Harden putpwent, putgrent, putspent, putspent against injection [BZ #18724]

This prevents injection of ':' and '\n' into output functions which
use the NSS files database syntax.  Critical fields (user/group names
and file system paths) are checked strictly.  For backwards
compatibility, the GECOS field is rewritten instead.

The getent program is adjusted to use the put*ent functions in libc,
instead of local copies.  This changes the behavior of getent if user
names start with '-' or '+'.

1 files changed, 13 insertions, 0 deletions

diff --git a/include/nss.h b/include/nss.h
index 0541335c18..1e8cc3910d 100644
--- a/include/nss.h
+++ b/include/nss.h
@@ -1 +1,14 @@
+#ifndef _NSS_H
 #include <nss/nss.h>
+
+#define NSS_INVALID_FIELD_CHARACTERS ":\n"
+extern const char __nss_invalid_field_characters[] attribute_hidden;
+
+_Bool __nss_valid_field (const char *value)
+  attribute_hidden internal_function;
+_Bool __nss_valid_list_field (char **list)
+  attribute_hidden internal_function;
+const char *__nss_rewrite_field (const char *value, char **to_be_freed)
+  attribute_hidden internal_function;
+
+#endif /* _NSS_H */