libhtml: fix potential linked list corruption

the difficulty is freeing items while parsing because items might already
be linked into various linked lists like in docinfo.images or form.fiels.
so we link images, tables and formfields to the docinfo as the final step
of getitems() pass using the new recursive function linkitems(). as only
reachable items get linked theres no danger of dangeling pointers.

1 files changed, 69 insertions, 38 deletions

diff --git a/sys/src/libhtml/build.c b/sys/src/libhtml/build.c
index 50e5b1624..7b99d64a1 100644
--- a/sys/src/libhtml/build.c
+++ b/sys/src/libhtml/build.c
@@ -54,6 +54,7 @@ struct ItemSource
 	int			ntables;
 	int			nanchors;
 	int			nframes;
+	Formfield*	curfield;
 	Form*		curform;
 	Map*		curmap;
 	Table*		tabstk;
@@ -358,6 +359,7 @@ newitemsource(Docinfo* di)
 	is->ntables = 0;
 	is->nanchors = 0;
 	is->nframes = 0;
+	is->curfield = nil;
 	is->curform = nil;
 	is->curmap = nil;
 	is->tabstk = nil;
@@ -365,6 +367,62 @@ newitemsource(Docinfo* di)
 	return is;
 }
 
+static void
+linkitems(Docinfo *di, Item *it)
+{
+	Formfield *ff;
+	Tablecell *c;
+	Table *tt;
+
+	while(it != nil){
+		switch(it->tag) {
+		case Iimagetag:
+			/* link image to docinfo */
+			((Iimage*)it)->nextimage = di->images;
+			di->images = (Iimage*)it;
+			break;
+		case Iformfieldtag:
+			/* link formfield to form */
+			ff = ((Iformfield*)it)->formfield;
+			if(ff != nil && ff->form != nil){
+				for(ff = ff->form->fields; ff != nil; ff = ff->next){
+					if(ff == ((Iformfield*)it)->formfield)
+						goto Next;
+					if(ff->next == nil)
+						break;
+				}
+				((Iformfield*)it)->formfield->next = nil;
+				if(ff != nil){
+					ff->next = ((Iformfield*)it)->formfield;
+					ff = ff->next;
+				} else {
+					ff = ((Iformfield*)it)->formfield;
+					ff->form->fields = ff;
+				}
+				linkitems(di, ff->image);
+			}
+			break;
+		case Itabletag:
+			/* link table to docinfo */
+			tt = ((Itable*)it)->table;
+			if(tt == nil)
+				break;
+			tt->tabletok = nil;
+			tt->next = di->tables;
+			di->tables = tt;
+			linkitems(di, tt->caption);
+			for(c = tt->cells; c != nil; c = c->next)
+				linkitems(di, c->content);
+			break;
+		case Ifloattag:
+			linkitems(di, ((Ifloat*)it)->item);
+			break;
+		}
+	Next:
+		it = it->next;
+	}
+}
+
 static Item *getitems(ItemSource* is, uchar* data, int datalen);
 
 // Parse an html document and create a list of layout items.
@@ -453,7 +511,6 @@ getitems(ItemSource* is, uchar* data, int datalen)
 	Rune*	script;
 	Map*	map;
 	Form*	frm;
-	Iimage*	ii;
 	Kidinfo*	kd;
 	Kidinfo*	ks;
 	Kidinfo*	pks;
@@ -693,19 +750,9 @@ getitems(ItemSource* is, uchar* data, int datalen)
 				bg = makebackground(nil, acolorval(tok, Abgcolor, di->background.color));
 				bgurl = aurlval(tok, Abackground, nil, di->base);
 				if(bgurl != nil) {
-					if(di->backgrounditem != nil){
-						Iimage **ii;
-						for(ii=&di->images; *ii != nil; ii = &((*ii)->nextimage)){
-							if(*ii == di->backgrounditem){
-								*ii = di->backgrounditem->nextimage;
-								break;
-							}
-						}
+					if(di->backgrounditem != nil)
 						freeitem(di->backgrounditem);
-					}
 					di->backgrounditem = (Iimage*)newiimage(bgurl, nil, ALnone, 0, 0, 0, 0, 0, 0, nil);
-					di->backgrounditem->nextimage = di->images;
-					di->images = di->backgrounditem;
 				}
 				ps->curbg = bg;
 				di->background = bg;
@@ -902,8 +949,6 @@ getitems(ItemSource* is, uchar* data, int datalen)
 						fprint(2, "warning: unexpected </FORM>\n");
 					continue;
 				}
-				// put fields back in input order
-				is->curform->fields = (Formfield*)_revlist((List*)is->curform->fields);
 				is->curform = nil;
 				break;
 
@@ -1092,10 +1137,6 @@ getitems(ItemSource* is, uchar* data, int datalen)
 					ps->skipwhite = 0;
 					additem(ps, img, tok);
 				}
-				if(!ps->skipping) {
-					((Iimage*)img)->nextimage = di->images;
-					di->images = (Iimage*)img;
-				}
 				ps->curanchor = oldcuranchor;
 				break;
 
@@ -1107,7 +1148,7 @@ getitems(ItemSource* is, uchar* data, int datalen)
 						fprint(2, "<INPUT> not inside <FORM>\n");
 					continue;
 				}
-				is->curform->fields = field = newformfield(
+				field = newformfield(
 						atabval(tok, Atype, input_tab, NINPUTTAB, Ftext),
 						++is->curform->nfields,
 						is->curform,
@@ -1115,7 +1156,7 @@ getitems(ItemSource* is, uchar* data, int datalen)
 						aval(tok, Avalue),
 						auintval(tok, Asize, 0),
 						auintval(tok, Amaxlength, 1000),
-						is->curform->fields);
+						nil);
 				if(aflagval(tok, Achecked))
 					field->flags = FFchecked;
 
@@ -1167,9 +1208,6 @@ getitems(ItemSource* is, uchar* data, int datalen)
 						atabval(tok, Aalign, align_tab, NALIGNTAB, ALbottom),
 						auintval(tok, Awidth, 0), auintval(tok, Aheight, 0),
 						0, 0, 0, 0, nil);
-					ii = (Iimage*)field->image;
-					ii->nextimage = di->images;
-					di->images = ii;
 					break;
 
 				case Freset:
@@ -1202,15 +1240,13 @@ getitems(ItemSource* is, uchar* data, int datalen)
 						di->forms);
 				di->forms = frm;
 				ff = newformfield(Ftext,
-						1,
+						++frm->nfields,
 						frm,
 						_Strdup(L"_ISINDEX_"),
 						nil,
 						50,
 						1000,
 						nil);
-				frm->fields = ff;
-				frm->nfields = 1;
 				additem(ps, newiformfield(ff), tok);
 				addbrk(ps, 1, 0);
 				break;
@@ -1407,15 +1443,14 @@ getitems(ItemSource* is, uchar* data, int datalen)
 						fprint(2, "<SELECT> not inside <FORM>\n");
 					continue;
 				}
-				field = newformfield(Fselect,
+				is->curfield = field = newformfield(Fselect,
 					++is->curform->nfields,
 					is->curform,
 					aval(tok, Aname),
 					nil,
 					auintval(tok, Asize, 0),
 					0,
-					is->curform->fields);
-				is->curform->fields = field;
+					nil);
 				if(aflagval(tok, Amultiple))
 					field->flags = FFmultiple;
 				ffit = newiformfield(field);
@@ -1429,16 +1464,17 @@ getitems(ItemSource* is, uchar* data, int datalen)
 				break;
 
 			case Tselect+RBRA:
-				if(is->curform == nil || is->curform->fields == nil) {
+				if(is->curform == nil || is->curfield == nil) {
 					if(warn)
 						fprint(2, "warning: unexpected </SELECT>\n");
 					continue;
 				}
-				field = is->curform->fields;
+				field = is->curfield;
 				if(field->ftype != Fselect)
 					continue;
 				// put options back in input order
 				field->options = (Option*)_revlist((List*)field->options);
+				is->curfield = nil;
 				break;
 
 			// <!ELEMENT (STRIKE|U) - - (%text)*>
@@ -1553,8 +1589,6 @@ getitems(ItemSource* is, uchar* data, int datalen)
 				}
 				else
 					is->tabstk = is->tabstk->next;
-				curtab->next = di->tables;
-				di->tables = curtab;
 				curtab = is->tabstk;
 				if(!isempty)
 					addbrk(ps, 0, 0);
@@ -1649,8 +1683,7 @@ getitems(ItemSource* is, uchar* data, int datalen)
 					nil,
 					0,
 					0,
-					is->curform->fields);
-				is->curform->fields = field;
+					nil);
 				field->rows = auintval(tok, Arows, 3);
 				field->cols = auintval(tok, Acols, 50);
 				field->value = getpcdata(toks, tokslen, &toki);
@@ -1803,8 +1836,6 @@ getitems(ItemSource* is, uchar* data, int datalen)
 		}
 		if(is->tabstk != nil)
 			is->tabstk = is->tabstk->next;
-		curtab->next = di->tables;
-		di->tables = curtab;
 		curtab = is->tabstk;
 	}
 	outerps = lastps(ps);
@@ -1828,6 +1859,7 @@ return_ans:
 		else
 			printitems(ans, "getitems returning:");
 	}
+	linkitems(di, ans);
 	_freetokens(toks, tokslen);
 	return ans;
 }
@@ -3738,7 +3770,6 @@ newtable(int tableid, Align align, Dimen width, int border,
 	t->caption_place = ALbottom;
 	t->caption_lay = nil;
 	t->tabletok = tok;
-	t->tabletok = nil;
 	t->next = link;
 	return t;
 }