Fix assorted security-grade bugs in the regex engine. All of these problems

are shared with Tcl, since it's their code to begin with, and the patches
have been copied from Tcl 8.5.0.  Problems:

CVE-2007-4769: Inadequate check on the range of backref numbers allows
crash due to out-of-bounds read.
CVE-2007-4772: Infinite loop in regex optimizer for pattern '($|^)*'.
CVE-2007-6067: Very slow optimizer cleanup for regex with a large NFA
representation, as well as crash if we encounter an out-of-memory condition
during NFA construction.

Part of the response to CVE-2007-6067 is to put a limit on the number of
states in the NFA representation of a regex.  This seems needed even though
the within-the-code problems have been corrected, since otherwise the code
could try to use very large amounts of memory for a suitably-crafted regex,
leading to potential DOS by driving the system into swap, activating a kernel
OOM killer, etc.

Although there are certainly plenty of ways to drive the system into effective
DOS with poorly-written SQL queries, these problems seem worth treating as
security issues because many applications might accept regex search patterns
from untrustworthy sources.

Thanks to Will Drewry of Google for reporting these problems.  Patches by Will
Drewry and Tom Lane.

Security: CVE-2007-4769, CVE-2007-4772, CVE-2007-6067

3 files changed, 125 insertions, 17 deletions

diff --git a/src/backend/regex/regc_color.c b/src/backend/regex/regc_color.c
index 268e072c599..87eb1e4958a 100644
--- a/src/backend/regex/regc_color.c
+++ b/src/backend/regex/regc_color.c
@@ -28,7 +28,7 @@
  * OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
  * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  *
- * $PostgreSQL: pgsql/src/backend/regex/regc_color.c,v 1.7 2007/11/15 21:14:37 momjian Exp $
+ * $PostgreSQL: pgsql/src/backend/regex/regc_color.c,v 1.8 2008/01/03 20:47:55 tgl Exp $
  *
  *
  * Note that there are some incestuous relationships between this code and
@@ -569,12 +569,9 @@ okcolors(struct nfa * nfa,
 			while ((a = cd->arcs) != NULL)
 			{
 				assert(a->co == co);
-				/* uncolorchain(cm, a); */
-				cd->arcs = a->colorchain;
+				uncolorchain(cm, a);
 				a->co = sco;
-				/* colorchain(cm, a); */
-				a->colorchain = scd->arcs;
-				scd->arcs = a;
+				colorchain(cm, a);
 			}
 			freecolor(cm, co);
 		}
@@ -604,7 +601,10 @@ colorchain(struct colormap * cm,
 {
 	struct colordesc *cd = &cm->cd[a->co];
 
+	if (cd->arcs != NULL)
+		cd->arcs->colorchainRev = a;
 	a->colorchain = cd->arcs;
+	a->colorchainRev = NULL;
 	cd->arcs = a;
 }
 
@@ -616,19 +616,22 @@ uncolorchain(struct colormap * cm,
 			 struct arc * a)
 {
 	struct colordesc *cd = &cm->cd[a->co];
-	struct arc *aa;
+	struct arc *aa = a->colorchainRev;
 
-	aa = cd->arcs;
-	if (aa == a)				/* easy case */
+	if (aa == NULL)
+	{
+		assert(cd->arcs == a);
 		cd->arcs = a->colorchain;
+	}
 	else
 	{
-		for (; aa != NULL && aa->colorchain != a; aa = aa->colorchain)
-			continue;
-		assert(aa != NULL);
+		assert(aa->colorchain == a);
 		aa->colorchain = a->colorchain;
 	}
+	if (a->colorchain != NULL)
+		a->colorchain->colorchainRev = aa;
 	a->colorchain = NULL;		/* paranoia */
+	a->colorchainRev = NULL;
 }
 
 /*
diff --git a/src/backend/regex/regc_lex.c b/src/backend/regex/regc_lex.c
index e5c83d87147..fc86ca322a9 100644
--- a/src/backend/regex/regc_lex.c
+++ b/src/backend/regex/regc_lex.c
@@ -28,7 +28,7 @@
  * OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
  * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  *
- * $PostgreSQL: pgsql/src/backend/regex/regc_lex.c,v 1.6 2007/10/22 01:02:22 tgl Exp $
+ * $PostgreSQL: pgsql/src/backend/regex/regc_lex.c,v 1.7 2008/01/03 20:47:55 tgl Exp $
  *
  */
 
@@ -846,7 +846,7 @@ lexescape(struct vars * v)
 			if (ISERR())
 				FAILW(REG_EESCAPE);
 			/* ugly heuristic (first test is "exactly 1 digit?") */
-			if (v->now - save == 0 || (int) c <= v->nsubexp)
+			if (v->now - save == 0 || ((int) c > 0 && (int) c <= v->nsubexp))
 			{
 				NOTE(REG_UBACKREF);
 				RETV(BACKREF, (chr) c);
diff --git a/src/backend/regex/regc_nfa.c b/src/backend/regex/regc_nfa.c
index fa68d021bc2..ea382df7f91 100644
--- a/src/backend/regex/regc_nfa.c
+++ b/src/backend/regex/regc_nfa.c
@@ -28,7 +28,7 @@
  * OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
  * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  *
- * $PostgreSQL: pgsql/src/backend/regex/regc_nfa.c,v 1.4 2005/10/15 02:49:24 momjian Exp $
+ * $PostgreSQL: pgsql/src/backend/regex/regc_nfa.c,v 1.5 2008/01/03 20:47:55 tgl Exp $
  *
  *
  * One or two things that technically ought to be in here
@@ -60,11 +60,12 @@ newnfa(struct vars * v,
 	nfa->nstates = 0;
 	nfa->cm = cm;
 	nfa->v = v;
+	nfa->size = 0;
 	nfa->bos[0] = nfa->bos[1] = COLORLESS;
 	nfa->eos[0] = nfa->eos[1] = COLORLESS;
+	nfa->parent = parent;		/* Precedes newfstate so parent is valid. */
 	nfa->post = newfstate(nfa, '@');	/* number 0 */
 	nfa->pre = newfstate(nfa, '>');		/* number 1 */
-	nfa->parent = parent;
 
 	nfa->init = newstate(nfa);	/* may become invalid later */
 	nfa->final = newstate(nfa);
@@ -89,6 +90,57 @@ newnfa(struct vars * v,
 }
 
 /*
+ * TooManyStates - checks if the max states exceeds the compile-time value
+ */
+static int
+TooManyStates(struct nfa *nfa)
+{
+	struct nfa *parent = nfa->parent;
+	size_t		sz = nfa->size;
+
+	while (parent != NULL)
+	{
+		sz = parent->size;
+		parent = parent->parent;
+	}
+	if (sz > REG_MAX_STATES)
+		return 1;
+	return 0;
+}
+
+/*
+ * IncrementSize - increases the tracked size of the NFA and its parents.
+ */
+static void
+IncrementSize(struct nfa *nfa)
+{
+	struct nfa *parent = nfa->parent;
+
+	nfa->size++;
+	while (parent != NULL)
+	{
+		parent->size++;
+		parent = parent->parent;
+	}
+}
+
+/*
+ * DecrementSize - decreases the tracked size of the NFA and its parents.
+ */
+static void
+DecrementSize(struct nfa *nfa)
+{
+	struct nfa *parent = nfa->parent;
+
+	nfa->size--;
+	while (parent != NULL)
+	{
+		parent->size--;
+		parent = parent->parent;
+	}
+}
+
+/*
  * freenfa - free an entire NFA
  */
 static void
@@ -122,6 +174,11 @@ newstate(struct nfa * nfa)
 {
 	struct state *s;
 
+	if (TooManyStates(nfa))
+	{
+		NERR(REG_ETOOBIG);
+		return NULL;
+	}
 	if (nfa->free != NULL)
 	{
 		s = nfa->free;
@@ -158,6 +215,8 @@ newstate(struct nfa * nfa)
 	}
 	s->prev = nfa->slast;
 	nfa->slast = s;
+	/* track the current size and the parent size */
+	IncrementSize(nfa);
 	return s;
 }
 
@@ -220,6 +279,7 @@ freestate(struct nfa * nfa,
 	s->prev = NULL;
 	s->next = nfa->free;		/* don't delete it, put it on the free list */
 	nfa->free = s;
+	DecrementSize(nfa);
 }
 
 /*
@@ -633,6 +693,8 @@ duptraverse(struct nfa * nfa,
 	for (a = s->outs; a != NULL && !NISERR(); a = a->outchain)
 	{
 		duptraverse(nfa, a->to, (struct state *) NULL);
+		if (NISERR())
+			break;
 		assert(a->to->tmp != NULL);
 		cparc(nfa, a, s->tmp, a->to->tmp);
 	}
@@ -793,6 +855,25 @@ pull(struct nfa * nfa,
 		return 1;
 	}
 
+	/*
+	 * DGP 2007-11-15: Cloning a state with a circular constraint on its list
+	 * of outs can lead to trouble [Tcl Bug 1810038], so get rid of them first.
+	 */
+	for (a = from->outs; a != NULL; a = nexta)
+	{
+		nexta = a->outchain;
+		switch (a->type)
+		{
+			case '^':
+			case '$':
+			case BEHIND:
+			case AHEAD:
+				if (from == a->to)
+					freearc(nfa, a);
+				break;
+		}
+	}
+
 	/* first, clone from state if necessary to avoid other outarcs */
 	if (from->nouts > 1)
 	{
@@ -917,6 +998,29 @@ push(struct nfa * nfa,
 		return 1;
 	}
 
+	/*
+	 * DGP 2007-11-15: Here we duplicate the same protections as appear
+	 * in pull() above to avoid troubles with cloning a state with a
+	 * circular constraint on its list of ins.  It is not clear whether
+	 * this is necessary, or is protecting against a "can't happen".
+	 * Any test case that actually leads to a freearc() call here would
+	 * be a welcome addition to the test suite.
+	 */
+	for (a = to->ins; a != NULL; a = nexta)
+	{
+		nexta = a->inchain;
+		switch (a->type)
+		{
+			case '^':
+			case '$':
+			case BEHIND:
+			case AHEAD:
+				if (a->from == to)
+					freearc(nfa, a);
+				break;
+		}
+	}
+
 	/* first, clone to state if necessary to avoid other inarcs */
 	if (to->nins > 1)
 	{
@@ -1039,7 +1143,8 @@ fixempties(struct nfa * nfa,
 	do
 	{
 		progress = 0;
-		for (s = nfa->states; s != NULL && !NISERR(); s = nexts)
+		for (s = nfa->states; s != NULL && !NISERR() &&
+				 s->no != FREESTATE; s = nexts)
 		{
 			nexts = s->next;
 			for (a = s->outs; a != NULL && !NISERR(); a = nexta)