[glibc/release/2.28/master] nss_db: fix endent wrt NULL mappings [BZ #24695] [BZ #24696]

[DJ Delorie <dj@sourceware.org>]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=cef4c840a80372fe084effec0da1177d44b40bc0

commit cef4c840a80372fe084effec0da1177d44b40bc0
Author: DJ Delorie <dj@redhat.com>
Date:   Fri Jun 28 18:30:00 2019 -0500

    nss_db: fix endent wrt NULL mappings [BZ #24695] [BZ #24696]
    
    nss_db allows for getpwent et al to be called without a set*ent,
    but it only works once.  After the last get*ent a set*ent is
    required to restart, because the end*ent did not properly reset
    the module.  Resetting it to NULL allows for a proper restart.
    
    If the database doesn't exist, however, end*ent erroniously called
    munmap which set errno.
    
    The test case runs "makedb" inside the testroot, so needs selinux
    DSOs installed.
    
    (cherry picked from commit 99135114ba23c3110b7e4e650fabdc5e639746b7)
    (note: tests excluded as test-in-container infrastructure missing)

Diff:
---
 ChangeLog            | 8 ++++++++
 nss/nss_db/db-open.c | 6 +++++-
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/ChangeLog b/ChangeLog
index fcc0f80..d932485 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,11 @@
+2019-07-10  DJ Delorie  <dj@redhat.com>
+	    Sergei Trofimovich <slyfox@inbox.ru>
+
+	[BZ #24696]
+	[BZ #24695]
+	* nss/nss_db/db-open.c (internal_endent): Protect against NULL
+	mappings.
+
 2019-07-01  H.J. Lu  <hongjiu.lu@intel.com>
 
 	[BZ #24259]
diff --git a/nss/nss_db/db-open.c b/nss/nss_db/db-open.c
index 8538f8e..ac430f4 100644
--- a/nss/nss_db/db-open.c
+++ b/nss/nss_db/db-open.c
@@ -63,5 +63,9 @@ internal_setent (const char *file, struct nss_db_map *mapping)
 void
 internal_endent (struct nss_db_map *mapping)
 {
-  munmap (mapping->header, mapping->len);
+  if (mapping->header != NULL)
+    {
+      munmap (mapping->header, mapping->len);
+      mapping->header = NULL;
+    }
 }