Re: [RFC PATCH v3 07/18] fscrypt: add FS_IOC_ADD_ENCRYPTION_KEY ioctl

On Thu, Feb 21, 2019 at 10:33:12AM +0100, Richard Weinberger wrote:

Eric,

Am Donnerstag, 21. Februar 2019, 06:49:39 CET schrieb Eric Biggers:

quoted

Hi Richard,

On Thu, Feb 21, 2019 at 12:52:38AM +0100, Richard Weinberger wrote:

quoted

On Wed, Feb 20, 2019 at 7:55 AM Eric Biggers [off-list ref] wrote:

quoted

+#define FSCRYPT_FS_KEYRING_DESCRIPTION_SIZE    \
+       (CONST_STRLEN("fscrypt-") + FIELD_SIZEOF(struct super_block, s_id))
+
+#define FSCRYPT_MK_DESCRIPTION_SIZE    (2 * FSCRYPT_KEY_DESCRIPTOR_SIZE + 1)
+
+static void format_fs_keyring_description(
+                       char description[FSCRYPT_FS_KEYRING_DESCRIPTION_SIZE],
+                       const struct super_block *sb)
+{
+       sprintf(description, "fscrypt-%s", sb->s_id);
+}

I fear ->s_id is not the right thing.
For filesystems such as ext4 ->s_id is the name of the backing block device,
so it is per filesysem instance unique.
But this is not guaranteed. For UBIFS ->s_id is just "ubifs", always.
So the names will clash.

What name do you suggest using for UBIFS filesystems?  The keyring name could be
set by the filesystem via a fscrypt_operations callback if needed.

IMHO the BDI name should be used. 

quoted

Note that the keyring name isn't particularly important, since the ioctls will
work regardless.  But we might as well choose something logical, since the
keyring name will still show up in /proc/keys.

I'm not done with reviewing your patches, but will it be possible to use keyctl?
For the a unique name is helpful. :)

Not for adding keys, removing keys, or getting a key's status -- those are what
the ioctls are for.

See e.g. the discussion in patch 7 ("fscrypt: add FS_IOC_ADD_ENCRYPTION_KEY
ioctl") for why the keyrings syscalls are a poor fit for fscrypt.

- Eric