Don't leak compiled regex(es) when an ispell cache entry is dropped.

The text search cache mechanisms assume that we can clean up
an invalidated dictionary cache entry simply by resetting the
associated long-lived memory context.  However, that does not work
for ispell affixes that make use of regular expressions, because
the regex library deals in plain old malloc.  Hence, we leaked
compiled regex(es) any time we dropped such a cache entry.  That
could quickly add up, since even a fairly trivial regex can use up
tens of kB, and a large one can eat megabytes.  Add a memory context
callback to ensure that a regex gets freed when its owning cache
entry is cleared.

Found via valgrind testing.
This problem is ancient, so back-patch to all supported branches.

Discussion: https://postgr.es/m/3816764.1616104288@sss.pgh.pa.us

diff --git a/src/backend/tsearch/spell.c b/src/backend/tsearch/spell.c
index 8aab96d3b066091b2cc5431674a8b9bcb2cd2728..756fc859acf30966ac73a457c7949fc06ee5b4e9 100644 (file)
--- a/src/backend/tsearch/spell.c
+++ b/src/backend/tsearch/spell.c
@@ -654,6 +654,17 @@ FindWord(IspellDict *Conf, const char *word, const char *affixflag, int flag)
    return 0;
 }
 
+/*
+ * Context reset/delete callback for a regular expression used in an affix
+ */
+static void
+regex_affix_deletion_callback(void *arg)
+{
+   aff_regex_struct *pregex = (aff_regex_struct *) arg;
+
+   pg_regfree(&(pregex->regex));
+}
+
 /*
  * Adds a new affix rule to the Affix field.
  *
@@ -716,6 +727,7 @@ NIAddAffix(IspellDict *Conf, const char *flag, char flagflags, const char *mask,
        int         err;
        pg_wchar   *wmask;
        char       *tmask;
+       aff_regex_struct *pregex;
 
        Affix->issimple = 0;
        Affix->isregis = 0;
@@ -729,18 +741,32 @@ NIAddAffix(IspellDict *Conf, const char *flag, char flagflags, const char *mask,
        wmask = (pg_wchar *) tmpalloc((masklen + 1) * sizeof(pg_wchar));
        wmasklen = pg_mb2wchar_with_len(tmask, wmask, masklen);
 
-       err = pg_regcomp(&(Affix->reg.regex), wmask, wmasklen,
+       /*
+        * The regex engine stores its stuff using malloc not palloc, so we
+        * must arrange to explicitly clean up the regex when the dictionary's
+        * context is cleared.  That means the regex_t has to stay in a fixed
+        * location within the context; we can't keep it directly in the AFFIX
+        * struct, since we may sort and resize the array of AFFIXes.
+        */
+       Affix->reg.pregex = pregex = palloc(sizeof(aff_regex_struct));
+
+       err = pg_regcomp(&(pregex->regex), wmask, wmasklen,
                         REG_ADVANCED | REG_NOSUB,
                         DEFAULT_COLLATION_OID);
        if (err)
        {
            char        errstr[100];
 
-           pg_regerror(err, &(Affix->reg.regex), errstr, sizeof(errstr));
+           pg_regerror(err, &(pregex->regex), errstr, sizeof(errstr));
            ereport(ERROR,
                    (errcode(ERRCODE_INVALID_REGULAR_EXPRESSION),
                     errmsg("invalid regular expression: %s", errstr)));
        }
+
+       pregex->mcallback.func = regex_affix_deletion_callback;
+       pregex->mcallback.arg = (void *) pregex;
+       MemoryContextRegisterResetCallback(CurrentMemoryContext,
+                                          &pregex->mcallback);
    }
 
    Affix->flagflags = flagflags;
@@ -2124,7 +2150,6 @@ CheckAffix(const char *word, size_t len, AFFIX *Affix, int flagflags, char *neww
    }
    else
    {
-       int         err;
        pg_wchar   *data;
        size_t      data_len;
        int         newword_len;
@@ -2134,7 +2159,8 @@ CheckAffix(const char *word, size_t len, AFFIX *Affix, int flagflags, char *neww
        data = (pg_wchar *) palloc((newword_len + 1) * sizeof(pg_wchar));
        data_len = pg_mb2wchar_with_len(newword, data, newword_len);
 
-       if (!(err = pg_regexec(&(Affix->reg.regex), data, data_len, 0, NULL, 0, NULL, 0)))
+       if (pg_regexec(&(Affix->reg.pregex->regex), data, data_len,
+                      0, NULL, 0, NULL, 0) == REG_OKAY)
        {
            pfree(data);
            return newword;

diff --git a/src/include/tsearch/dicts/spell.h b/src/include/tsearch/dicts/spell.h
index 7bb29376136cdbd2226e0f1fbf648c51b238cfe8..9ec08bea7d077958c8e90f1a247e7f6fac8f88be 100644 (file)
--- a/src/include/tsearch/dicts/spell.h
+++ b/src/include/tsearch/dicts/spell.h
@@ -81,6 +81,17 @@ typedef struct spell_struct
 
 #define SPELLHDRSZ (offsetof(SPELL, word))
 
+/*
+ * If an affix uses a regex, we have to store that separately in a struct
+ * that won't move around when arrays of affixes are enlarged or sorted.
+ * This is so that it can be found to be cleaned up at context destruction.
+ */
+typedef struct aff_regex_struct
+{
+   regex_t     regex;
+   MemoryContextCallback mcallback;
+} aff_regex_struct;
+
 /*
  * Represents an entry in an affix list.
  */
@@ -97,7 +108,7 @@ typedef struct aff_struct
    char       *repl;
    union
    {
-       regex_t     regex;
+       aff_regex_struct *pregex;
        Regis       regis;
    }           reg;
 } AFFIX;