48789c5d23
It's possible to construct regular expressions that contain loops of constraint arcs (that is, ^ $ AHEAD BEHIND or LACON arcs). There's no use in fully traversing such a loop at execution, since you'd just end up in the same NFA state without having consumed any input. Worse, such a loop leads to infinite looping in the pullback/pushfwd stage of compilation, because we keep pushing or pulling the same constraints around the loop in a vain attempt to move them to the pre or post state. Such looping was previously recognized in CVE-2007-4772; but the fix only handled the case of trivial single-state loops (that is, a constraint arc leading back to its source state) ... and not only that, it was incorrect even for that case, because it broke the admittedly-not-very-clearly-stated API contract of the pull() and push() subroutines. The first two regression test cases added by this commit exhibit patterns that result in assertion failures because of that (though there seem to be no ill effects in non-assert builds). The other new test cases exhibit multi-state constraint loops; in an unpatched build they will run until the NFA state-count limit is exceeded. To fix, remove the code added for CVE-2007-4772, and instead create a general-purpose constraint-loop-breaking phase of regex compilation that executes before we do pullback/pushfwd. Since we never need to traverse a constraint loop fully, we can just break the loop at any chosen spot, if we add clone states that can replicate any sequence of arc transitions that would've traversed just part of the loop. Also add some commentary clarifying why we have to have all these machinations in the first place. This class of problems has been known for some time --- we had a report from Marc Mamin about two years ago, for example, and there are related complaints in the Tcl bug tracker. I had discussed a fix of this kind off-list with Henry Spencer, but didn't get around to doing something about it until the issue was rediscovered by Greg Stark recently. Back-patch to all supported branches. |
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README
PostgreSQL Database Management System ===================================== This directory contains the source code distribution of the PostgreSQL database management system. PostgreSQL is an advanced object-relational database management system that supports an extended subset of the SQL standard, including transactions, foreign keys, subqueries, triggers, user-defined types and functions. This distribution also contains C language bindings. PostgreSQL has many language interfaces, many of which are listed here: http://www.postgresql.org/download See the file INSTALL for instructions on how to build and install PostgreSQL. That file also lists supported operating systems and hardware platforms and contains information regarding any other software packages that are required to build or run the PostgreSQL system. Copyright and license information can be found in the file COPYRIGHT. A comprehensive documentation set is included in this distribution; it can be read as described in the installation instructions. The latest version of this software may be obtained at http://www.postgresql.org/download/. For more information look at our web site located at http://www.postgresql.org/.