Add recursion depth protections to regular expression matching.

Some of the functions in regex compilation and execution recurse, and
therefore could in principle be driven to stack overflow.  The Tcl crew
has seen this happen in practice in duptraverse(), though their fix was
to put in a hard-wired limit on the number of recursive levels, which is
not too appetizing --- fortunately, we have enough infrastructure to check
the actually available stack.  Greg Stark has also seen it in other places
while fuzz testing on a machine with limited stack space.  Let's put guards
in to prevent crashes in all these places.

Since the regex code would leak memory if we simply threw elog(ERROR),
we have to introduce an API that checks for stack depth without throwing
such an error.  Fortunately that's not difficult.

diff --git a/src/backend/regex/regc_nfa.c b/src/backend/regex/regc_nfa.c
index e474e48c28c97a328a8fa0a2083d9e55e757bdb3..50a762ed7ac0b959fa5405a8dbafffbdb7db4811 100644 (file)
--- a/src/backend/regex/regc_nfa.c
+++ b/src/backend/regex/regc_nfa.c
@@ -683,6 +683,8 @@ delsub(struct nfa * nfa,
    rp->tmp = rp;               /* mark end */
 
    deltraverse(nfa, lp, lp);
+   if (NISERR())
+       return;                 /* asserts might not hold after failure */
    assert(lp->nouts == 0 && rp->nins == 0);    /* did the job */
    assert(lp->no != FREESTATE && rp->no != FREESTATE); /* no more */
 
@@ -702,6 +704,13 @@ deltraverse(struct nfa * nfa,
    struct arc *a;
    struct state *to;
 
+   /* Since this is recursive, it could be driven to stack overflow */
+   if (STACK_TOO_DEEP(nfa->v->re))
+   {
+       NERR(REG_ETOOBIG);
+       return;
+   }
+
    if (s->nouts == 0)
        return;                 /* nothing to do */
    if (s->tmp != NULL)
@@ -713,6 +722,8 @@ deltraverse(struct nfa * nfa,
    {
        to = a->to;
        deltraverse(nfa, leftend, to);
+       if (NISERR())
+           return;             /* asserts might not hold after failure */
        assert(to->nouts == 0 || to->tmp != NULL);
        freearc(nfa, a);
        if (to->nins == 0 && to->tmp == NULL)
@@ -767,6 +778,13 @@ duptraverse(struct nfa * nfa,
 {
    struct arc *a;
 
+   /* Since this is recursive, it could be driven to stack overflow */
+   if (STACK_TOO_DEEP(nfa->v->re))
+   {
+       NERR(REG_ETOOBIG);
+       return;
+   }
+
    if (s->tmp != NULL)
        return;                 /* already done */
 
@@ -796,6 +814,13 @@ cleartraverse(struct nfa * nfa,
 {
    struct arc *a;
 
+   /* Since this is recursive, it could be driven to stack overflow */
+   if (STACK_TOO_DEEP(nfa->v->re))
+   {
+       NERR(REG_ETOOBIG);
+       return;
+   }
+
    if (s->tmp == NULL)
        return;
    s->tmp = NULL;
@@ -1284,7 +1309,7 @@ fixempties(struct nfa * nfa,
     */
    for (s = nfa->states; s != NULL && !NISERR(); s = s->next)
    {
-       for (s2 = emptyreachable(s, s); s2 != s && !NISERR(); s2 = nexts)
+       for (s2 = emptyreachable(nfa, s, s); s2 != s && !NISERR(); s2 = nexts)
        {
            /*
             * If s2 is doomed, we decide that (1) we will always push arcs
@@ -1342,19 +1367,28 @@ fixempties(struct nfa * nfa,
  *
  * The maximum recursion depth here is equal to the length of the longest
  * loop-free chain of EMPTY arcs, which is surely no more than the size of
- * the NFA, and in practice will be a lot less than that.
+ * the NFA ... but that could still be enough to cause trouble.
  */
 static struct state *
-emptyreachable(struct state * s, struct state * lastfound)
+emptyreachable(struct nfa * nfa,
+              struct state * s,
+              struct state * lastfound)
 {
    struct arc *a;
 
+   /* Since this is recursive, it could be driven to stack overflow */
+   if (STACK_TOO_DEEP(nfa->v->re))
+   {
+       NERR(REG_ETOOBIG);
+       return lastfound;
+   }
+
    s->tmp = lastfound;
    lastfound = s;
    for (a = s->outs; a != NULL; a = a->outchain)
    {
        if (a->type == EMPTY && a->to->tmp == NULL)
-           lastfound = emptyreachable(a->to, lastfound);
+           lastfound = emptyreachable(nfa, a->to, lastfound);
    }
    return lastfound;
 }
@@ -1433,19 +1467,22 @@ cleanup(struct nfa * nfa)
    struct state *nexts;
    int         n;
 
+   if (NISERR())
+       return;
+
    /* clear out unreachable or dead-end states */
    /* use pre to mark reachable, then post to mark can-reach-post */
    markreachable(nfa, nfa->pre, (struct state *) NULL, nfa->pre);
    markcanreach(nfa, nfa->post, nfa->pre, nfa->post);
-   for (s = nfa->states; s != NULL; s = nexts)
+   for (s = nfa->states; s != NULL && !NISERR(); s = nexts)
    {
        nexts = s->next;
        if (s->tmp != nfa->post && !s->flag)
            dropstate(nfa, s);
    }
-   assert(nfa->post->nins == 0 || nfa->post->tmp == nfa->post);
+   assert(NISERR() || nfa->post->nins == 0 || nfa->post->tmp == nfa->post);
    cleartraverse(nfa, nfa->pre);
-   assert(nfa->post->nins == 0 || nfa->post->tmp == NULL);
+   assert(NISERR() || nfa->post->nins == 0 || nfa->post->tmp == NULL);
    /* the nins==0 (final unreachable) case will be caught later */
 
    /* renumber surviving states */
@@ -1466,6 +1503,13 @@ markreachable(struct nfa * nfa,
 {
    struct arc *a;
 
+   /* Since this is recursive, it could be driven to stack overflow */
+   if (STACK_TOO_DEEP(nfa->v->re))
+   {
+       NERR(REG_ETOOBIG);
+       return;
+   }
+
    if (s->tmp != okay)
        return;
    s->tmp = mark;
@@ -1485,6 +1529,13 @@ markcanreach(struct nfa * nfa,
 {
    struct arc *a;
 
+   /* Since this is recursive, it could be driven to stack overflow */
+   if (STACK_TOO_DEEP(nfa->v->re))
+   {
+       NERR(REG_ETOOBIG);
+       return;
+   }
+
    if (s->tmp != okay)
        return;
    s->tmp = mark;
@@ -1502,6 +1553,9 @@ analyze(struct nfa * nfa)
    struct arc *a;
    struct arc *aa;
 
+   if (NISERR())
+       return 0;
+
    if (nfa->pre->outs == NULL)
        return REG_UIMPOSSIBLE;
    for (a = nfa->pre->outs; a != NULL; a = a->outchain)

diff --git a/src/backend/regex/regcomp.c b/src/backend/regex/regcomp.c
index 3e2440ccc336e7d8c4b48bd20caa1f584155396f..570d12a89c4a5d983c1add738d7f4753a61a8098 100644 (file)
--- a/src/backend/regex/regcomp.c
+++ b/src/backend/regex/regcomp.c
@@ -34,7 +34,7 @@
 
 #include "regex/regguts.h"
 
-#include "miscadmin.h"         /* needed by rcancelrequested() */
+#include "miscadmin.h"         /* needed by rcancelrequested/rstacktoodeep */
 
 /*
  * forward declarations, up here so forward datatypes etc. are defined early
@@ -70,6 +70,7 @@ static int    newlacon(struct vars *, struct state *, struct state *, int);
 static void freelacons(struct subre *, int);
 static void rfree(regex_t *);
 static int rcancelrequested(void);
+static int rstacktoodeep(void);
 
 #ifdef REG_DEBUG
 static void dump(regex_t *, FILE *);
@@ -152,7 +153,7 @@ static int  push(struct nfa *, struct arc *);
 #define COMPATIBLE 3           /* compatible but not satisfied yet */
 static int combine(struct arc *, struct arc *);
 static void fixempties(struct nfa *, FILE *);
-static struct state *emptyreachable(struct state *, struct state *);
+static struct state *emptyreachable(struct nfa *, struct state *, struct state *);
 static void replaceempty(struct nfa *, struct state *, struct state *);
 static void cleanup(struct nfa *);
 static void markreachable(struct nfa *, struct state *, struct state *, struct state *);
@@ -279,7 +280,8 @@ struct vars
 /* static function list */
 static struct fns functions = {
    rfree,                      /* regfree insides */
-   rcancelrequested            /* check for cancel request */
+   rcancelrequested,           /* check for cancel request */
+   rstacktoodeep               /* check for stack getting dangerously deep */
 };
 
 
@@ -1626,6 +1628,16 @@ subre(struct vars * v,
 {
    struct subre *ret = v->treefree;
 
+   /*
+    * Checking for stack overflow here is sufficient to protect parse() and
+    * its recursive subroutines.
+    */
+   if (STACK_TOO_DEEP(v->re))
+   {
+       ERR(REG_ETOOBIG);
+       return NULL;
+   }
+
    if (ret != NULL)
        v->treefree = ret->left;
    else
@@ -1938,6 +1950,22 @@ rcancelrequested(void)
    return InterruptPending && (QueryCancelPending || ProcDiePending);
 }
 
+/*
+ * rstacktoodeep - check for stack getting dangerously deep
+ *
+ * Return nonzero to fail the operation with error code REG_ETOOBIG,
+ * zero to keep going
+ *
+ * The current implementation is Postgres-specific.  If we ever get around
+ * to splitting the regex code out as a standalone library, there will need
+ * to be some API to let applications define a callback function for this.
+ */
+static int
+rstacktoodeep(void)
+{
+   return stack_is_too_deep();
+}
+
 #ifdef REG_DEBUG
 
 /*

diff --git a/src/backend/regex/rege_dfa.c b/src/backend/regex/rege_dfa.c
index a9305dd7ccd231e8af3ecf24b31be6991fa22b26..a37e4b0ef96660c47b01c9fe32e10a0b39d511b9 100644 (file)
--- a/src/backend/regex/rege_dfa.c
+++ b/src/backend/regex/rege_dfa.c
@@ -627,6 +627,13 @@ lacon(struct vars * v,
    struct smalldfa sd;
    chr        *end;
 
+   /* Since this is recursive, it could be driven to stack overflow */
+   if (STACK_TOO_DEEP(v->re))
+   {
+       ERR(REG_ETOOBIG);
+       return 0;
+   }
+
    n = co - pcnfa->ncolors;
    assert(n < v->g->nlacons && v->g->lacons != NULL);
    FDEBUG(("=== testing lacon %d\n", n));

diff --git a/src/backend/regex/regexec.c b/src/backend/regex/regexec.c
index 66847d4adfa338bf66b7c712eca9c32204adf1e6..45c3a579c755b9d2f16405159a85fc3c522f143c 100644 (file)
--- a/src/backend/regex/regexec.c
+++ b/src/backend/regex/regexec.c
@@ -624,6 +624,9 @@ cdissect(struct vars * v,
    /* handy place to check for operation cancel */
    if (CANCEL_REQUESTED(v->re))
        return REG_CANCEL;
+   /* ... and stack overrun */
+   if (STACK_TOO_DEEP(v->re))
+       return REG_ETOOBIG;
 
    switch (t->op)
    {

diff --git a/src/backend/tcop/postgres.c b/src/backend/tcop/postgres.c
index 5d70a9dd13e44e6ab2186976d73873c66e710721..225ebd18512ce1fb8a82122fadc45ea2dbfa98cb 100644 (file)
--- a/src/backend/tcop/postgres.c
+++ b/src/backend/tcop/postgres.c
@@ -3097,15 +3097,32 @@ restore_stack_base(pg_stack_base_t base)
 }
 
 /*
- * check_stack_depth: check for excessively deep recursion
+ * check_stack_depth/stack_is_too_deep: check for excessively deep recursion
  *
  * This should be called someplace in any recursive routine that might possibly
  * recurse deep enough to overflow the stack.  Most Unixen treat stack
  * overflow as an unrecoverable SIGSEGV, so we want to error out ourselves
  * before hitting the hardware limit.
+ *
+ * check_stack_depth() just throws an error summarily.  stack_is_too_deep()
+ * can be used by code that wants to handle the error condition itself.
  */
 void
 check_stack_depth(void)
+{
+   if (stack_is_too_deep())
+   {
+       ereport(ERROR,
+               (errcode(ERRCODE_STATEMENT_TOO_COMPLEX),
+                errmsg("stack depth limit exceeded"),
+                errhint("Increase the configuration parameter \"max_stack_depth\" (currently %dkB), "
+             "after ensuring the platform's stack depth limit is adequate.",
+                        max_stack_depth)));
+   }
+}
+
+bool
+stack_is_too_deep(void)
 {
    char        stack_top_loc;
    long        stack_depth;
@@ -3131,14 +3148,7 @@ check_stack_depth(void)
     */
    if (stack_depth > max_stack_depth_bytes &&
        stack_base_ptr != NULL)
-   {
-       ereport(ERROR,
-               (errcode(ERRCODE_STATEMENT_TOO_COMPLEX),
-                errmsg("stack depth limit exceeded"),
-                errhint("Increase the configuration parameter \"max_stack_depth\" (currently %dkB), "
-             "after ensuring the platform's stack depth limit is adequate.",
-                        max_stack_depth)));
-   }
+       return true;
 
    /*
     * On IA64 there is a separate "register" stack that requires its own
@@ -3153,15 +3163,10 @@ check_stack_depth(void)
 
    if (stack_depth > max_stack_depth_bytes &&
        register_stack_base_ptr != NULL)
-   {
-       ereport(ERROR,
-               (errcode(ERRCODE_STATEMENT_TOO_COMPLEX),
-                errmsg("stack depth limit exceeded"),
-                errhint("Increase the configuration parameter \"max_stack_depth\" (currently %dkB), "
-             "after ensuring the platform's stack depth limit is adequate.",
-                        max_stack_depth)));
-   }
+       return true;
 #endif   /* IA64 */
+
+   return false;
 }
 
 /* GUC check hook for max_stack_depth */

diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 51bb0642dc5d557c9338fe43c4713e5f0d0fa816..036d004cd6ca1573db679f657cbafb2cdd6e4aff 100644 (file)
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -274,6 +274,7 @@ typedef char *pg_stack_base_t;
 extern pg_stack_base_t set_stack_base(void);
 extern void restore_stack_base(pg_stack_base_t base);
 extern void check_stack_depth(void);
+extern bool stack_is_too_deep(void);
 
 /* in tcop/utility.c */
 extern void PreventCommandIfReadOnly(const char *cmdname);

diff --git a/src/include/regex/regguts.h b/src/include/regex/regguts.h
index db3a89d785a64e99d4fdddd25c0996c24014f9bf..2d9349ee317a49cf1866046486f79722ba60d46c 100644 (file)
--- a/src/include/regex/regguts.h
+++ b/src/include/regex/regguts.h
@@ -447,11 +447,15 @@ struct fns
 {
    void        FUNCPTR(free, (regex_t *));
    int         FUNCPTR(cancel_requested, (void));
+   int         FUNCPTR(stack_too_deep, (void));
 };
 
 #define CANCEL_REQUESTED(re)  \
    ((*((struct fns *) (re)->re_fns)->cancel_requested) ())
 
+#define STACK_TOO_DEEP(re) \
+   ((*((struct fns *) (re)->re_fns)->stack_too_deep) ())
+
 
 /*
  * the insides of a regex_t, hidden behind a void *