From c56b2aa6efd1c0d090a9747a8220bf5110e9f9fd Mon Sep 17 00:00:00 2001 From: Tom Lane Date: Fri, 2 Oct 2015 13:30:42 -0400 Subject: [PATCH] Docs: add disclaimer about hazards of using regexps from untrusted sources. It's not terribly hard to devise regular expressions that take large amounts of time and/or memory to process. Recent testing by Greg Stark has also shown that machines with small stack limits can be driven to stack overflow by suitably crafted regexps. While we intend to fix these things as much as possible, it's probably impossible to eliminate slow-execution cases altogether. In any case we don't want to treat such things as security issues. The history of that code should already discourage prudent DBAs from allowing execution of regexp patterns coming from possibly-hostile sources, but it seems like a good idea to warn about the hazard explicitly. Currently, similar_escape() allows access to enough of the underlying regexp behavior that the warning has to apply to SIMILAR TO as well. We might be able to make it safer if we tightened things up to allow only SQL-mandated capabilities in SIMILAR TO; but that would be a subtly non-backwards-compatible change, so it requires discussion and probably could not be back-patched. Per discussion among pgsql-security list. --- doc/src/sgml/func.sgml | 22 ++++++++++++++++++++++ 1 file changed, 22 insertions(+) diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml index 26f863b326..262f5eea9f 100644 --- a/doc/src/sgml/func.sgml +++ b/doc/src/sgml/func.sgml @@ -3600,6 +3600,28 @@ cast(-44 as bit(12)) 111111010100 + + + While most regular-expression searches can be executed very quickly, + regular expressions can be contrived that take arbitrary amounts of + time and memory to process. Be wary of accepting regular-expression + search patterns from hostile sources. If you must do so, it is + advisable to impose a statement timeout. + + + + Searches using SIMILAR TO patterns have the same + security hazards, since SIMILAR TO provides many + of the same capabilities as POSIX-style regular + expressions. + + + + LIKE searches, being much simpler than the other + two options, are safer to use with possibly-hostile pattern sources. + + + <function>LIKE</function>