e2fsck: Make the -n always open the file system read-only

A user was surprised when -n -D caused the file system to be opened
read/write, and then outsmarted himself when e2fsck asked the question:

   WARNING!!!  Running e2fsck on a mounted filesystem may cause
   SEVERE filesystem damage.

   Do you really want to continue (y/n)?

This is partially our fault for not documenting the fact that -D
overrode opening the filesystem read-write.  But the bottom line is it
much safer if -n *always* opens the file system read-only, so there
can be no confusion.  This means that we have to disable certain
combination of options, such as "-n -c", "-n -l", and "-n -L", and
"-n -D", but the utility of these combinations is pretty low, and
is more than offset by making e2fsck idiot-proof.

Addresses-Launchpad-Bug: #537483

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

1 files changed, 17 insertions, 2 deletions

diff --git a/e2fsck/unix.c b/e2fsck/unix.c
index 62489580..49e90085 100644
--- a/e2fsck/unix.c
+++ b/e2fsck/unix.c
@@ -789,8 +789,23 @@ static errcode_t PRS(int argc, char *argv[], e2fsck_t *ret_ctx)
 		return 0;
 	if (optind != argc - 1)
 		usage(ctx);
-	if ((ctx->options & E2F_OPT_NO) && !bad_blocks_file &&
-	    !cflag && !(ctx->options & E2F_OPT_COMPRESS_DIRS))
+	if ((ctx->options & E2F_OPT_NO) &&
+	    (ctx->options & E2F_OPT_COMPRESS_DIRS)) {
+		com_err(ctx->program_name, 0,
+			_("The -n and -D options are incompatible."));
+		fatal_error(ctx, 0);
+	}
+	if ((ctx->options & E2F_OPT_NO) && cflag) {
+		com_err(ctx->program_name, 0,
+			_("The -n and -c options are incompatible."));
+		fatal_error(ctx, 0);
+	}
+	if ((ctx->options & E2F_OPT_NO) && bad_blocks_file) {
+		com_err(ctx->program_name, 0,
+			_("The -n and -l/-L options are incompatible."));
+		fatal_error(ctx, 0);
+	}
+	if (ctx->options & E2F_OPT_NO)
 		ctx->options |= E2F_OPT_READONLY;
 
 	ctx->io_options = strchr(argv[optind], '?');