reverse: hide custom -config file located inside CIPHERDIR

In reverse mode, a custom config file passed via -config that lives inside
CIPHERDIR was presented as an ordinary encrypted file in the encrypted view,
which is useless and confusing. By default the config is mapped to a virtual
gocryptfs.conf, but ConfigCustom skips that mapping, so an in-CIPHERDIR custom
config was neither mapped nor hidden.

Plumb the config path into the reverse RootNode and treat a custom config file
located inside CIPHERDIR as excluded in isExcludedPlain, hiding it from both
readdir and lookup. Also document the -config reverse-mode behaviour in
MANPAGE.md and add a regression test.

Fixes #1009

1 files changed, 8 insertions, 0 deletions

diff --git a/Documentation/MANPAGE.md b/Documentation/MANPAGE.md
index 64bbaa8..3ef6500 100644
--- a/Documentation/MANPAGE.md
+++ b/Documentation/MANPAGE.md
@@ -457,6 +457,14 @@ Use specified config file instead of `CIPHERDIR/gocryptfs.conf`.
 
 Applies to: all actions that use a config file: mount, `-fsck`, `-passwd`, `-info`, `-init`.
 
+In `-reverse` mode, this also changes what the encrypted view contains: by
+default the config is exposed there as a virtual `gocryptfs.conf` (so a backup
+of the encrypted view is self-contained), but with `-config` no `gocryptfs.conf`
+is presented. Make sure to back up the config file (or the master key) from its
+custom location separately, otherwise the encrypted data cannot be decrypted.
+If the custom config file is located inside `CIPHERDIR`, it is hidden from the
+encrypted view rather than exposed in encrypted form.
+
 #### -cpuprofile string
 Write cpu profile to specified file.