nss_files: Fix /etc/aliases null pointer dereference [BZ #24059]

If /etc/aliases ends with a continuation line (a line that starts
with whitespace) which does not have a trailing newline character,
the file parser would crash due to a null pointer dereference.

Reviewed-by: Carlos O'Donell <carlos@redhat.com>

1 files changed, 10 insertions, 0 deletions

diff --git a/nss/nss_files/files-alias.c b/nss/nss_files/files-alias.c
index 540eb9c678..34d7aa84cc 100644
--- a/nss/nss_files/files-alias.c
+++ b/nss/nss_files/files-alias.c
@@ -333,6 +333,16 @@ get_next_alias (FILE *stream, const char *match, struct aliasent *result,
 		     can be ignored.  */
 		  first_unused[room_left - 1] = '\xff';
 		  line = fgets_unlocked (first_unused, room_left, stream);
+		  if (line == NULL)
+		    {
+		      /* Continuation line without any data and
+			 without a newline at the end.  Treat it as an
+			 empty line and retry, reaching EOF once
+			 more.  */
+		      line = first_unused;
+		      *line = '\0';
+		      continue;
+		    }
 		  if (first_unused[room_left - 1] != '\xff')
 		    goto no_more_room;
 		  cp = strpbrk (line, "#\n");