resolv: Move ns_name_unpack to its own file and into libc

Reformat to GNU style. Avoid out-of-bounds buffer arithmetic.
Eliminate the labellen function.

The symbol was moved using scripts/move-symbol-to-libc.py.

Reviewed-by: Carlos O'Donell <carlos@redhat.com>
Tested-by: Carlos O'Donell <carlos@redhat.com>

resolv/ns_name_unpack.c

@@ -0,0 +1,115 @@
+/* De-compressing DNS domain names into binary-encoded uncompressed name.
+ * Copyright (c) 2004 by Internet Systems Consortium, Inc. ("ISC")
+ * Copyright (c) 1996,1999 by Internet Software Consortium.
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND ISC DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS.  IN NO EVENT SHALL ISC BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT
+ * OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#include <arpa/nameser.h>
+#include <errno.h>
+#include <shlib-compat.h>
+#include <stddef.h>
+#include <string.h>
+
+/* Unpack a domain name from a message, source may be compressed.
+   Returns -1 if it fails, or consumed octets if it succeeds.  */
+int
+___ns_name_unpack (const unsigned char *msg, const unsigned char *eom,
+                   const unsigned char *src, unsigned char *dst, size_t dstsiz)
+{
+  const unsigned char *srcp, *dstlim;
+  unsigned char *dstp;
+  int n, len, checked;
+
+  len = -1;
+  checked = 0;
+  dstp = dst;
+  srcp = src;
+  dstlim = dst + dstsiz;
+  if (srcp < msg || srcp >= eom)
+    {
+      __set_errno (EMSGSIZE);
+      return -1;
+    }
+  /* Fetch next label in domain name.  */
+  while ((n = *srcp++) != 0)
+    {
+      /* Check for indirection.  */
+      switch (n & NS_CMPRSFLGS)
+        {
+        case 0:
+          /* Limit checks.  */
+          if (n >= 64)
+            {
+              __set_errno (EMSGSIZE);
+              return -1;
+            }
+          /* NB: n + 1 and >= to cover the *dstp = '\0' assignment
+             below.  */
+          if (n + 1 >= dstlim - dstp || n >= eom - srcp)
+            {
+              __set_errno (EMSGSIZE);
+              return -1;
+            }
+          checked += n + 1;
+          *dstp++ = n;
+          memcpy (dstp, srcp, n);
+          dstp += n;
+          srcp += n;
+          break;
+
+        case NS_CMPRSFLGS:
+          if (srcp >= eom)
+            {
+              __set_errno (EMSGSIZE);
+              return -1;
+            }
+          if (len < 0)
+            len = srcp - src + 1;
+          {
+            int target = ((n & 0x3f) << 8) | *srcp;
+            if (target >= eom - msg)
+              {
+              /* Out of range.  */
+                __set_errno (EMSGSIZE);
+                return -1;
+            }
+            srcp = msg + target;
+          }
+          checked += 2;
+          /* Check for loops in the compressed name; if we've looked
+             at the whole message, there must be a loop.  */
+          if (checked >= eom - msg)
+            {
+              __set_errno (EMSGSIZE);
+              return -1;
+            }
+          break;
+
+        default:
+          __set_errno (EMSGSIZE);
+          return -1;
+        }
+    }
+  *dstp = '\0';
+  if (len < 0)
+    len = srcp - src;
+  return len;
+}
+versioned_symbol (libc, ___ns_name_unpack, ns_name_unpack, GLIBC_2_34);
+versioned_symbol (libc, ___ns_name_unpack, __ns_name_unpack, GLIBC_PRIVATE);
+libc_hidden_ver (___ns_name_unpack, __ns_name_unpack)
+
+#if OTHER_SHLIB_COMPAT (libresolv, GLIBC_2_9, GLIBC_2_34)
+compat_symbol (libresolv, ___ns_name_unpack, ns_name_unpack, GLIBC_2_9);
+#endif