patch 9.0.1968: cmdline completion should consider key optionv9.0.1968

Problem:  cmdline completion should consider key option
Solution: Disable cmdline completion for key option, slightly
          refactor how P_NO_CMD_EXPAND is handled

Harden crypto 'key' option: turn off cmdline completion, disable set-=

"set-=" can be used maliciously with a crypto key, as it allows an
attacker (who either has access to the computer or a plugin author) to
guess a substring by observing the modified state. Simply turn off
set+=/-=/^= for this option as there is no good reason for them to be
used.

Update docs to make that clear as well.

Also, don't allow cmdline completion for 'key' as it just shows *****
which is not useful and confusing to the user what it means (if the user
accidentally hits enter they will have replaced their key with "*****"
instead).

Move logic to better location, don't use above 32-bit for flags

Move P_NO_CMD_EXPAND to use the unused 0x20 instead of going above
32-bits, as currently the flags parameter is only 32-bits on some
systems. Left a comment to warn that future additions will need to
change how the flags work either by making it 64-bit or split into two
member vars.

Also, move the logic for detecting P_NO_CMD_EXPAND earlier so it's not
up to each handler to decide, and you won't see the temporary "..." that
Vim shows while waiting for completion handler to complete.

closes: #13224

Signed-off-by: Christian Brabandt <cb@256bit.org>
Co-authored-by: Yee Cheng Chin <ychin.git@gmail.com>

1 files changed, 7 insertions, 1 deletions

diff --git a/src/optionstr.c b/src/optionstr.c
index 88532ee599..5a3dd6e758 100644
--- a/src/optionstr.c
+++ b/src/optionstr.c
@@ -579,7 +579,7 @@ set_string_option(
     }
 #endif
     if ((errmsg = did_set_string_option(opt_idx, varp, oldval, value, errbuf,
-		    opt_flags, &value_checked)) == NULL)
+		    opt_flags, OP_NONE, &value_checked)) == NULL)
 	did_set_option(opt_idx, opt_flags, TRUE, value_checked);
 
 #if defined(FEAT_EVAL)
@@ -1578,6 +1578,10 @@ did_set_cryptkey(optset_T *args)
     // history.
     remove_key_from_history();
 
+    if (args->os_op != OP_NONE)
+	// Don't allow set+=/-=/^= as they can allow for substring guessing
+	return e_invalid_argument;
+
     if (STRCMP(curbuf->b_p_key, args->os_oldval.string) != 0)
     {
 	// Need to update the swapfile.
@@ -4209,6 +4213,7 @@ did_set_string_option(
     char_u	*value,			// new value of the option
     char	*errbuf,		// buffer for errors, or NULL
     int		opt_flags,		// OPT_LOCAL and/or OPT_GLOBAL
+    set_op_T    op,			// OP_ADDING/OP_PREPENDING/OP_REMOVING
     int		*value_checked)		// value was checked to be safe, no
 					// need to set P_INSECURE
 {
@@ -4247,6 +4252,7 @@ did_set_string_option(
 	args.os_varp = (char_u *)varp;
 	args.os_idx = opt_idx;
 	args.os_flags = opt_flags;
+	args.os_op = op;
 	args.os_oldval.string = oldval;
 	args.os_newval.string = value;
 	args.os_errbuf = errbuf;