CVE-2024-33601, CVE-2024-33602: nscd: netgroup: Use two buffers in addgetnetgrentX (bug 31680)

This avoids potential memory corruption when the underlying NSS
callback function does not use the buffer space to store all strings
(e.g., for constant strings).

Instead of custom buffer management, two scratch buffers are used.
This increases stack usage somewhat.

Scratch buffer allocation failure is handled by return -1
(an invalid timeout value) instead of terminating the process.
This fixes bug 31679.

Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org>
(cherry picked from commit c04a21e050d64a1193a6daab872bca2528bda44b)

1 files changed, 121 insertions, 98 deletions

diff --git a/nscd/netgroupcache.c b/nscd/netgroupcache.c
index fe5d10226b..72d7a52cb4 100644
--- a/nscd/netgroupcache.c
+++ b/nscd/netgroupcache.c
@@ -23,6 +23,7 @@
 #include <stdlib.h>
 #include <unistd.h>
 #include <sys/mman.h>
+#include <scratch_buffer.h>
 
 #include "../inet/netgroup.h"
 #include "nscd.h"
@@ -65,6 +66,16 @@ struct dataset
   char strdata[0];
 };
 
+/* Send a notfound response to FD.  Always returns -1 to indicate an
+   ephemeral error.  */
+static time_t
+send_notfound (int fd)
+{
+  if (fd != -1)
+    TEMP_FAILURE_RETRY (send (fd, &notfound, sizeof (notfound), MSG_NOSIGNAL));
+  return -1;
+}
+
 /* Sends a notfound message and prepares a notfound dataset to write to the
    cache.  Returns true if there was enough memory to allocate the dataset and
    returns the dataset in DATASETP, total bytes to write in TOTALP and the
@@ -83,8 +94,7 @@ do_notfound (struct database_dyn *db, int fd, request_header *req,
   total = sizeof (notfound);
   timeout = time (NULL) + db->negtimeout;
 
-  if (fd != -1)
-    TEMP_FAILURE_RETRY (send (fd, &notfound, total, MSG_NOSIGNAL));
+  send_notfound (fd);
 
   dataset = mempool_alloc (db, sizeof (struct dataset) + req->key_len, 1);
   /* If we cannot permanently store the result, so be it.  */
@@ -109,11 +119,78 @@ do_notfound (struct database_dyn *db, int fd, request_header *req,
   return cacheable;
 }
 
+struct addgetnetgrentX_scratch
+{
+  /* This is the result that the caller should use.  It can be NULL,
+     point into buffer, or it can be in the cache.  */
+  struct dataset *dataset;
+
+  struct scratch_buffer buffer;
+
+  /* Used internally in addgetnetgrentX as a staging area.  */
+  struct scratch_buffer tmp;
+
+  /* Number of bytes in buffer that are actually used.  */
+  size_t buffer_used;
+};
+
+static void
+addgetnetgrentX_scratch_init (struct addgetnetgrentX_scratch *scratch)
+{
+  scratch->dataset = NULL;
+  scratch_buffer_init (&scratch->buffer);
+  scratch_buffer_init (&scratch->tmp);
+
+  /* Reserve space for the header.  */
+  scratch->buffer_used = sizeof (struct dataset);
+  static_assert (sizeof (struct dataset) < sizeof (scratch->tmp.__space),
+		 "initial buffer space");
+  memset (scratch->tmp.data, 0, sizeof (struct dataset));
+}
+
+static void
+addgetnetgrentX_scratch_free (struct addgetnetgrentX_scratch *scratch)
+{
+  scratch_buffer_free (&scratch->buffer);
+  scratch_buffer_free (&scratch->tmp);
+}
+
+/* Copy LENGTH bytes from S into SCRATCH.  Returns NULL if SCRATCH
+   could not be resized, otherwise a pointer to the copy.  */
+static char *
+addgetnetgrentX_append_n (struct addgetnetgrentX_scratch *scratch,
+			  const char *s, size_t length)
+{
+  while (true)
+    {
+      size_t remaining = scratch->buffer.length - scratch->buffer_used;
+      if (remaining >= length)
+	break;
+      if (!scratch_buffer_grow_preserve (&scratch->buffer))
+	return NULL;
+    }
+  char *copy = scratch->buffer.data + scratch->buffer_used;
+  memcpy (copy, s, length);
+  scratch->buffer_used += length;
+  return copy;
+}
+
+/* Copy S into SCRATCH, including its null terminator.  Returns false
+   if SCRATCH could not be resized.  */
+static bool
+addgetnetgrentX_append (struct addgetnetgrentX_scratch *scratch, const char *s)
+{
+  if (s == NULL)
+    s = "";
+  return addgetnetgrentX_append_n (scratch, s, strlen (s) + 1) != NULL;
+}
+
+/* Caller must initialize and free *SCRATCH.  If the return value is
+   negative, this function has sent a notfound response.  */
 static time_t
 addgetnetgrentX (struct database_dyn *db, int fd, request_header *req,
 		 const char *key, uid_t uid, struct hashentry *he,
-		 struct datahead *dh, struct dataset **resultp,
-		 void **tofreep)
+		 struct datahead *dh, struct addgetnetgrentX_scratch *scratch)
 {
   if (__glibc_unlikely (debug_level > 0))
     {
@@ -132,14 +209,10 @@ addgetnetgrentX (struct database_dyn *db, int fd, request_header *req,
 
   char *key_copy = NULL;
   struct __netgrent data;
-  size_t buflen = MAX (1024, sizeof (*dataset) + req->key_len);
-  size_t buffilled = sizeof (*dataset);
-  char *buffer = NULL;
   size_t nentries = 0;
   size_t group_len = strlen (key) + 1;
   struct name_list *first_needed
     = alloca (sizeof (struct name_list) + group_len);
-  *tofreep = NULL;
 
   if (netgroup_database == NULL
       && !__nss_database_get (nss_database_netgroup, &netgroup_database))
@@ -151,8 +224,6 @@ addgetnetgrentX (struct database_dyn *db, int fd, request_header *req,
     }
 
   memset (&data, '\0', sizeof (data));
-  buffer = xmalloc (buflen);
-  *tofreep = buffer;
   first_needed->next = first_needed;
   memcpy (first_needed->name, key, group_len);
   data.needed_groups = first_needed;
@@ -195,8 +266,8 @@ addgetnetgrentX (struct database_dyn *db, int fd, request_header *req,
 		while (1)
 		  {
 		    int e;
-		    status = getfct.f (&data, buffer + buffilled,
-				       buflen - buffilled - req->key_len, &e);
+		    status = getfct.f (&data, scratch->tmp.data,
+				       scratch->tmp.length, &e);
 		    if (status == NSS_STATUS_SUCCESS)
 		      {
 			if (data.type == triple_val)
@@ -204,68 +275,10 @@ addgetnetgrentX (struct database_dyn *db, int fd, request_header *req,
 			    const char *nhost = data.val.triple.host;
 			    const char *nuser = data.val.triple.user;
 			    const char *ndomain = data.val.triple.domain;
-
-			    size_t hostlen = strlen (nhost ?: "") + 1;
-			    size_t userlen = strlen (nuser ?: "") + 1;
-			    size_t domainlen = strlen (ndomain ?: "") + 1;
-
-			    if (nhost == NULL || nuser == NULL || ndomain == NULL
-				|| nhost > nuser || nuser > ndomain)
-			      {
-				const char *last = nhost;
-				if (last == NULL
-				    || (nuser != NULL && nuser > last))
-				  last = nuser;
-				if (last == NULL
-				    || (ndomain != NULL && ndomain > last))
-				  last = ndomain;
-
-				size_t bufused
-				  = (last == NULL
-				     ? buffilled
-				     : last + strlen (last) + 1 - buffer);
-
-				/* We have to make temporary copies.  */
-				size_t needed = hostlen + userlen + domainlen;
-
-				if (buflen - req->key_len - bufused < needed)
-				  {
-				    buflen += MAX (buflen, 2 * needed);
-				    /* Save offset in the old buffer.  We don't
-				       bother with the NULL check here since
-				       we'll do that later anyway.  */
-				    size_t nhostdiff = nhost - buffer;
-				    size_t nuserdiff = nuser - buffer;
-				    size_t ndomaindiff = ndomain - buffer;
-
-				    char *newbuf = xrealloc (buffer, buflen);
-				    /* Fix up the triplet pointers into the new
-				       buffer.  */
-				    nhost = (nhost ? newbuf + nhostdiff
-					     : NULL);
-				    nuser = (nuser ? newbuf + nuserdiff
-					     : NULL);
-				    ndomain = (ndomain ? newbuf + ndomaindiff
-					       : NULL);
-				    *tofreep = buffer = newbuf;
-				  }
-
-				nhost = memcpy (buffer + bufused,
-						nhost ?: "", hostlen);
-				nuser = memcpy ((char *) nhost + hostlen,
-						nuser ?: "", userlen);
-				ndomain = memcpy ((char *) nuser + userlen,
-						  ndomain ?: "", domainlen);
-			      }
-
-			    char *wp = buffer + buffilled;
-			    wp = memmove (wp, nhost ?: "", hostlen);
-			    wp += hostlen;
-			    wp = memmove (wp, nuser ?: "", userlen);
-			    wp += userlen;
-			    wp = memmove (wp, ndomain ?: "", domainlen);
-			    wp += domainlen;
-			    buffilled = wp - buffer;
+			    if (!(addgetnetgrentX_append (scratch, nhost)
+				  && addgetnetgrentX_append (scratch, nuser)
+				  && addgetnetgrentX_append (scratch, ndomain)))
+			      return send_notfound (fd);
 			    ++nentries;
 			  }
 			else
@@ -317,8 +330,8 @@ addgetnetgrentX (struct database_dyn *db, int fd, request_header *req,
 		      }
 		    else if (status == NSS_STATUS_TRYAGAIN && e == ERANGE)
 		      {
-			buflen *= 2;
-			*tofreep = buffer = xrealloc (buffer, buflen);
+			if (!scratch_buffer_grow (&scratch->tmp))
+			  return send_notfound (fd);
 		      }
 		    else if (status == NSS_STATUS_RETURN
 			     || status == NSS_STATUS_NOTFOUND
@@ -351,10 +364,17 @@ addgetnetgrentX (struct database_dyn *db, int fd, request_header *req,
       goto maybe_cache_add;
     }
 
-  total = buffilled;
+  /* Capture the result size without the key appended.   */
+  total = scratch->buffer_used;
+
+  /* Make a copy of the key.  The scratch buffer must not move after
+     this point.  */
+  key_copy = addgetnetgrentX_append_n (scratch, key, req->key_len);
+  if (key_copy == NULL)
+    return send_notfound (fd);
 
   /* Fill in the dataset.  */
-  dataset = (struct dataset *) buffer;
+  dataset = scratch->buffer.data;
   timeout = datahead_init_pos (&dataset->head, total + req->key_len,
 			       total - offsetof (struct dataset, resp),
 			       he == NULL ? 0 : dh->nreloads + 1,
@@ -363,11 +383,7 @@ addgetnetgrentX (struct database_dyn *db, int fd, request_header *req,
   dataset->resp.version = NSCD_VERSION;
   dataset->resp.found = 1;
   dataset->resp.nresults = nentries;
-  dataset->resp.result_len = buffilled - sizeof (*dataset);
-
-  assert (buflen - buffilled >= req->key_len);
-  key_copy = memcpy (buffer + buffilled, key, req->key_len);
-  buffilled += req->key_len;
+  dataset->resp.result_len = total - sizeof (*dataset);
 
   /* Now we can determine whether on refill we have to create a new
      record or not.  */
@@ -398,7 +414,7 @@ addgetnetgrentX (struct database_dyn *db, int fd, request_header *req,
     if (__glibc_likely (newp != NULL))
       {
 	/* Adjust pointer into the memory block.  */
-	key_copy = (char *) newp + (key_copy - buffer);
+	key_copy = (char *) newp + (key_copy - (char *) dataset);
 
 	dataset = memcpy (newp, dataset, total + req->key_len);
 	cacheable = true;
@@ -439,7 +455,7 @@ addgetnetgrentX (struct database_dyn *db, int fd, request_header *req,
     }
 
  out:
-  *resultp = dataset;
+  scratch->dataset = dataset;
 
   return timeout;
 }
@@ -460,6 +476,9 @@ addinnetgrX (struct database_dyn *db, int fd, request_header *req,
   if (user != NULL)
     key = (char *) rawmemchr (key, '\0') + 1;
   const char *domain = *key++ ? key : NULL;
+  struct addgetnetgrentX_scratch scratch;
+
+  addgetnetgrentX_scratch_init (&scratch);
 
   if (__glibc_unlikely (debug_level > 0))
     {
@@ -475,12 +494,8 @@ addinnetgrX (struct database_dyn *db, int fd, request_header *req,
 							    group, group_len,
 							    db, uid);
   time_t timeout;
-  void *tofree;
   if (result != NULL)
-    {
-      timeout = result->head.timeout;
-      tofree = NULL;
-    }
+    timeout = result->head.timeout;
   else
     {
       request_header req_get =
@@ -489,7 +504,10 @@ addinnetgrX (struct database_dyn *db, int fd, request_header *req,
 	  .key_len = group_len
 	};
       timeout = addgetnetgrentX (db, -1, &req_get, group, uid, NULL, NULL,
-				 &result, &tofree);
+				 &scratch);
+      result = scratch.dataset;
+      if (timeout < 0)
+	goto out;
     }
 
   struct indataset
@@ -603,7 +621,7 @@ addinnetgrX (struct database_dyn *db, int fd, request_header *req,
     }
 
  out:
-  free (tofree);
+  addgetnetgrentX_scratch_free (&scratch);
   return timeout;
 }
 
@@ -613,11 +631,12 @@ addgetnetgrentX_ignore (struct database_dyn *db, int fd, request_header *req,
 			const char *key, uid_t uid, struct hashentry *he,
 			struct datahead *dh)
 {
-  struct dataset *ignore;
-  void *tofree;
-  time_t timeout = addgetnetgrentX (db, fd, req, key, uid, he, dh,
-				    &ignore, &tofree);
-  free (tofree);
+  struct addgetnetgrentX_scratch scratch;
+  addgetnetgrentX_scratch_init (&scratch);
+  time_t timeout = addgetnetgrentX (db, fd, req, key, uid, he, dh, &scratch);
+  addgetnetgrentX_scratch_free (&scratch);
+  if (timeout < 0)
+    timeout = 0;
   return timeout;
 }
 
@@ -661,5 +680,9 @@ readdinnetgr (struct database_dyn *db, struct hashentry *he,
       .key_len = he->len
     };
 
-  return addinnetgrX (db, -1, &req, db->data + he->key, he->owner, he, dh);
+  int timeout = addinnetgrX (db, -1, &req, db->data + he->key, he->owner,
+			     he, dh);
+  if (timeout < 0)
+    timeout = 0;
+  return timeout;
 }