 3, 2005 - 15:32 : javanaut

Attachment: http://drupal.org/files/issues/user_access_bug.patch (473 bytes)

The user_access function in user.module returns the results of the
*strstr()* function, which returns a string, not a Boolean like the
documentation suggests.  This was screwing things up for me since
flexinode relies on user_access for it's node_access('create'..)
The attached patch uses strpos instead of strstr.  It was created from
a 4.5 codebase, but I noticed that the same issue is in HEAD as well. 
I'm using it on my dev site, and node_access('create'..) calls are now
working properly and nothing I'm using seems to have any problems with


February 3, 2005 - 17:20 : Anonymous

+  return strpos($perm[$account->uid], "$string, ") !== FALSE ? TRUE :
could be written more simply as
+  return strpos($perm[$account->uid], "$string, ") !== FALSE;
Keep in mind it's also possible to type-cast the result of strstr to a
boolean value (i.e. return (bool) strstr($perm[$account->uid],
"$string, ");)... I am unsure as to whether strstr or strpos would be
faster... perhaps a quick benchmark could answer the question of which
we should use.


February 3, 2005 - 19:24 : javanaut

Heh, after posting that, I realized what I had done, but never got back
around to simplifying it.  Good eye.


February 3, 2005 - 23:25 : tangent

The PHP docs claim that strpos is faster and less memory intensive than
For what it's worth, the second statement below does not seem more
simple or readable than the first to me though it's hard to say if
casting an int as a boolean is more or less performant than performing
a logical comparison.
return strpos($perm[$account->uid], "$string, ") !== FALSE ? TRUE :
return (bool) strpos($perm[$account->uid], "$string, ") !== FALSE;

View: http://drupal.org/node/16705
Edit: http://drupal.org/project/comments/add/16705

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