From bde493349025ca0559e2fff88592935af3b8df19 Mon Sep 17 00:00:00 2001 From: Eric Biggers Date: Fri, 13 Nov 2020 13:19:18 -0800 Subject: fs-verity: move structs needed for file signing to UAPI header Although it isn't used directly by the ioctls, "struct fsverity_descriptor" is required by userspace programs that need to compute fs-verity file digests in a standalone way. Therefore it's also needed to sign files in a standalone way. Similarly, "struct fsverity_formatted_digest" (previously called "struct fsverity_signed_digest" which was misleading) is also needed to sign files if the built-in signature verification is being used. Therefore, move these structs to the UAPI header. While doing this, try to make it clear that the signature-related fields in fsverity_descriptor aren't used in the file digest computation. Acked-by: Luca Boccassi Link: https://lore.kernel.org/r/20201113211918.71883-5-ebiggers@kernel.org Signed-off-by: Eric Biggers --- include/uapi/linux/fsverity.h | 49 +++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 49 insertions(+) (limited to 'include/uapi') diff --git a/include/uapi/linux/fsverity.h b/include/uapi/linux/fsverity.h index da0daf6c193b..33f44156f8ea 100644 --- a/include/uapi/linux/fsverity.h +++ b/include/uapi/linux/fsverity.h @@ -34,6 +34,55 @@ struct fsverity_digest { __u8 digest[]; }; +/* + * Struct containing a file's Merkle tree properties. The fs-verity file digest + * is the hash of this struct. A userspace program needs this struct only if it + * needs to compute fs-verity file digests itself, e.g. in order to sign files. + * It isn't needed just to enable fs-verity on a file. + * + * Note: when computing the file digest, 'sig_size' and 'signature' must be left + * zero and empty, respectively. These fields are present only because some + * filesystems reuse this struct as part of their on-disk format. + */ +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 */ +#ifdef __KERNEL__ + __le32 sig_size; +#else + __le32 __reserved_0x04; /* must be 0 */ +#endif + __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 */ +#ifdef __KERNEL__ + __u8 signature[]; +#endif +}; + +/* + * Format in which fs-verity file digests are signed in built-in signatures. + * This is the same as 'struct fsverity_digest', except here some magic bytes + * are prepended to provide some context about what is being signed in case the + * same key is used for non-fsverity purposes, and here the fields have fixed + * endianness. + * + * This struct is specific to the built-in signature verification support, which + * is optional. fs-verity users may also verify signatures in userspace, in + * which case userspace is responsible for deciding on what bytes are signed. + * This struct may still be used, but it doesn't have to be. For example, + * userspace could instead use a string like "sha256:$digest_as_hex_string". + */ +struct fsverity_formatted_digest { + char magic[8]; /* must be "FSVerity" */ + __le16 digest_algorithm; + __le16 digest_size; + __u8 digest[]; +}; + #define FS_IOC_ENABLE_VERITY _IOW('f', 133, struct fsverity_enable_arg) #define FS_IOC_MEASURE_VERITY _IOWR('f', 134, struct fsverity_digest) -- cgit v1.2.3