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cryptsetup: Implement offset and skip options 

These are useful for plain devices as they don't have any metadata by
themselves. Instead of using an unreliable hardcoded device name in crypttab
you can then put static metadata at the start of the partition for a stable
UUID or label.

https://bugs.freedesktop.org/show_bug.cgi?id=87717
https://bugs.debian.org/751707
https://launchpad.net/bugs/953875
This commit is contained in:
Martin Pitt 2015-04-16 06:44:07 -05:00
parent 18ae3d98d9
commit 4eac277367
2 changed files with 52 additions and 3 deletions
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24
man/crypttab.xml
View File

@ -145,6 +145,30 @@
option.</para></listitem>
</varlistentry>
<varlistentry>
<term><option>offset=</option></term>
<listitem><para>Start offset in the backend device, in 512-byte sectors.
This option is only relevant for plain devices.
</para></listitem>
</varlistentry>
<varlistentry>
<term><option>skip=</option></term>
<listitem><para>How many 512-byte sectors of the encrypted data to skip
at the beginning. This is different from the <option>--offset</option>
option with respect to the sector numbers used in initialization vector
(IV) calculation. Using <option>--offset</option> will shift the IV
calculation by the same negative amount. Hence, if <option>--offset n</option>,
sector n will get a sector number of 0 for the IV calculation.
Using <option>--skip</option> causes sector n to also be the first
sector of the mapped device, but with its number for IV generation is n.</para>
<para>This option is only relevant for plain devices.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>keyfile-offset=</option></term>

31
src/cryptsetup/cryptsetup.c
View File

@ -50,12 +50,12 @@ static bool arg_discards = false;
static bool arg_tcrypt_hidden = false;
static bool arg_tcrypt_system = false;
static char **arg_tcrypt_keyfiles = NULL;
static uint64_t arg_offset = 0;
static uint64_t arg_skip = 0;
static usec_t arg_timeout = 0;
/* Options Debian's crypttab knows we don't:
offset=
skip=
precheck=
check=
checkargs=
@ -185,6 +185,20 @@ static int parse_one_option(const char *option) {
return 0;
}
} else if (startswith(option, "offset=")) {
if (safe_atou64(option+7, &arg_offset) < 0) {
log_error("offset= parse failure, refusing.");
return -EINVAL;
}
} else if (startswith(option, "skip=")) {
if (safe_atou64(option+5, &arg_skip) < 0) {
log_error("skip= parse failure, refusing.");
return -EINVAL;
}
} else if (!streq(option, "none"))
log_error("Encountered unknown /etc/crypttab option '%s', ignoring.", option);
@ -209,6 +223,14 @@ static int parse_options(const char *options) {
return r;
}
/* sanity-check options */
if (arg_type != NULL && !streq(arg_type, CRYPT_PLAIN)) {
if (arg_offset)
log_warning("offset= ignored with type %s", arg_type);
if (arg_skip)
log_warning("skip= ignored with type %s", arg_type);
}
return 0;
}
@ -410,7 +432,10 @@ static int attach_luks_or_plain(struct crypt_device *cd,
}
if ((!arg_type && r < 0) || streq_ptr(arg_type, CRYPT_PLAIN)) {
struct crypt_params_plain params = {};
struct crypt_params_plain params = {
.offset = arg_offset,
.skip = arg_skip,
};
const char *cipher, *cipher_mode;
_cleanup_free_ char *truncated_cipher = NULL;