Fix (some of) pltcl memory usage

As reported by Bill Parker, PL/Tcl did not validate some malloc() calls
against NULL return.  Fix by using palloc() in a new long-lived memory
context instead.  This allows us to simplify error handling too, by
simply deleting the memory context instead of doing retail frees.

There's still a lot that could be done to improve PL/Tcl's memory
handling ...

This is pretty ancient, so backpatch all the way back.

Author: Michael Paquier and Álvaro Herrera
Discussion: https://www.postgresql.org/message-id/CAFrbyQwyLDYXfBOhPfoBGqnvuZO_Y90YgqFM11T2jvnxjLFmqw@mail.gmail.com

diff --git a/src/pl/tcl/pltcl.c b/src/pl/tcl/pltcl.c
index d6b72f7d6862395a420f3455355c28ef7d407f10..48a3206da1ce8e51009889e37f153a5db110d7b6 100644 (file)
--- a/src/pl/tcl/pltcl.c
+++ b/src/pl/tcl/pltcl.c
@@ -2104,6 +2104,7 @@ static int
 pltcl_SPI_prepare(ClientData cdata, Tcl_Interp *interp,
                                  int argc, CONST84 char *argv[])
 {
+       volatile MemoryContext plan_cxt = NULL;
        int                     nargs;
        CONST84 char **args;
        pltcl_query_desc *qdesc;
@@ -2132,13 +2133,24 @@ pltcl_SPI_prepare(ClientData cdata, Tcl_Interp *interp,
 
        /************************************************************
         * Allocate the new querydesc structure
+        *
+        * struct qdesc and subsidiary data all live in plan_cxt.  Note that if the
+        * function is recompiled for whatever reason, permanent memory leaks
+        * occur.  FIXME someday.
         ************************************************************/
-       qdesc = (pltcl_query_desc *) malloc(sizeof(pltcl_query_desc));
+       plan_cxt = AllocSetContextCreate(TopMemoryContext,
+                                                                        "PL/TCL spi_prepare query",
+                                                                        ALLOCSET_SMALL_MINSIZE,
+                                                                        ALLOCSET_SMALL_INITSIZE,
+                                                                        ALLOCSET_SMALL_MAXSIZE);
+       MemoryContextSwitchTo(plan_cxt);
+       qdesc = (pltcl_query_desc *) palloc0(sizeof(pltcl_query_desc));
        snprintf(qdesc->qname, sizeof(qdesc->qname), "%p", qdesc);
        qdesc->nargs = nargs;
-       qdesc->argtypes = (Oid *) malloc(nargs * sizeof(Oid));
-       qdesc->arginfuncs = (FmgrInfo *) malloc(nargs * sizeof(FmgrInfo));
-       qdesc->argtypioparams = (Oid *) malloc(nargs * sizeof(Oid));
+       qdesc->argtypes = (Oid *) palloc(nargs * sizeof(Oid));
+       qdesc->arginfuncs = (FmgrInfo *) palloc(nargs * sizeof(FmgrInfo));
+       qdesc->argtypioparams = (Oid *) palloc(nargs * sizeof(Oid));
+       MemoryContextSwitchTo(oldcontext);
 
        /************************************************************
         * Execute the prepare inside a sub-transaction, so we can cope with
@@ -2166,7 +2178,7 @@ pltcl_SPI_prepare(ClientData cdata, Tcl_Interp *interp,
                        getTypeInputInfo(typId, &typInput, &typIOParam);
 
                        qdesc->argtypes[i] = typId;
-                       perm_fmgr_info(typInput, &(qdesc->arginfuncs[i]));
+                       fmgr_info_cxt(typInput, &(qdesc->arginfuncs[i]), plan_cxt);
                        qdesc->argtypioparams[i] = typIOParam;
                }
 
@@ -2193,10 +2205,7 @@ pltcl_SPI_prepare(ClientData cdata, Tcl_Interp *interp,
        {
                pltcl_subtrans_abort(interp, oldcontext, oldowner);
 
-               free(qdesc->argtypes);
-               free(qdesc->arginfuncs);
-               free(qdesc->argtypioparams);
-               free(qdesc);
+               MemoryContextDelete(plan_cxt);
                ckfree((char *) args);
 
                return TCL_ERROR;