From: Phil Pennock <pdp@exim.org>
Date: Tue, 15 May 2018 23:04:34 +0000 (-0400)
Subject: Don't open spool data-files which are symlinks
X-Git-Url: https://git.exim.org/users/jgh/exim.git/commitdiff_plain/85defcf0e9e4187107b8a1a5138ef9590ac3892c

Don't open spool data-files which are symlinks
---

diff --git a/doc/doc-txt/ChangeLog b/doc/doc-txt/ChangeLog
index d9b77804b..d99b2684a 100644
--- a/doc/doc-txt/ChangeLog
+++ b/doc/doc-txt/ChangeLog
@@ -29,6 +29,9 @@ JH/05 Bug 2273: Cutthrough delivery left a window where the received messsage
       add more error-checking on spoolfile handling while that code is being
       messed with.
 
+PP/01 Refuse to open a spool data file (*-D) if it's a symlink.
+      No known attacks, no CVE, this is defensive hardening.
+
 
 Exim version 4.91
 -----------------
diff --git a/src/src/spool_in.c b/src/src/spool_in.c
index 33890c516..cd74d1ee7 100644
--- a/src/src/spool_in.c
+++ b/src/src/spool_in.c
@@ -57,9 +57,17 @@ for (i = 0; i < 2; i++)
   fname = spool_fname(US"input", message_subdir, id, US"-D");
   DEBUG(D_deliver) debug_printf("Trying spool file %s\n", fname);
 
+  /* We protect against symlink attacks both in not propagating the
+   * file-descriptor to other processes as we exec, and also ensuring that we
+   * don't even open symlinks.
+   * No -D file inside the spool area should be a symlink.
+   */
   if ((fd = Uopen(fname,
 #ifdef O_CLOEXEC
 		      O_CLOEXEC |
+#endif
+#ifdef O_NOFOLLOW
+		      O_NOFOLLOW |
 #endif
 		      O_RDWR | O_APPEND, 0)) >= 0)
     break;