Add sanity checks to ld.so DSBT support

This adds some DSBT index sanity checks to the runtime linker. It
catches libraries which have no index (index 0) and libraries which
try to use an already used index.

Signed-off-by: Mark Salter <msalter@redhat.com>
Signed-off-by: Bernd Schmidt <bernds@codesourcery.com>

ldso/ldso/dl-elf.c

@@ -813,13 +813,40 @@ struct elf_resolve *_dl_load_elf_shared_library(int secure,
 		int idx = tpnt->loadaddr.map->dsbt_index;
 		unsigned *dsbt = tpnt->loadaddr.map->dsbt_table;
 
+		if (idx == 0) {
+			/* This DSO has not been assigned an index */
+			_dl_dprintf(2, "%s: '%s' is missing a dsbt index assignment!\n",
+				    _dl_progname, libname);
+			_dl_exit(1);
+		}
+
 		/*
 		 * Setup dsbt slot for this module in dsbt of all modules.
 		 */
 		for (t = _dl_loaded_modules; t; t = t->next) {
 			/* find a dsbt table from another module */
-			if (ref == NULL && t != tpnt)
+			if (ref == NULL && t != tpnt) {
 				ref = t;
+
+				/* make sure index is not already used */
+				if (t->loadaddr.map->dsbt_table[idx]) {
+					struct elf_resolve *dup;
+					char *dup_name;
+
+					for (dup = _dl_loaded_modules; dup; dup = dup->next)
+						if (dup != tpnt && dup->loadaddr.map->dsbt_index == idx)
+							break;
+					if (dup)
+						dup_name = dup->libname;
+					else if (idx == 1)
+						dup_name = "runtime linker";
+					else
+						dup_name = "unknown library";
+					_dl_dprintf(2, "%s: '%s' dsbt index %d already used by %s!\n",
+						    _dl_progname, libname, idx, dup_name);
+					_dl_exit(1);
+				}
+			}
 			t->loadaddr.map->dsbt_table[idx] = (unsigned)dsbt;
 		}
 		if (ref)