On Tue, Apr 21, 2020 at 12:07:07PM -0400, Jes Sorensen wrote:
> On 3/22/20 12:57 AM, Eric Biggers wrote:
> > On Thu, Mar 12, 2020 at 05:47:52PM -0400, Jes Sorensen wrote:
> >> From: Jes Sorensen <jsorensen@xxxxxx>
> >>
> >> Signed-off-by: Jes Sorensen <jsorensen@xxxxxx>
> >> ---
> >> cmd_sign.c | 19 +------------------
> >> libfsverity.h | 26 +++++++++++++++++++++++++-
> >> 2 files changed, 26 insertions(+), 19 deletions(-)
> >>
> >> diff --git a/cmd_sign.c b/cmd_sign.c
> >> index dcc44f8..1792084 100644
> >> --- a/cmd_sign.c
> >> +++ b/cmd_sign.c
> >> @@ -20,26 +20,9 @@
> >> #include <unistd.h>
> >>
> >> #include "commands.h"
> >> -#include "fsverity_uapi.h"
> >> +#include "libfsverity.h"
> >> #include "hash_algs.h"
> >>
> >> -/*
> >> - * Merkle tree properties. The file measurement is the hash of this structure
> >> - * excluding the signature and with the sig_size field set to 0.
> >> - */
> >> -struct fsverity_descriptor {
> >> - __u8 version; /* must be 1 */
> >> - __u8 hash_algorithm; /* Merkle tree hash algorithm */
> >> - __u8 log_blocksize; /* log2 of size of data and tree blocks */
> >> - __u8 salt_size; /* size of salt in bytes; 0 if none */
> >> - __le32 sig_size; /* size of signature in bytes; 0 if none */
> >> - __le64 data_size; /* size of file the Merkle tree is built over */
> >> - __u8 root_hash[64]; /* Merkle tree root hash */
> >> - __u8 salt[32]; /* salt prepended to each hashed block */
> >> - __u8 __reserved[144]; /* must be 0's */
> >> - __u8 signature[]; /* optional PKCS#7 signature */
> >> -};
> >> -
> >> /*
> >> * Format in which verity file measurements are signed. This is the same as
> >> * 'struct fsverity_digest', except here some magic bytes are prepended to
> >> diff --git a/libfsverity.h b/libfsverity.h
> >> index ceebae1..396a6ee 100644
> >> --- a/libfsverity.h
> >> +++ b/libfsverity.h
> >> @@ -13,13 +13,14 @@
> >>
> >> #include <stddef.h>
> >> #include <stdint.h>
> >> +#include <linux/types.h>
> >>
> >> #define FS_VERITY_HASH_ALG_SHA256 1
> >> #define FS_VERITY_HASH_ALG_SHA512 2
> >>
> >> struct libfsverity_merkle_tree_params {
> >> uint16_t version;
> >> - uint16_t hash_algorithm;
> >> + uint16_t hash_algorithm; /* Matches the digest_algorithm type */
> >> uint32_t block_size;
> >> uint32_t salt_size;
> >> const uint8_t *salt;
> >> @@ -27,6 +28,7 @@ struct libfsverity_merkle_tree_params {
> >> };
> >>
> >> struct libfsverity_digest {
> >> + char magic[8]; /* must be "FSVerity" */
> >> uint16_t digest_algorithm;
> >> uint16_t digest_size;
> >> uint8_t digest[];
> >> @@ -38,4 +40,26 @@ struct libfsverity_signature_params {
> >> uint64_t reserved[11];
> >> };
> >>
> >> +/*
> >> + * Merkle tree properties. The file measurement is the hash of this structure
> >> + * excluding the signature and with the sig_size field set to 0.
> >> + */
> >> +struct fsverity_descriptor {
> >> + uint8_t version; /* must be 1 */
> >> + uint8_t hash_algorithm; /* Merkle tree hash algorithm */
> >> + uint8_t log_blocksize; /* log2 of size of data and tree blocks */
> >> + uint8_t salt_size; /* size of salt in bytes; 0 if none */
> >> + __le32 sig_size; /* size of signature in bytes; 0 if none */
> >> + __le64 data_size; /* size of file the Merkle tree is built over */
> >> + uint8_t root_hash[64]; /* Merkle tree root hash */
> >> + uint8_t salt[32]; /* salt prepended to each hashed block */
> >> + uint8_t __reserved[144];/* must be 0's */
> >> + uint8_t signature[]; /* optional PKCS#7 signature */
> >> +};
> >> +
> >
> > I thought there was no need for this to be part of the library API?
>
> Hi Eric,
>
> Been busy working on RPM support, but looking at this again now. Given
> that the fsverity signature is a hash of the descriptor, I don't see how
> we can avoid this?
>
struct fsverity_descriptor isn't signed directly; it's hashed as an intermediate
step in libfsverity_compute_digest(). So why would the library user need the
definition of 'struct fsverity_descriptor'?
- Eric
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