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Tom Lane 0889e1857f Fix regular-expression compiler to handle loops of constraint arcs. ... 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.		10 years ago
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backend	Fix regular-expression compiler to handle loops of constraint arcs.	10 years ago
bin	-- email subject limit -----------------------------------------	10 years ago
common	pgindent run for 9.5	11 years ago
include	Remove cautions about using volatile from spin.h.	10 years ago
interfaces	Translation updates	10 years ago
makefiles	Link $(WIN32RES) into single-file modules only when PGFILEDESC is set.	11 years ago
pl	Translation updates	10 years ago
port	Redesign tablesample method API, and do extensive code review.	11 years ago
template	AIX: Test the -qlonglong option before use.	11 years ago
test	Fix regular-expression compiler to handle loops of constraint arcs.	10 years ago
timezone	Update time zone data files to tzdata release 2015g.	10 years ago
tools	Rework the way multixact truncations work.	10 years ago
tutorial	Remove no-longer-required function declarations.	11 years ago
.gitignore	…
DEVELOPERS	…
Makefile	…
Makefile.global.in	Make prove_installcheck remove the old log directory, if any.	10 years ago
Makefile.shlib	AIX: Link TRANSFORM modules with their dependencies.	11 years ago
bcc32.mak	…
nls-global.mk	…
win32.mak	…