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[v3,3/5] fscrypt: compute max_lblk_bits from s_maxbytes and block size

Message ID 20230925055451.59499-4-ebiggers@kernel.org (mailing list archive)
State New, archived
Headers show
Series fscrypt: add support for data_unit_size < fs_block_size | expand

Commit Message

Eric Biggers Sept. 25, 2023, 5:54 a.m. UTC 
From: Eric Biggers <ebiggers@google.com>

For a given filesystem, the number of bits used by the maximum file
logical block number is computable from the maximum file size and block
size.  These values are always present in struct super_block.
Therefore, compute it this way instead of using the value from
fscrypt_operations::get_ino_and_lblk_bits.  Since filesystems always
have to set the super_block fields anyway, this avoids having to provide
this information redundantly via fscrypt_operations.

This change is in preparation for adding support for sub-block data
units.  For that, the value that is needed will become "the maximum file
data unit index".  A hardcoded value won't suffice for that; it will
need to be computed anyway.

Signed-off-by: Eric Biggers <ebiggers@google.com>
---
 fs/crypto/fscrypt_private.h | 10 ++++++++++
 fs/crypto/inline_crypt.c    |  7 ++-----
 fs/crypto/policy.c          | 18 ++++++++++--------
 3 files changed, 22 insertions(+), 13 deletions(-)
diff mbox series

Patch

diff --git a/fs/crypto/fscrypt_private.h b/fs/crypto/fscrypt_private.h
index 2d63da48635ab..4b113214b53af 100644
--- a/fs/crypto/fscrypt_private.h
+++ b/fs/crypto/fscrypt_private.h
@@ -289,20 +289,30 @@  union fscrypt_iv {
 		/* per-file nonce; only set in DIRECT_KEY mode */
 		u8 nonce[FSCRYPT_FILE_NONCE_SIZE];
 	};
 	u8 raw[FSCRYPT_MAX_IV_SIZE];
 	__le64 dun[FSCRYPT_MAX_IV_SIZE / sizeof(__le64)];
 };
 
 void fscrypt_generate_iv(union fscrypt_iv *iv, u64 lblk_num,
 			 const struct fscrypt_info *ci);
 
+/*
+ * Return the number of bits used by the maximum file logical block number that
+ * is possible on the given filesystem.
+ */
+static inline int
+fscrypt_max_file_lblk_bits(const struct super_block *sb)
+{
+	return fls64(sb->s_maxbytes - 1) - sb->s_blocksize_bits;
+}
+
 /* fname.c */
 bool __fscrypt_fname_encrypted_size(const union fscrypt_policy *policy,
 				    u32 orig_len, u32 max_len,
 				    u32 *encrypted_len_ret);
 
 /* hkdf.c */
 struct fscrypt_hkdf {
 	struct crypto_shash *hmac_tfm;
 };
 
diff --git a/fs/crypto/inline_crypt.c b/fs/crypto/inline_crypt.c
index 8bfb3ce864766..7d9f6c167de58 100644
--- a/fs/crypto/inline_crypt.c
+++ b/fs/crypto/inline_crypt.c
@@ -34,37 +34,34 @@  static struct block_device **fscrypt_get_devices(struct super_block *sb,
 	devs = kmalloc(sizeof(*devs), GFP_KERNEL);
 	if (!devs)
 		return ERR_PTR(-ENOMEM);
 	devs[0] = sb->s_bdev;
 	*num_devs = 1;
 	return devs;
 }
 
 static unsigned int fscrypt_get_dun_bytes(const struct fscrypt_info *ci)
 {
-	struct super_block *sb = ci->ci_inode->i_sb;
+	const struct super_block *sb = ci->ci_inode->i_sb;
 	unsigned int flags = fscrypt_policy_flags(&ci->ci_policy);
-	int ino_bits = 64, lblk_bits = 64;
 
 	if (flags & FSCRYPT_POLICY_FLAG_DIRECT_KEY)
 		return offsetofend(union fscrypt_iv, nonce);
 
 	if (flags & FSCRYPT_POLICY_FLAG_IV_INO_LBLK_64)
 		return sizeof(__le64);
 
 	if (flags & FSCRYPT_POLICY_FLAG_IV_INO_LBLK_32)
 		return sizeof(__le32);
 
 	/* Default case: IVs are just the file logical block number */
-	if (sb->s_cop->get_ino_and_lblk_bits)
-		sb->s_cop->get_ino_and_lblk_bits(sb, &ino_bits, &lblk_bits);
-	return DIV_ROUND_UP(lblk_bits, 8);
+	return DIV_ROUND_UP(fscrypt_max_file_lblk_bits(sb), 8);
 }
 
 /*
  * Log a message when starting to use blk-crypto (native) or blk-crypto-fallback
  * for an encryption mode for the first time.  This is the blk-crypto
  * counterpart to the message logged when starting to use the crypto API for the
  * first time.  A limitation is that these messages don't convey which specific
  * filesystems or files are using each implementation.  However, *usually*
  * systems use just one implementation per mode, which makes these messages
  * helpful for debugging problems where the "wrong" implementation is used.
diff --git a/fs/crypto/policy.c b/fs/crypto/policy.c
index f4456ecb3f877..7b34949e49de6 100644
--- a/fs/crypto/policy.c
+++ b/fs/crypto/policy.c
@@ -112,22 +112,21 @@  static bool supported_direct_key_modes(const struct inode *inode,
 	if (mode->ivsize < offsetofend(union fscrypt_iv, nonce)) {
 		fscrypt_warn(inode, "Direct key flag not allowed with %s",
 			     mode->friendly_name);
 		return false;
 	}
 	return true;
 }
 
 static bool supported_iv_ino_lblk_policy(const struct fscrypt_policy_v2 *policy,
 					 const struct inode *inode,
-					 const char *type,
-					 int max_ino_bits, int max_lblk_bits)
+					 const char *type, int max_ino_bits)
 {
 	struct super_block *sb = inode->i_sb;
 	int ino_bits = 64, lblk_bits = 64;
 
 	/*
 	 * IV_INO_LBLK_* exist only because of hardware limitations, and
 	 * currently the only known use case for them involves AES-256-XTS.
 	 * That's also all we test currently.  For these reasons, for now only
 	 * allow AES-256-XTS here.  This can be relaxed later if a use case for
 	 * IV_INO_LBLK_* with other encryption modes arises.
@@ -151,23 +150,28 @@  static bool supported_iv_ino_lblk_policy(const struct fscrypt_policy_v2 *policy,
 		return false;
 	}
 	if (sb->s_cop->get_ino_and_lblk_bits)
 		sb->s_cop->get_ino_and_lblk_bits(sb, &ino_bits, &lblk_bits);
 	if (ino_bits > max_ino_bits) {
 		fscrypt_warn(inode,
 			     "Can't use %s policy on filesystem '%s' because its inode numbers are too long",
 			     type, sb->s_id);
 		return false;
 	}
-	if (lblk_bits > max_lblk_bits) {
+
+	/*
+	 * IV_INO_LBLK_64 and IV_INO_LBLK_32 both require that file logical
+	 * block numbers fit in 32 bits.
+	 */
+	if (fscrypt_max_file_lblk_bits(sb) > 32) {
 		fscrypt_warn(inode,
-			     "Can't use %s policy on filesystem '%s' because its block numbers are too long",
+			     "Can't use %s policy on filesystem '%s' because its maximum file size is too large",
 			     type, sb->s_id);
 		return false;
 	}
 	return true;
 }
 
 static bool fscrypt_supported_v1_policy(const struct fscrypt_policy_v1 *policy,
 					const struct inode *inode)
 {
 	if (!fscrypt_valid_enc_modes_v1(policy->contents_encryption_mode,
@@ -232,33 +236,31 @@  static bool fscrypt_supported_v2_policy(const struct fscrypt_policy_v2 *policy,
 			     policy->flags);
 		return false;
 	}
 
 	if ((policy->flags & FSCRYPT_POLICY_FLAG_DIRECT_KEY) &&
 	    !supported_direct_key_modes(inode, policy->contents_encryption_mode,
 					policy->filenames_encryption_mode))
 		return false;
 
 	if ((policy->flags & FSCRYPT_POLICY_FLAG_IV_INO_LBLK_64) &&
-	    !supported_iv_ino_lblk_policy(policy, inode, "IV_INO_LBLK_64",
-					  32, 32))
+	    !supported_iv_ino_lblk_policy(policy, inode, "IV_INO_LBLK_64", 32))
 		return false;
 
 	/*
 	 * IV_INO_LBLK_32 hashes the inode number, so in principle it can
 	 * support any ino_bits.  However, currently the inode number is gotten
 	 * from inode::i_ino which is 'unsigned long'.  So for now the
 	 * implementation limit is 32 bits.
 	 */
 	if ((policy->flags & FSCRYPT_POLICY_FLAG_IV_INO_LBLK_32) &&
-	    !supported_iv_ino_lblk_policy(policy, inode, "IV_INO_LBLK_32",
-					  32, 32))
+	    !supported_iv_ino_lblk_policy(policy, inode, "IV_INO_LBLK_32", 32))
 		return false;
 
 	if (memchr_inv(policy->__reserved, 0, sizeof(policy->__reserved))) {
 		fscrypt_warn(inode, "Reserved bits set in encryption policy");
 		return false;
 	}
 
 	return true;
 }