[Bug nss/24696] New: endgrent() clobbers errno=ERRNO for 'group: db files' entry in /etc/nsswitch.conf

["slyfox at inbox dot ru" <sourceware-bugzilla at sourceware dot org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=24696

            Bug ID: 24696
           Summary: endgrent() clobbers errno=ERRNO for 'group: db files'
                    entry in /etc/nsswitch.conf
           Product: glibc
           Version: 2.29
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: nss
          Assignee: unassigned at sourceware dot org
          Reporter: slyfox at inbox dot ru
  Target Milestone: ---

The bug is originally reported by Guillermo D. H. at
https://bugs.gentoo.org/688246.

Here is the reproducer:

$ cat /etc/nsswitch.conf
    passwd:         files
    #group:         files
    #https://bugs.gentoo.org/688246
    group:          db files
    initgroups:     files
    shadow:         files
    gshadow:        files
    hosts:          files dns
    networks:       files dns
    protocols:      db files
    services:       db files
    ethers:         db files
    rpc:            db files
    netgroup:       db files

$ cat a.c
    #include <errno.h>
    #include <stdio.h>
    #include <string.h>
    #include <grp.h>
    int main() {
     int saved_errno;
     for (;;) {
      errno = 0;
      struct group *gr = getgrent();
      saved_errno = errno;
      if (!gr)
       break;
     }
     printf("(errno = %s)\n", strerror(saved_errno));
     printf("errno before endgrent() = %s\n", strerror(errno));
     endgrent();
     printf("errno after endgrent() = %s\n", strerror(errno));
    }

$ gcc a.c -o a
$ ./a 
    (errno = Success)
    errno before endgrent() = Success
    errno after endgrent() = Invalid argument <- the bug

The following workaround seems to be enough:

--- 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);
+  /* Avoid clobbering errno if 'header' was never allocated.  */
+  if (mapping->header != NULL)
+    {
+      munmap (mapping->header, mapping->len);
+    }
 }

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