[PATCH v3 02/16] fscrypt: factor getting info for a specific block

[Sweet Tea Dorminy <sweettea-kernel@dorminy.me>]

For filesystems using extent-based encryption, the content of each
extent will be encrypted with a different fscrypt_info for each extent.
Meanwhile, directories and symlinks will continue to use the
fscrypt_info for the inode. Therefore, merely grabbing
inode->i_crypt_info will be insufficient; the caller must specifically
request the inode info or the info for a specific block.

Add fscrypt_get_lblk_info() to get info for a specific block, and update
all relevant callsites.

Signed-off-by: Sweet Tea Dorminy <sweettea-kernel@dorminy.me>
---
 fs/crypto/crypto.c          |  3 ++-
 fs/crypto/fscrypt_private.h | 29 +++++++++++++++++++++++++++++
 fs/crypto/inline_crypt.c    | 10 ++++++----
 3 files changed, 37 insertions(+), 5 deletions(-)

diff --git a/fs/crypto/crypto.c b/fs/crypto/crypto.c
index 9f3bda18c797..1b7e375b1c6b 100644
--- a/fs/crypto/crypto.c
+++ b/fs/crypto/crypto.c
@@ -107,7 +107,8 @@ int fscrypt_crypt_block(const struct inode *inode, fscrypt_direction_t rw,
 	struct skcipher_request *req = NULL;
 	DECLARE_CRYPTO_WAIT(wait);
 	struct scatterlist dst, src;
-	struct fscrypt_info *ci = inode->i_crypt_info;
+	struct fscrypt_info *ci =
+		fscrypt_get_lblk_info(inode, lblk_num, NULL, NULL);
 	struct crypto_skcipher *tfm = ci->ci_enc_key->tfm;
 	int res = 0;
 
diff --git a/fs/crypto/fscrypt_private.h b/fs/crypto/fscrypt_private.h
index e2acd8894ea7..8a1fd1d33cfc 100644
--- a/fs/crypto/fscrypt_private.h
+++ b/fs/crypto/fscrypt_private.h
@@ -277,6 +277,35 @@ typedef enum {
 	FS_ENCRYPT,
 } fscrypt_direction_t;
 
+/**
+ * fscrypt_get_lblk_info() - get the fscrypt_info to crypt a particular block
+ *
+ * @inode:      the inode to which the block belongs
+ * @lblk:       the offset of the block within the file which the inode
+ *              references
+ * @offset:     a pointer to return the offset of the block from the first block
+ *              that the info covers. For inode-based encryption, this will
+ *              always be @lblk; for extent-based encryption, this will be in
+ *              the range [0, lblk]. Can be NULL
+ * @extent_len: a pointer to return the minimum number of lblks starting at
+ *              this offset which also belong to the same fscrypt_info. Can be
+ *              NULL
+ *
+ * Return: the appropriate fscrypt_info if there is one, else NULL.
+ */
+static inline struct fscrypt_info *
+fscrypt_get_lblk_info(const struct inode *inode, u64 lblk, u64 *offset,
+		      u64 *extent_len)
+{
+	if (offset)
+		*offset = lblk;
+	if (extent_len)
+		*extent_len = U64_MAX;
+
+	return inode->i_crypt_info;
+}
+
+
 /* crypto.c */
 extern struct kmem_cache *fscrypt_info_cachep;
 int fscrypt_initialize(struct super_block *sb);
diff --git a/fs/crypto/inline_crypt.c b/fs/crypto/inline_crypt.c
index 2063f7941ce6..885a2ec3d711 100644
--- a/fs/crypto/inline_crypt.c
+++ b/fs/crypto/inline_crypt.c
@@ -270,7 +270,7 @@ void fscrypt_set_bio_crypt_ctx(struct bio *bio, const struct inode *inode,
 
 	if (!fscrypt_inode_uses_inline_crypto(inode))
 		return;
-	ci = inode->i_crypt_info;
+	ci = fscrypt_get_lblk_info(inode, first_lblk, NULL, NULL);
 
 	fscrypt_generate_dun(ci, first_lblk, dun);
 	bio_crypt_set_ctx(bio, ci->ci_enc_key->blk_key, dun, gfp_mask);
@@ -349,21 +349,23 @@ bool fscrypt_mergeable_bio(struct bio *bio, const struct inode *inode,
 {
 	const struct bio_crypt_ctx *bc = bio->bi_crypt_context;
 	u64 next_dun[BLK_CRYPTO_DUN_ARRAY_SIZE];
+	struct fscrypt_info *ci;
 
 	if (!!bc != fscrypt_inode_uses_inline_crypto(inode))
 		return false;
 	if (!bc)
 		return true;
 
+	ci = fscrypt_get_lblk_info(inode, next_lblk, NULL, NULL);
 	/*
 	 * Comparing the key pointers is good enough, as all I/O for each key
 	 * uses the same pointer.  I.e., there's currently no need to support
 	 * merging requests where the keys are the same but the pointers differ.
 	 */
-	if (bc->bc_key != inode->i_crypt_info->ci_enc_key->blk_key)
+	if (bc->bc_key != ci->ci_enc_key->blk_key)
 		return false;
 
-	fscrypt_generate_dun(inode->i_crypt_info, next_lblk, next_dun);
+	fscrypt_generate_dun(ci, next_lblk, next_dun);
 	return bio_crypt_dun_is_contiguous(bc, bio->bi_iter.bi_size, next_dun);
 }
 EXPORT_SYMBOL_GPL(fscrypt_mergeable_bio);
@@ -465,7 +467,7 @@ u64 fscrypt_limit_io_blocks(const struct inode *inode, u64 lblk, u64 nr_blocks)
 	if (nr_blocks <= 1)
 		return nr_blocks;
 
-	ci = inode->i_crypt_info;
+	ci = fscrypt_get_lblk_info(inode, lblk, NULL, NULL);
 	if (!(fscrypt_policy_flags(&ci->ci_policy) &
 	      FSCRYPT_POLICY_FLAG_IV_INO_LBLK_32))
 		return nr_blocks;
-- 
2.41.0