fscrypt: define fscrypt_fname_alloc_buffer() to be for presented names

Previously fscrypt_fname_alloc_buffer() was used to allocate buffers for
both presented (decrypted or encoded) and encrypted filenames.  That was
confusing, because it had to allocate the worst-case size for either,
e.g. including NUL-padding even when it was meaningless.

But now that fscrypt_setup_filename() no longer calls it, it is only
used in the ->get_link() and ->readdir() paths, which specifically want
a buffer for presented filenames.  Therefore, switch the behavior over
to allocating the buffer for presented filenames only.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

diff --git a/fs/crypto/fname.c b/fs/crypto/fname.c
index 65424b8..44ddd09 100644 (file)
--- a/fs/crypto/fname.c
+++ b/fs/crypto/fname.c
@@ -204,37 +204,36 @@ u32 fscrypt_fname_encrypted_size(const struct inode *inode, u32 ilen)
 EXPORT_SYMBOL(fscrypt_fname_encrypted_size);
 
 /**
- * fscrypt_fname_crypto_alloc_obuff() -
+ * fscrypt_fname_alloc_buffer - allocate a buffer for presented filenames
  *
- * Allocates an output buffer that is sufficient for the crypto operation
- * specified by the context and the direction.
+ * Allocate a buffer that is large enough to hold any decrypted or encoded
+ * filename (null-terminated), for the given maximum encrypted filename length.
+ *
+ * Return: 0 on success, -errno on failure
  */
 int fscrypt_fname_alloc_buffer(const struct inode *inode,
-                               u32 ilen, struct fscrypt_str *crypto_str)
+                              u32 max_encrypted_len,
+                              struct fscrypt_str *crypto_str)
 {
-       u32 olen = fscrypt_fname_encrypted_size(inode, ilen);
        const u32 max_encoded_len =
                max_t(u32, BASE64_CHARS(FSCRYPT_FNAME_MAX_UNDIGESTED_SIZE),
                      1 + BASE64_CHARS(sizeof(struct fscrypt_digested_name)));
+       u32 max_presented_len;
 
-       crypto_str->len = olen;
-       olen = max(olen, max_encoded_len);
+       max_presented_len = max(max_encoded_len, max_encrypted_len);
 
-       /*
-        * Allocated buffer can hold one more character to null-terminate the
-        * string
-        */
-       crypto_str->name = kmalloc(olen + 1, GFP_NOFS);
-       if (!(crypto_str->name))
+       crypto_str->name = kmalloc(max_presented_len + 1, GFP_NOFS);
+       if (!crypto_str->name)
                return -ENOMEM;
+       crypto_str->len = max_presented_len;
        return 0;
 }
 EXPORT_SYMBOL(fscrypt_fname_alloc_buffer);
 
 /**
- * fscrypt_fname_crypto_free_buffer() -
+ * fscrypt_fname_free_buffer - free the buffer for presented filenames
  *
- * Frees the buffer allocated for crypto operation.
+ * Free the buffer allocated by fscrypt_fname_alloc_buffer().
  */
 void fscrypt_fname_free_buffer(struct fscrypt_str *crypto_str)
 {

diff --git a/include/linux/fscrypt_notsupp.h b/include/linux/fscrypt_notsupp.h
index 0962f50..c9592e3 100644 (file)
--- a/include/linux/fscrypt_notsupp.h
+++ b/include/linux/fscrypt_notsupp.h
@@ -140,7 +140,7 @@ static inline u32 fscrypt_fname_encrypted_size(const struct inode *inode,
 }
 
 static inline int fscrypt_fname_alloc_buffer(const struct inode *inode,
-                                            u32 ilen,
+                                            u32 max_encrypted_len,
                                             struct fscrypt_str *crypto_str)
 {
        return -EOPNOTSUPP;