0032-nss_dns-Rewrite-getanswer_r-to-match-getanswer_ptr-b.patch

From 78c8ef21fa54e994451d5b42ead6080d99a88a49 Mon Sep 17 00:00:00 2001
From: Florian Weimer <fweimer@redhat.com>
Date: Tue, 30 Aug 2022 10:02:49 +0200
Subject: [PATCH 32/39] nss_dns: Rewrite getanswer_r to match getanswer_ptr
 (bug 12154, bug 29305)

Allocate the pointer arrays only at the end, when their sizes
are known.  This addresses bug 29305.

Skip over invalid names instead of failing lookups.  This partially
fixes bug 12154 (for gethostbyname, fixing getaddrinfo requires
different changes).

Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org>
(cherry picked from commit d101d836e7e4bd1d4e4972b0e0bd0a55c9b650fa)
---
 resolv/nss_dns/dns-host.c | 478 ++++++++++++++------------------------
 1 file changed, 180 insertions(+), 298 deletions(-)

diff --git a/resolv/nss_dns/dns-host.c b/resolv/nss_dns/dns-host.c
index 8e38583e15..b887e77e9c 100644
--- a/resolv/nss_dns/dns-host.c
+++ b/resolv/nss_dns/dns-host.c
@@ -107,12 +107,19 @@ typedef union querybuf
   u_char buf[MAXPACKET];
 } querybuf;
 
-static enum nss_status getanswer_r (struct resolv_context *ctx,
-				    const querybuf *answer, int anslen,
-				    const char *qname, int qtype,
-				    struct hostent *result, char *buffer,
-				    size_t buflen, int *errnop, int *h_errnop,
-				    int32_t *ttlp, char **canonp);
+/* For historic reasons, pointers to IP addresses are char *, so use a
+   single list type for addresses and host names.  */
+#define DYNARRAY_STRUCT ptrlist
+#define DYNARRAY_ELEMENT char *
+#define DYNARRAY_PREFIX ptrlist_
+#include <malloc/dynarray-skeleton.c>
+
+static enum nss_status getanswer_r (unsigned char *packet, size_t packetlen,
+				    uint16_t qtype, struct alloc_buffer *abuf,
+				    struct ptrlist *addresses,
+				    struct ptrlist *aliases,
+				    int *errnop, int *h_errnop, int32_t *ttlp);
+static void addrsort (struct resolv_context *ctx, char **ap, int num);
 static enum nss_status getanswer_ptr (unsigned char *packet, size_t packetlen,
 				      struct alloc_buffer *abuf,
 				      char **hnamep, int *errnop,
@@ -184,12 +191,6 @@ gethostbyname3_context (struct resolv_context *ctx,
 			char *buffer, size_t buflen, int *errnop,
 			int *h_errnop, int32_t *ttlp, char **canonp)
 {
-  union
-  {
-    querybuf *buf;
-    u_char *ptr;
-  } host_buffer;
-  querybuf *orig_host_buffer;
   char tmp[NS_MAXDNAME];
   int size, type, n;
   const char *cp;
@@ -223,10 +224,12 @@ gethostbyname3_context (struct resolv_context *ctx,
       && (cp = __res_context_hostalias (ctx, name, tmp, sizeof (tmp))) != NULL)
     name = cp;
 
-  host_buffer.buf = orig_host_buffer = (querybuf *) alloca (1024);
+  unsigned char dns_packet_buffer[1024];
+  unsigned char *alt_dns_packet_buffer = dns_packet_buffer;
 
-  n = __res_context_search (ctx, name, C_IN, type, host_buffer.buf->buf,
-			    1024, &host_buffer.ptr, NULL, NULL, NULL, NULL);
+  n = __res_context_search (ctx, name, C_IN, type,
+			    dns_packet_buffer, sizeof (dns_packet_buffer),
+			    &alt_dns_packet_buffer, NULL, NULL, NULL, NULL);
   if (n < 0)
     {
       switch (errno)
@@ -255,12 +258,77 @@ gethostbyname3_context (struct resolv_context *ctx,
 	__set_errno (olderr);
     }
   else
-    status = getanswer_r
-      (ctx, host_buffer.buf, n, name, type, result, buffer, buflen,
-       errnop, h_errnop, ttlp, canonp);
+    {
+      struct alloc_buffer abuf = alloc_buffer_create (buffer, buflen);
 
-  if (host_buffer.buf != orig_host_buffer)
-    free (host_buffer.buf);
+      struct ptrlist addresses;
+      ptrlist_init (&addresses);
+      struct ptrlist aliases;
+      ptrlist_init (&aliases);
+
+      status = getanswer_r (alt_dns_packet_buffer, n, type,
+			    &abuf, &addresses, &aliases,
+			    errnop, h_errnop, ttlp);
+      if (status == NSS_STATUS_SUCCESS)
+	{
+	  if (ptrlist_has_failed (&addresses)
+	      || ptrlist_has_failed (&aliases))
+	    {
+	      /* malloc failure.  Do not retry using the ERANGE protocol.  */
+	      *errnop = ENOMEM;
+	      *h_errnop = NETDB_INTERNAL;
+	      status = NSS_STATUS_UNAVAIL;
+	    }
+
+	  /* Reserve the address and alias arrays in the result
+	     buffer.  Both are NULL-terminated, but the first element
+	     of the alias array is stored in h_name, so no extra space
+	     for the NULL terminator is needed there.  */
+	  result->h_addr_list
+	    = alloc_buffer_alloc_array (&abuf, char *,
+					ptrlist_size (&addresses) + 1);
+	  result->h_aliases
+	    = alloc_buffer_alloc_array (&abuf, char *,
+					ptrlist_size (&aliases));
+	  if (alloc_buffer_has_failed (&abuf))
+	    {
+	      /* Retry using the ERANGE protocol.  */
+	      *errnop = ERANGE;
+	      *h_errnop = NETDB_INTERNAL;
+	      status = NSS_STATUS_TRYAGAIN;
+	    }
+	  else
+	    {
+	      /* Copy the address list and NULL-terminate it.  */
+	      memcpy (result->h_addr_list, ptrlist_begin (&addresses),
+		      ptrlist_size (&addresses) * sizeof (char *));
+	      result->h_addr_list[ptrlist_size (&addresses)] = NULL;
+
+	      /* Sort the address list if requested.  */
+	      if (type == T_A && __resolv_context_sort_count (ctx) > 0)
+		addrsort (ctx, result->h_addr_list, ptrlist_size (&addresses));
+
+	      /* Copy the aliases,  excluding the last one. */
+	      memcpy (result->h_aliases, ptrlist_begin (&aliases),
+		      (ptrlist_size (&aliases) - 1) * sizeof (char *));
+	      result->h_aliases[ptrlist_size (&aliases) - 1] = NULL;
+
+	      /* The last alias goes into h_name.  */
+	      assert (ptrlist_size (&aliases) >= 1);
+	      result->h_name = ptrlist_end (&aliases)[-1];
+
+	      /* This is also the canonical name.  */
+	      if (canonp != NULL)
+		*canonp = result->h_name;
+	    }
+	}
+
+      ptrlist_free (&aliases);
+      ptrlist_free (&addresses);
+    }
+
+  if (alt_dns_packet_buffer != dns_packet_buffer)
+    free (alt_dns_packet_buffer);
   return status;
 }
 
@@ -614,314 +682,128 @@ addrsort (struct resolv_context *ctx, char **ap, int num)
 	break;
 }
 
-static enum nss_status
-getanswer_r (struct resolv_context *ctx,
-	     const querybuf *answer, int anslen, const char *qname, int qtype,
-	     struct hostent *result, char *buffer, size_t buflen,
-	     int *errnop, int *h_errnop, int32_t *ttlp, char **canonp)
+/* Convert the uncompressed, binary domain name CDNAME into its
+   textual representation and add it to the end of ALIASES, allocating
+   space for a copy of the name from ABUF.  Skip adding the name if it
+   is not a valid host name, and return false in that case, otherwise
+   true.  */
+static bool
+getanswer_r_store_alias (const unsigned char *cdname,
+			 struct alloc_buffer *abuf,
+			 struct ptrlist *aliases)
 {
-  struct host_data
-  {
-    char *aliases[MAX_NR_ALIASES];
-    unsigned char host_addr[16];	/* IPv4 or IPv6 */
-    char *h_addr_ptrs[0];
-  } *host_data;
-  int linebuflen;
-  const HEADER *hp;
-  const u_char *end_of_message, *cp;
-  int n, ancount, qdcount;
-  int haveanswer, had_error;
-  char *bp, **ap, **hap;
-  char tbuf[MAXDNAME];
-  u_char packtmp[NS_MAXCDNAME];
-  uintptr_t pad = -(uintptr_t) buffer % __alignof__ (struct host_data);
-  buffer += pad;
-  buflen = buflen > pad ? buflen - pad : 0;
-  if (__glibc_unlikely (buflen < sizeof (struct host_data)))
-    {
-      /* The buffer is too small.  */
-    too_small:
-      *errnop = ERANGE;
-      *h_errnop = NETDB_INTERNAL;
-      return NSS_STATUS_TRYAGAIN;
-    }
-  host_data = (struct host_data *) buffer;
-  linebuflen = buflen - sizeof (struct host_data);
-  if (buflen - sizeof (struct host_data) != linebuflen)
-    linebuflen = INT_MAX;
-
-  result->h_name = NULL;
-  end_of_message = answer->buf + anslen;
-
-  /*
-   * find first satisfactory answer
-   */
-  hp = &answer->hdr;
-  ancount = ntohs (hp->ancount);
-  qdcount = ntohs (hp->qdcount);
-  cp = answer->buf + HFIXEDSZ;
-  if (__glibc_unlikely (qdcount != 1))
-    {
-      *h_errnop = NO_RECOVERY;
-      return NSS_STATUS_UNAVAIL;
-    }
-  if (sizeof (struct host_data) + (ancount + 1) * sizeof (char *) >= buflen)
-    goto too_small;
-  bp = (char *) &host_data->h_addr_ptrs[ancount + 1];
-  linebuflen -= (ancount + 1) * sizeof (char *);
-
-  n = __ns_name_unpack (answer->buf, end_of_message, cp,
-			packtmp, sizeof packtmp);
-  if (n != -1 && __ns_name_ntop (packtmp, bp, linebuflen) == -1)
-    {
-      if (__glibc_unlikely (errno == EMSGSIZE))
-	goto too_small;
-
-      n = -1;
-    }
+  /* Filter out domain names that are not host names.  */
+  if (!__res_binary_hnok (cdname))
+    return false;
+
+  /* Note: Not NS_MAXCDNAME, so that __ns_name_ntop implicitly checks
+     for length.  */
+  char dname[MAXHOSTNAMELEN + 1];
+  if (__ns_name_ntop (cdname, dname, sizeof (dname)) < 0)
+    return false;
+  /* Do not report an error on allocation failure, instead store NULL
+     or do nothing.  getanswer_r's caller will see NSS_STATUS_SUCCESS
+     and detect the memory allocation failure or buffer space
+     exhaustion, and report it accordingly.  */
+  ptrlist_add (aliases, alloc_buffer_copy_string (abuf, dname));
+  return true;
+}
 
-  if (__glibc_unlikely (n < 0))
-    {
-      *errnop = errno;
-      *h_errnop = NO_RECOVERY;
-      return NSS_STATUS_UNAVAIL;
-    }
-  if (__glibc_unlikely (__libc_res_hnok (bp) == 0))
+static enum nss_status __attribute__ ((noinline))
+getanswer_r (unsigned char *packet, size_t packetlen, uint16_t qtype,
+	     struct alloc_buffer *abuf,
+	     struct ptrlist *addresses, struct ptrlist *aliases,
+	     int *errnop, int *h_errnop, int32_t *ttlp)
+{
+  struct ns_rr_cursor c;
+  if (!__ns_rr_cursor_init (&c, packet, packetlen))
     {
-      errno = EBADMSG;
-      *errnop = EBADMSG;
+      /* This should not happen because __res_context_query already
+	 perfroms response validation.  */
       *h_errnop = NO_RECOVERY;
       return NSS_STATUS_UNAVAIL;
     }
-  cp += n + QFIXEDSZ;
 
-  if (qtype == T_A || qtype == T_AAAA)
+  /* Treat the QNAME just like an alias.  Error out if it is not a
+     valid host name.  */
+  if (ns_rr_cursor_rcode (&c) == NXDOMAIN
+      || !getanswer_r_store_alias (ns_rr_cursor_qname (&c), abuf, aliases))
     {
-      /* res_send() has already verified that the query name is the
-       * same as the one we sent; this just gets the expanded name
-       * (i.e., with the succeeding search-domain tacked on).
-       */
-      n = strlen (bp) + 1;             /* for the \0 */
-      if (n >= MAXHOSTNAMELEN)
-	{
-	  *h_errnop = NO_RECOVERY;
-	  *errnop = ENOENT;
-	  return NSS_STATUS_TRYAGAIN;
-	}
-      result->h_name = bp;
-      bp += n;
-      linebuflen -= n;
-      if (linebuflen < 0)
-	goto too_small;
-      /* The qname can be abbreviated, but h_name is now absolute. */
-      qname = result->h_name;
+      if (ttlp != NULL)
+	/* No negative caching.  */
+	*ttlp = 0;
+      *h_errnop = HOST_NOT_FOUND;
+      *errnop = ENOENT;
+      return NSS_STATUS_NOTFOUND;
     }
 
-  ap = host_data->aliases;
-  *ap = NULL;
-  result->h_aliases = host_data->aliases;
-  hap = host_data->h_addr_ptrs;
-  *hap = NULL;
-  result->h_addr_list = host_data->h_addr_ptrs;
-  haveanswer = 0;
-  had_error = 0;
+  int ancount = ns_rr_cursor_ancount (&c);
+  const unsigned char *expected_name = ns_rr_cursor_qname (&c);
+  /* expected_name may be updated to point into this buffer.  */
+  unsigned char name_buffer[NS_MAXCDNAME];
 
-  while (ancount-- > 0 && cp < end_of_message && had_error == 0)
+  for (; ancount > 0; --ancount)
     {
-      int type, class;
-
-      n = __ns_name_unpack (answer->buf, end_of_message, cp,
-			    packtmp, sizeof packtmp);
-      if (n != -1 && __ns_name_ntop (packtmp, bp, linebuflen) == -1)
-	{
-	  if (__glibc_unlikely (errno == EMSGSIZE))
-	    goto too_small;
-
-	  n = -1;
-	}
-
-      if (__glibc_unlikely (n < 0 || __libc_res_hnok (bp) == 0))
-	{
-	  ++had_error;
-	  continue;
-	}
-      cp += n;				/* name */
-
-      if (__glibc_unlikely (cp + 10 > end_of_message))
+      struct ns_rr_wire rr;
+      if (!__ns_rr_cursor_next (&c, &rr))
 	{
-	  ++had_error;
-	  continue;
+	  *h_errnop = NO_RECOVERY;
+	  return NSS_STATUS_UNAVAIL;
 	}
 
-      NS_GET16 (type, cp);
-      NS_GET16 (class, cp);
-      int32_t ttl;
-      NS_GET32 (ttl, cp);
-      NS_GET16 (n, cp);		/* RDATA length.  */
-
-      if (end_of_message - cp < n)
-	{
-	  /* RDATA extends beyond the end of the packet.  */
-	  ++had_error;
-	  continue;
-	}
+      /* Skip over records with the wrong class.  */
+      if (rr.rclass != C_IN)
+	continue;
 
-      if (__glibc_unlikely (class != C_IN))
-	{
-	  /* XXX - debug? syslog? */
-	  cp += n;
-	  continue;			/* XXX - had_error++ ? */
-	}
+      /* Update TTL for recognized record types.  */
+      if ((rr.rtype == T_CNAME || rr.rtype == qtype)
+	  && ttlp != NULL && *ttlp > rr.ttl)
+	*ttlp = rr.ttl;
 
-      if (type == T_CNAME)
+      if (rr.rtype == T_CNAME)
 	{
-	  /* A CNAME could also have a TTL entry.  */
-	  if (ttlp != NULL && ttl < *ttlp)
-	      *ttlp = ttl;
-
-	  if (ap >= &host_data->aliases[MAX_NR_ALIASES - 1])
-	    continue;
-	  n = __libc_dn_expand (answer->buf, end_of_message, cp,
-				tbuf, sizeof tbuf);
-	  if (__glibc_unlikely (n < 0 || __libc_res_hnok (tbuf) == 0))
-	    {
-	      ++had_error;
-	      continue;
-	    }
-	  cp += n;
-	  /* Store alias.  */
-	  *ap++ = bp;
-	  n = strlen (bp) + 1;		/* For the \0.  */
-	  if (__glibc_unlikely (n >= MAXHOSTNAMELEN))
-	    {
-	      ++had_error;
-	      continue;
-	    }
-	  bp += n;
-	  linebuflen -= n;
-	  /* Get canonical name.  */
-	  n = strlen (tbuf) + 1;	/* For the \0.  */
-	  if (__glibc_unlikely (n > linebuflen))
-	    goto too_small;
-	  if (__glibc_unlikely (n >= MAXHOSTNAMELEN))
+	  /* NB: No check for owner name match, based on historic
+	     precedent.  Record the CNAME target as the new expected
+	     name.  */
+	  int n = __ns_name_unpack (c.begin, c.end, rr.rdata,
+				    name_buffer, sizeof (name_buffer));
+	  if (n < 0)
 	    {
-	      ++had_error;
-	      continue;
+	      *h_errnop = NO_RECOVERY;
+	      return NSS_STATUS_UNAVAIL;
 	    }
-	  result->h_name = bp;
-	  bp = __mempcpy (bp, tbuf, n);	/* Cannot overflow.  */
-	  linebuflen -= n;
-	  continue;
+	  /* And store the new name as an alias.  */
+	  getanswer_r_store_alias (name_buffer, abuf, aliases);
+	  expected_name = name_buffer;
 	}
-
-      if (__glibc_unlikely (type != qtype))
+      else if (rr.rtype == qtype
+	       && __ns_samebinaryname (rr.rname, expected_name)
+	       && rr.rdlength == rrtype_to_rdata_length (qtype))
 	{
-	  cp += n;
-	  continue;			/* XXX - had_error++ ? */
+	  /* Make a copy of the address and store it.  Increase the
+	     alignment to 4, in case there are applications out there
+	     that expect at least this level of address alignment.  */
+	  ptrlist_add (addresses, (char *) alloc_buffer_next (abuf, uint32_t));
+	  alloc_buffer_copy_bytes (abuf, rr.rdata, rr.rdlength);
 	}
-
-      switch (type)
-	{
-	case T_A:
-	case T_AAAA:
-	  if (__glibc_unlikely (__strcasecmp (result->h_name, bp) != 0))
-	    {
-	      cp += n;
-	      continue;			/* XXX - had_error++ ? */
-	    }
-
-	  /* Stop parsing at a record whose length is incorrect.  */
-	  if (n != rrtype_to_rdata_length (type))
-	    {
-	      ++had_error;
-	      break;
-	    }
-
-	  /* Skip records of the wrong type.  */
-	  if (n != result->h_length)
-	    {
-	      cp += n;
-	      continue;
-	    }
-	  if (!haveanswer)
-	    {
-	      int nn;
-
-	      /* We compose a single hostent out of the entire chain of
-	         entries, so the TTL of the hostent is essentially the lowest
-		 TTL in the chain.  */
-	      if (ttlp != NULL && ttl < *ttlp)
-		*ttlp = ttl;
-	      if (canonp != NULL)
-		*canonp = bp;
-	      result->h_name = bp;
-	      nn = strlen (bp) + 1;	/* for the \0 */
-	      bp += nn;
-	      linebuflen -= nn;
-	    }
-
-	  /* Provide sufficient alignment for both address
-	     families.  */
-	  enum { align = 4 };
-	  _Static_assert ((align % __alignof__ (struct in_addr)) == 0,
-			  "struct in_addr alignment");
-	  _Static_assert ((align % __alignof__ (struct in6_addr)) == 0,
-			  "struct in6_addr alignment");
-	  {
-	    char *new_bp = PTR_ALIGN_UP (bp, align);
-	    linebuflen -= new_bp - bp;
-	    bp = new_bp;
-	  }
-
-	  if (__glibc_unlikely (n > linebuflen))
-	    goto too_small;
-	  bp = __mempcpy (*hap++ = bp, cp, n);
-	  cp += n;
-	  linebuflen -= n;
-	  break;
-	default:
-	  abort ();
-	}
-      if (had_error == 0)
-	++haveanswer;
     }
 
-  if (haveanswer > 0)
+  if (ptrlist_size (addresses) == 0)
     {
-      *ap = NULL;
-      *hap = NULL;
-      /*
-       * Note: we sort even if host can take only one address
-       * in its return structures - should give it the "best"
-       * address in that case, not some random one
-       */
-      if (haveanswer > 1 && qtype == T_A
-	  && __resolv_context_sort_count (ctx) > 0)
-	addrsort (ctx, host_data->h_addr_ptrs, haveanswer);
-
-      if (result->h_name == NULL)
-	{
-	  n = strlen (qname) + 1;	/* For the \0.  */
-	  if (n > linebuflen)
-	    goto too_small;
-	  if (n >= MAXHOSTNAMELEN)
-	    goto no_recovery;
-	  result->h_name = bp;
-	  bp = __mempcpy (bp, qname, n);	/* Cannot overflow.  */
-	  linebuflen -= n;
-	}
+      /* No address record found.  */
+      if (ttlp != NULL)
+	/* No caching of negative responses.  */
+	*ttlp = 0;
 
+      *h_errnop = NO_RECOVERY;
+      *errnop = ENOENT;
+      return NSS_STATUS_TRYAGAIN;
+    }
+  else
+    {
       *h_errnop = NETDB_SUCCESS;
       return NSS_STATUS_SUCCESS;
     }
- no_recovery:
-  *h_errnop = NO_RECOVERY;
-  *errnop = ENOENT;
-  /* Special case here: if the resolver sent a result but it only
-     contains a CNAME while we are looking for a T_A or T_AAAA record,
-     we fail with NOTFOUND instead of TRYAGAIN.  */
-  return ((qtype == T_A || qtype == T_AAAA) && ap != host_data->aliases
-	   ? NSS_STATUS_NOTFOUND : NSS_STATUS_TRYAGAIN);
 }
 
 static enum nss_status
-- 
2.37.2