nscd: Fix double free in netgroupcache [BZ #27462]

In commit 745664bd798ec8fd50438605948eea594179fba1 a use-after-free
was fixed, but this led to an occasional double-free.  This patch
tracks the "live" allocation better.

Tested manually by a third party.

Related: RHBZ 1927877

Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org>
Reviewed-by: Carlos O'Donell <carlos@redhat.com>
(cherry picked from commit dca565886b5e8bd7966e15f0ca42ee5cff686673)

diff --git a/NEWS b/NEWS
index dff138e8b2e1a42162372f866716fb591032ca97..15b835bd3035928520f6898d9770ab58969bd70d 100644 (file)
--- a/NEWS
+++ b/NEWS
@@ -99,6 +99,11 @@ Security related changes:
   CVE-2020-29562: An assertion failure has been fixed in the iconv function
   when invoked with UCS4 input containing an invalid character.
 
+  CVE-2021-27645: The nameserver caching daemon (nscd), when processing
+  a request for netgroup lookup, may crash due to a double-free,
+  potentially resulting in degraded service or Denial of Service on the
+  local system.  Reported by Chris Schanzle.
+
 The following bugs are resolved with this release:
 
   [6889] 'PWD' mentioned but not specified
@@ -195,6 +200,7 @@ The following bugs are resolved with this release:
     character sets (CVE-2020-27618)
   [26383] bind_textdomain_codeset doesn't accept //TRANSLIT anymore
   [26923] Assertion failure in iconv when converting invalid UCS4 (CVE-2020-29562)
+  [27462] nscd: double-free in nscd (CVE-2021-27645)
 
 \f
 Version 2.27

diff --git a/nscd/netgroupcache.c b/nscd/netgroupcache.c
index 3adc5387d6cc87769320e8f2230ac879e20721cf..e75cbc057360c277b256a868a8fa0cc9ddc502e0 100644 (file)
--- a/nscd/netgroupcache.c
+++ b/nscd/netgroupcache.c
@@ -248,7 +248,7 @@ addgetnetgrentX (struct database_dyn *db, int fd, request_header *req,
                                             : NULL);
                                    ndomain = (ndomain ? newbuf + ndomaindiff
                                               : NULL);
-                                   buffer = newbuf;
+                                   *tofreep = buffer = newbuf;
                                  }
 
                                nhost = memcpy (buffer + bufused,
@@ -319,7 +319,7 @@ addgetnetgrentX (struct database_dyn *db, int fd, request_header *req,
                    else if (status == NSS_STATUS_TRYAGAIN && e == ERANGE)
                      {
                        buflen *= 2;
-                       buffer = xrealloc (buffer, buflen);
+                       *tofreep = buffer = xrealloc (buffer, buflen);
                      }
                    else if (status == NSS_STATUS_RETURN
                             || status == NSS_STATUS_NOTFOUND