[Bug 2505515] nss_sss: getpwnam results in a -1 fd being passed to fstat

https://bugzilla.redhat.com/show_bug.cgi?id=2505515

--- Comment #8 from Noah Arcouette  ---
Hello, I definitely do not have the right experience to fix this but from my
efforts I've found two areas that may be the issue:

```
diff --git a/nscd/nscd_helper.c b/nscd/nscd_helper.c
index 6319fde6f2..4dfb59291b 100644
--- a/nscd/nscd_helper.c
+++ b/nscd/nscd_helper.c
@@ -315,6 +315,9 @@ __nscd_get_mapping (request_type type, const char *key,
   int *ip = (void *) CMSG_DATA (cmsg);
   mapfd = *ip;

+  if (mapfd < 0)
+    goto out_close;
+
   if (__glibc_unlikely (n != keylen && n != keylen + sizeof (mapsize)))
     goto out_close;

diff --git a/nss/makedb.c b/nss/makedb.c
index efb8f4af30..acff59a0ba 100644
--- a/nss/makedb.c
+++ b/nss/makedb.c
@@ -829,7 +829,7 @@ static int
 print_database (int fd)
 {
   struct stat64 st;
-  if (fstat64 (fd, &st) != 0)
+  if (fd < 0 || fstat64 (fd, &st) != 0)
     error (EXIT_FAILURE, errno, gettext ("cannot stat database file"));

const struct nss_db_header *header = mmap (NULL, st.st_size, PROT_READ,
```

These are both off of glibc latest, neither check fd before use. I am not
capable of testing if this patch works, though I tried. If any one in the
future thinks this error is error-ish enough then hopefully this gives them a
start and less of a headache tracking down fstat calls.

Thanks for you guy's time, 
  Noah