fscrypt: Cleanup fscrypt_{decrypt,encrypt}_page()

- Improve documentation
- Add BUG_ON(len == 0) to avoid accidental switch of offs and len
parameters
- Improve variable names for readability

Signed-off-by: David Gstir <david@sigma-star.at>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

1 files changed, 52 insertions, 41 deletions

diff --git a/fs/crypto/crypto.c b/fs/crypto/crypto.c
index f287f76cc906..8c104e712bb2 100644
--- a/fs/crypto/crypto.c
+++ b/fs/crypto/crypto.c
@@ -147,9 +147,9 @@ typedef enum {
 } fscrypt_direction_t;
 
 static int do_page_crypto(const struct inode *inode,
-                        fscrypt_direction_t rw, pgoff_t index,
+                        fscrypt_direction_t rw, u64 lblk_num,
                         struct page *src_page, struct page *dest_page,
-                        unsigned int src_len, unsigned int src_offset,
+                        unsigned int len, unsigned int offs,
                         gfp_t gfp_flags)
 {
         struct {
@@ -163,6 +163,8 @@ static int do_page_crypto(const struct inode *inode,
         struct crypto_skcipher *tfm = ci->ci_ctfm;
         int res = 0;
 
+        BUG_ON(len == 0);
+
         req = skcipher_request_alloc(tfm, gfp_flags);
         if (!req) {
                 printk_ratelimited(KERN_ERR
@@ -176,14 +178,14 @@ static int do_page_crypto(const struct inode *inode,
                 page_crypt_complete, &ecr);
 
         BUILD_BUG_ON(sizeof(xts_tweak) != FS_XTS_TWEAK_SIZE);
-        xts_tweak.index = cpu_to_le64(index);
+        xts_tweak.index = cpu_to_le64(lblk_num);
         memset(xts_tweak.padding, 0, sizeof(xts_tweak.padding));
 
         sg_init_table(&dst, 1);
-        sg_set_page(&dst, dest_page, src_len, src_offset);
+        sg_set_page(&dst, dest_page, len, offs);
         sg_init_table(&src, 1);
-        sg_set_page(&src, src_page, src_len, src_offset);
-        skcipher_request_set_crypt(req, &src, &dst, src_len, &xts_tweak);
+        sg_set_page(&src, src_page, len, offs);
+        skcipher_request_set_crypt(req, &src, &dst, len, &xts_tweak);
         if (rw == FS_DECRYPT)
                 res = crypto_skcipher_decrypt(req);
         else
@@ -214,44 +216,53 @@ static struct page *alloc_bounce_page(struct fscrypt_ctx *ctx, gfp_t gfp_flags)
 
 /**
  * fscypt_encrypt_page() - Encrypts a page
- * @inode:            The inode for which the encryption should take place
- * @plaintext_page:   The page to encrypt. Must be locked.
- * @plaintext_len:    Length of plaintext within page
- * @plaintext_offset: Offset of plaintext within page
- * @index:            Index for encryption. This is mainly the page index, but
- *                    but might be different for multiple calls on same page.
- * @gfp_flags:        The gfp flag for memory allocation
+ * @inode:     The inode for which the encryption should take place
+ * @page:      The page to encrypt. Must be locked for bounce-page
+ *             encryption.
+ * @len:       Length of data to encrypt in @page and encrypted
+ *             data in returned page.
+ * @offs:      Offset of data within @page and returned
+ *             page holding encrypted data.
+ * @lblk_num:  Logical block number. This must be unique for multiple
+ *             calls with same inode, except when overwriting
+ *             previously written data.
+ * @gfp_flags: The gfp flag for memory allocation
  *
- * Encrypts plaintext_page using the ctx encryption context. If
- * the filesystem supports it, encryption is performed in-place, otherwise a
- * new ciphertext_page is allocated and returned.
+ * Encrypts @page using the ctx encryption context. Performs encryption
+ * either in-place or into a newly allocated bounce page.
+ * Called on the page write path.
  *
- * Called on the page write path.  The caller must call
+ * Bounce page allocation is the default.
+ * In this case, the contents of @page are encrypted and stored in an
+ * allocated bounce page. @page has to be locked and the caller must call
  * fscrypt_restore_control_page() on the returned ciphertext page to
  * release the bounce buffer and the encryption context.
  *
- * Return: An allocated page with the encrypted content on success. Else, an
+ * In-place encryption is used by setting the FS_CFLG_INPLACE_ENCRYPTION flag in
+ * fscrypt_operations. Here, the input-page is returned with its content
+ * encrypted.
+ *
+ * Return: A page with the encrypted content on success. Else, an
  * error value or NULL.
  */
 struct page *fscrypt_encrypt_page(const struct inode *inode,
-                                struct page *plaintext_page,
-                                unsigned int plaintext_len,
-                                unsigned int plaintext_offset,
-                                pgoff_t index, gfp_t gfp_flags)
+                                struct page *page,
+                                unsigned int len,
+                                unsigned int offs,
+                                u64 lblk_num, gfp_t gfp_flags)
 
 {
         struct fscrypt_ctx *ctx;
-        struct page *ciphertext_page = plaintext_page;
+        struct page *ciphertext_page = page;
         int err;
 
-        BUG_ON(plaintext_len % FS_CRYPTO_BLOCK_SIZE != 0);
+        BUG_ON(len % FS_CRYPTO_BLOCK_SIZE != 0);
 
         if (inode->i_sb->s_cop->flags & FS_CFLG_INPLACE_ENCRYPTION) {
                 /* with inplace-encryption we just encrypt the page */
-                err = do_page_crypto(inode, FS_ENCRYPT, index,
-                                        plaintext_page, ciphertext_page,
-                                        plaintext_len, plaintext_offset,
-                                        gfp_flags);
+                err = do_page_crypto(inode, FS_ENCRYPT, lblk_num,
+                                        page, ciphertext_page,
+                                        len, offs, gfp_flags);
                 if (err)
                         return ERR_PTR(err);
 
@@ -267,11 +278,10 @@ struct page *fscrypt_encrypt_page(const struct inode *inode,
         if (IS_ERR(ciphertext_page))
                 goto errout;
 
-        ctx->w.control_page = plaintext_page;
-        err = do_page_crypto(inode, FS_ENCRYPT, index,
-                                        plaintext_page, ciphertext_page,
-                                        plaintext_len, plaintext_offset,
-                                        gfp_flags);
+        ctx->w.control_page = page;
+        err = do_page_crypto(inode, FS_ENCRYPT, lblk_num,
+                                        page, ciphertext_page,
+                                        len, offs, gfp_flags);
         if (err) {
                 ciphertext_page = ERR_PTR(err);
                 goto errout;
@@ -289,11 +299,12 @@ EXPORT_SYMBOL(fscrypt_encrypt_page);
 
 /**
  * fscrypt_decrypt_page() - Decrypts a page in-place
- * @inode: Encrypted inode to decrypt.
- * @page:  The page to decrypt. Must be locked.
- * @len:   Number of bytes in @page to be decrypted.
- * @offs:  Start of data in @page.
- * @index: Index for encryption.
+ * @inode:     The corresponding inode for the page to decrypt.
+ * @page:      The page to decrypt. Must be locked in case
+ *             it is a writeback page.
+ * @len:       Number of bytes in @page to be decrypted.
+ * @offs:      Start of data in @page.
+ * @lblk_num:  Logical block number.
  *
  * Decrypts page in-place using the ctx encryption context.
  *
@@ -302,10 +313,10 @@ EXPORT_SYMBOL(fscrypt_encrypt_page);
  * Return: Zero on success, non-zero otherwise.
  */
 int fscrypt_decrypt_page(const struct inode *inode, struct page *page,
-                        unsigned int len, unsigned int offs, pgoff_t index)
+                        unsigned int len, unsigned int offs, u64 lblk_num)
 {
-        return do_page_crypto(inode, FS_DECRYPT, index, page, page, len, offs,
-                        GFP_NOFS);
+        return do_page_crypto(inode, FS_DECRYPT, lblk_num, page, page, len,
+                        offs, GFP_NOFS);
 }
 EXPORT_SYMBOL(fscrypt_decrypt_page);