[Libguestfs] [libguestfs-common PATCH 2/2] options: decrypt LUKS-on-LV devices

[Laszlo Ersek]

On 02/28/22 10:00, Richard W.M. Jones wrote:
> On Fri, Feb 25, 2022 at 11:59:37AM +0100, Laszlo Ersek wrote:
>> On 02/24/22 13:12, Laszlo Ersek wrote:
>>> On 02/24/22 11:43, Richard W.M. Jones wrote:
>>>> On Wed, Feb 23, 2022 at 05:19:15PM +0100, Laszlo Ersek wrote:
>>>>> Using the previously extracted function decrypt_mountables(), look for
>>>>> LUKS devices on logical volumes (LVs) too.
>>>>>
>>>>> In the LVM-on-LUKS scheme, the names of the plaintext (decrypted) block
>>>>> devices don't matter, as these devices host Physical Volumes, and LVM
>>>>> enumerates PVs automatically -- there are no references to these decrypted
>>>>> block devices in "/etc/fstab", for example. For naming such decrypted
>>>>> devices, continue calling make_mapname().
>>>>>
>>>>> In the LUKS-on-LVM scheme however, the decrypted devices are supposed to
>>>>> hold filesystems, and "/etc/fstab" may refer to them. Such decrypted
>>>>> devices are commonly called /dev/mapper/luks-<UUID>, where <UUID> is the
>>>>> UUID inside the LUKS header. Employ this naming when decrypting Logical
>>>>> Volumes. Reuse make_mapname() as a fallback in this case.
>>>>>
>>>>> Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=1658126
>>>>> Signed-off-by: Laszlo Ersek <lersek at redhat.com>
>>>>>
>>>>> Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=1658126
>>>>> Signed-off-by: Laszlo Ersek <lersek at redhat.com>
>>>>> ---
>>>>>  options/decrypt.c | 24 ++++++++++++++++++------
>>>>>  1 file changed, 18 insertions(+), 6 deletions(-)
>>>>>
>>>>> diff --git a/options/decrypt.c b/options/decrypt.c
>>>>> index 9141cf5193ad..f7c1d876b3ed 100644
>>>>> --- a/options/decrypt.c
>>>>> +++ b/options/decrypt.c
>>>>> @@ -38,8 +38,11 @@
>>>>>  #include "options.h"
>>>>>  
>>>>>  /**
>>>>> - * Make a LUKS map name from the partition name,
>>>>> - * eg. C<"/dev/vda2" =E<gt> "cryptvda2">
>>>>> + * Make a LUKS map name from the partition or logical volume name, eg.
>>>>> + * C<"/dev/vda2" =E<gt> "cryptvda2">, or C<"/dev/vg-ssd/lv-root7" =E<gt>
>>>>> + * "cryptvgssdlvroot7">.  Note that, in logical volume device names,
>>>>> + * c_isalnum() eliminates the "/" separator from between the VG and the LV, so
>>>>> + * this mapping is not unique; but for our purposes, it will do.
>>>>>   */
>>>>>  static void
>>>>>  make_mapname (const char *device, char *mapname, size_t len)
>>>>> @@ -67,7 +70,7 @@ make_mapname (const char *device, char *mapname, size_t len)
>>>>>  
>>>>>  static bool
>>>>>  decrypt_mountables (guestfs_h *g, const char * const *mountables,
>>>>> -                    struct key_store *ks)
>>>>> +                    struct key_store *ks, bool name_decrypted_by_uuid)
>>>>>  {
>>>>>    bool decrypted_some = false;
>>>>>    const char * const *mnt_scan = mountables;
>>>>> @@ -77,7 +80,7 @@ decrypt_mountables (guestfs_h *g, const char * const *mountables,
>>>>>      CLEANUP_FREE char *type = NULL;
>>>>>      CLEANUP_FREE char *uuid = NULL;
>>>>>      CLEANUP_FREE_STRING_LIST char **keys = NULL;
>>>>> -    char mapname[32];
>>>>> +    char mapname[512];
>>>>>      const char * const *key_scan;
>>>>>      const char *key;
>>>>>  
>>>>> @@ -102,7 +105,9 @@ decrypt_mountables (guestfs_h *g, const char * const *mountables,
>>>>>      assert (keys[0] != NULL);
>>>>>  
>>>>>      /* Generate a node name for the plaintext (decrypted) device node. */
>>>>> -    make_mapname (mountable, mapname, sizeof mapname);
>>>>> +    if (!name_decrypted_by_uuid || uuid == NULL ||
>>>>> +        snprintf (mapname, sizeof mapname, "luks-%s", uuid) < 0)
>>>>> +      make_mapname (mountable, mapname, sizeof mapname);
>>>>
>>>> This should all really be using asprintf, and not stack-allocating
>>>> large arrays.  Although it's kind of not related to this change, this
>>>> change does make the stack frame larger.
>>>
>>> asprintf() was my first idea, but reworking make_mapname() would then
>>> require measuring the input string lenght ;)
>>>
>>> OK, I'll insert a patch between #1 and #2 for converting make_mapname()
>>> to asprintf(), then I'll redo this patch with asprintf() too.
>>
>> On a second thought, if it's OK with you:
>>
>> I'd prefer merging this series as-is, and then posting additional
>> patches on top:
>>
>> - assume GUESTFS_HAVE_LUKS_UUID
>> - assume GUESTFS_HAVE_CRYPTSETUP_OPEN
>> - bump libguestfs version requirement in
>> virt-v2v.git/m4/guestfs-libraries.m4 to 1.44
>> - remove "XXX Should we set GUESTFS_CRYPTSETUP_OPEN_READONLY"
>> - allocate "mapname" with asprintf() on all paths.
>>
>> The reason I'd like to do these afterwards is that none of these warts
>> are introduced/created by this series, and I had put lots of testing
>> into the series (not just at the end, but mid-series too). If I rebased
>> and needed to resolved conflicts, all that testing would have to be
>> redone. I'd really like to avoid that.
> 
> That's fine.

Thanks!

Commit range 41126802097f..2d8c0f8d40b5 (for now).

Thanks,
Laszlo