From b63fc28776c5d2efdb4de326ad0f0b5b88f82220 Mon Sep 17 00:00:00 2001 From: Tom Lane Date: Fri, 2 Oct 2015 14:51:58 -0400 Subject: [PATCH] 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. --- src/backend/regex/regc_nfa.c | 68 ++++++++++++++++++++++++++++++++---- src/backend/regex/regcomp.c | 34 ++++++++++++++++-- src/backend/regex/rege_dfa.c | 7 ++++ src/backend/regex/regexec.c | 3 ++ src/backend/tcop/postgres.c | 39 ++++++++++++--------- src/include/miscadmin.h | 1 + src/include/regex/regguts.h | 4 +++ 7 files changed, 129 insertions(+), 27 deletions(-) diff --git a/src/backend/regex/regc_nfa.c b/src/backend/regex/regc_nfa.c index e474e48c28..50a762ed7a 100644 --- 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 d137ac0d3d..62f6359e34 100644 --- 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 const 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 a9305dd7cc..a37e4b0ef9 100644 --- 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 d18672c7c7..8a21f2cb78 100644 --- 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 d1f43c5c8a..aee13aec75 100644 --- a/src/backend/tcop/postgres.c +++ b/src/backend/tcop/postgres.c @@ -3081,15 +3081,32 @@ 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; @@ -3115,14 +3132,7 @@ 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 @@ -3137,15 +3147,10 @@ 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 80ac7329dc..ff695aae27 100644 --- a/src/include/miscadmin.h +++ b/src/include/miscadmin.h @@ -268,6 +268,7 @@ 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 fccaf298bf..3277752355 100644 --- a/src/include/regex/regguts.h +++ b/src/include/regex/regguts.h @@ -449,11 +449,15 @@ 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 * -- 2.40.0