Re: [RFC PATCH v3 08/16] ceph: implement -o test_dummy_encryption mount option

Jeff Layton
2020-09-16T17:52:20Z

On Mon, 2020-09-14 at 18:23 -0700, Eric Biggers wrote:
> On Mon, Sep 14, 2020 at 03:16:59PM -0400, Jeff Layton wrote:
> > + case Opt_test_dummy_encryption:
> > + kfree(fsopt->test_dummy_encryption);
> > +#ifdef CONFIG_FS_ENCRYPTION
> > + fsopt->test_dummy_encryption = param->string;
> > + param->string = NULL;
> > + fsopt->flags |= CEPH_MOUNT_OPT_TEST_DUMMY_ENC;
> > +#else
> > + warnfc(fc, "FS encryption not supported: test_dummy_encryption mount option ignored");
> > +#endif
>
> Seems that the kfree() should go in the CONFIG_FS_ENCRYPTION=y block.
>
> Also, is there much reason to have the CEPH_MOUNT_OPT_TEST_DUMMY_ENC flag
> instead of just checking fsopt->test_dummy_encryption != NULL?
>

Yes. That distinguishes between the case where someone has used
-o test_dummy_encryption and -o test_dummy_encryption=v2.

> > +#ifdef CONFIG_FS_ENCRYPTION
> > +static int ceph_set_test_dummy_encryption(struct super_block *sb, struct fs_context *fc,
> > + struct ceph_mount_options *fsopt)
> > +{
> > + struct ceph_fs_client *fsc = sb->s_fs_info;
> > +
> > + if (fsopt->flags & CEPH_MOUNT_OPT_TEST_DUMMY_ENC) {
> > + substring_t arg = { };
> > +
> > + /*
> > + * No changing encryption context on remount. Note that
> > + * fscrypt_set_test_dummy_encryption will validate the version
> > + * string passed in (if any).
> > + */
> > + if (fc->purpose == FS_CONTEXT_FOR_RECONFIGURE && !fsc->dummy_enc_policy.policy)
> > + return -EEXIST;
>
> Maybe show an error message here, with errorfc()?
> See the message that ext4_set_test_dummy_encryption() shows.
>

Good idea. I've rolled in error messages similar to the ones in ext4.

> > +
> > + /* Ewwwwwwww */
> > + if (fsc->mount_options->test_dummy_encryption) {
> > + arg.from = fsc->mount_options->test_dummy_encryption;
> > + arg.to = arg.from + strlen(arg.from) - 1;
> > + }
>
> We should probably make fscrypt_set_test_dummy_encryption() take a
> 'const char *' to avoid having to create a substring_t here.
>

Yes, please. I didn't want to do that with most of the current fscrypt-
enabled fs using the old mount API. Some of them may need to copy the
argument so that it's properly terminated.

We could also just add a wrapper that turns the const char * into a
substring_t before calling fscrypt_set_test_dummy_encryption.

> > + return fscrypt_set_test_dummy_encryption(sb, &arg, &fsc->dummy_enc_policy);
>
> Likewise, maybe show an error message if this fails.
>
> > + } else {
> > + if (fc->purpose == FS_CONTEXT_FOR_RECONFIGURE && fsc->dummy_enc_policy.policy)
> > + return -EEXIST;
>
> If remount on ceph behaves as "don't change options that aren't specified",
> similar to ext4, then there's no need for this hunk here.
>

Good point.

> > static int ceph_reconfigure_fc(struct fs_context *fc)
> > {
> > + int err;
> > struct ceph_parse_opts_ctx *pctx = fc->fs_private;
> > struct ceph_mount_options *fsopt = pctx->opts;
> > - struct ceph_fs_client *fsc = ceph_sb_to_client(fc->root->d_sb);
> > + struct super_block *sb = fc->root->d_sb;
> > + struct ceph_fs_client *fsc = ceph_sb_to_client(sb);
> >
> > if (fsopt->flags & CEPH_MOUNT_OPT_ASYNC_DIROPS)
> > ceph_set_mount_opt(fsc, ASYNC_DIROPS);
> > else
> > ceph_clear_mount_opt(fsc, ASYNC_DIROPS);
> >
> > - sync_filesystem(fc->root->d_sb);
> > + err = ceph_set_test_dummy_encryption(sb, fc, fsopt);
> > + if (err)
> > + return err;
> > +
> > + sync_filesystem(sb);
> > return 0;
> > }
>
> Seems that ceph_set_test_dummy_encryption() should go at the beginning, since
> otherwise it can fail after something was already changed.
>

Good catch. Fixed.

--
Jeff Layton <jlayton@kernel.org>