fscrypt: calculate NUL-padding length in one place only

Currently, when encrypting a filename (either a real filename or a
symlink target) we calculate the amount of NUL-padding twice: once
before encryption and once during encryption in fname_encrypt().  It is
needed before encryption to allocate the needed buffer size as well as
calculate the size the symlink target will take up on-disk before
creating the symlink inode.  Calculating the size during encryption as
well is redundant.

Remove this redundancy by always calculating the exact size beforehand,
and making fname_encrypt() just add as much NUL padding as is needed to
fill the output buffer.

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 cae7d1b..65424b8 100644 (file)
--- a/fs/crypto/fname.c
+++ b/fs/crypto/fname.c
@@ -30,39 +30,29 @@ static inline bool fscrypt_is_dot_dotdot(const struct qstr *str)
 /**
  * fname_encrypt() - encrypt a filename
  *
- * The caller must have allocated sufficient memory for the @oname string.
+ * The output buffer must be at least as large as the input buffer.
+ * Any extra space is filled with NUL padding before encryption.
  *
  * Return: 0 on success, -errno on failure
  */
-int fname_encrypt(struct inode *inode,
-                 const struct qstr *iname, struct fscrypt_str *oname)
+int fname_encrypt(struct inode *inode, const struct qstr *iname,
+                 u8 *out, unsigned int olen)
 {
        struct skcipher_request *req = NULL;
        DECLARE_CRYPTO_WAIT(wait);
-       struct fscrypt_info *ci = inode->i_crypt_info;
-       struct crypto_skcipher *tfm = ci->ci_ctfm;
+       struct crypto_skcipher *tfm = inode->i_crypt_info->ci_ctfm;
        int res = 0;
        char iv[FS_CRYPTO_BLOCK_SIZE];
        struct scatterlist sg;
-       int padding = 4 << (ci->ci_flags & FS_POLICY_FLAGS_PAD_MASK);
-       unsigned int lim;
-       unsigned int cryptlen;
-
-       lim = inode->i_sb->s_cop->max_namelen(inode);
-       if (iname->len <= 0 || iname->len > lim)
-               return -EIO;
 
        /*
         * Copy the filename to the output buffer for encrypting in-place and
         * pad it with the needed number of NUL bytes.
         */
-       if (WARN_ON(oname->len < iname->len))
+       if (WARN_ON(olen < iname->len))
                return -ENOBUFS;
-       cryptlen = max_t(unsigned int, iname->len, FS_CRYPTO_BLOCK_SIZE);
-       cryptlen = round_up(cryptlen, padding);
-       cryptlen = min3(cryptlen, lim, oname->len);
-       memcpy(oname->name, iname->name, iname->len);
-       memset(oname->name + iname->len, 0, cryptlen - iname->len);
+       memcpy(out, iname->name, iname->len);
+       memset(out + iname->len, 0, olen - iname->len);
 
        /* Initialize the IV */
        memset(iv, 0, FS_CRYPTO_BLOCK_SIZE);
@@ -77,8 +67,8 @@ int fname_encrypt(struct inode *inode,
        skcipher_request_set_callback(req,
                        CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
                        crypto_req_done, &wait);
-       sg_init_one(&sg, oname->name, cryptlen);
-       skcipher_request_set_crypt(req, &sg, &sg, cryptlen, iv);
+       sg_init_one(&sg, out, olen);
+       skcipher_request_set_crypt(req, &sg, &sg, olen, iv);
 
        /* Do the encryption */
        res = crypto_wait_req(crypto_skcipher_encrypt(req), &wait);
@@ -89,7 +79,6 @@ int fname_encrypt(struct inode *inode,
                return res;
        }
 
-       oname->len = cryptlen;
        return 0;
 }
 
@@ -354,11 +343,21 @@ int fscrypt_setup_filename(struct inode *dir, const struct qstr *iname,
                return ret;
 
        if (dir->i_crypt_info) {
-               ret = fscrypt_fname_alloc_buffer(dir, iname->len,
-                                                       &fname->crypto_buf);
-               if (ret)
-                       return ret;
-               ret = fname_encrypt(dir, iname, &fname->crypto_buf);
+               unsigned int max_len = dir->i_sb->s_cop->max_namelen(dir);
+
+               if (iname->len > max_len)
+                       return -ENAMETOOLONG;
+
+               fname->crypto_buf.len =
+                       min(fscrypt_fname_encrypted_size(dir, iname->len),
+                           max_len);
+               fname->crypto_buf.name = kmalloc(fname->crypto_buf.len,
+                                                GFP_NOFS);
+               if (!fname->crypto_buf.name)
+                       return -ENOMEM;
+
+               ret = fname_encrypt(dir, iname, fname->crypto_buf.name,
+                                   fname->crypto_buf.len);
                if (ret)
                        goto errout;
                fname->disk_name.name = fname->crypto_buf.name;
@@ -410,7 +409,7 @@ int fscrypt_setup_filename(struct inode *dir, const struct qstr *iname,
        return 0;
 
 errout:
-       fscrypt_fname_free_buffer(&fname->crypto_buf);
+       kfree(fname->crypto_buf.name);
        return ret;
 }
 EXPORT_SYMBOL(fscrypt_setup_filename);

diff --git a/fs/crypto/fscrypt_private.h b/fs/crypto/fscrypt_private.h
index cec9ce3..0539175 100644 (file)
--- a/fs/crypto/fscrypt_private.h
+++ b/fs/crypto/fscrypt_private.h
@@ -108,8 +108,8 @@ extern struct page *fscrypt_alloc_bounce_page(struct fscrypt_ctx *ctx,
                                              gfp_t gfp_flags);
 
 /* fname.c */
-extern int fname_encrypt(struct inode *inode,
-                        const struct qstr *iname, struct fscrypt_str *oname);
+extern int fname_encrypt(struct inode *inode, const struct qstr *iname,
+                        u8 *out, unsigned int olen);
 
 /* keyinfo.c */
 extern void __exit fscrypt_essiv_cleanup(void);

diff --git a/fs/crypto/hooks.c b/fs/crypto/hooks.c
index 8900e34..5bf38d9 100644 (file)
--- a/fs/crypto/hooks.c
+++ b/fs/crypto/hooks.c
@@ -161,7 +161,6 @@ int __fscrypt_encrypt_symlink(struct inode *inode, const char *target,
        struct qstr iname = { .name = target, .len = len };
        struct fscrypt_symlink_data *sd;
        unsigned int ciphertext_len;
-       struct fscrypt_str oname;
 
        err = fscrypt_require_key(inode);
        if (err)
@@ -178,16 +177,12 @@ int __fscrypt_encrypt_symlink(struct inode *inode, const char *target,
        ciphertext_len = disk_link->len - sizeof(*sd);
        sd->len = cpu_to_le16(ciphertext_len);
 
-       oname.name = sd->encrypted_path;
-       oname.len = ciphertext_len;
-       err = fname_encrypt(inode, &iname, &oname);
+       err = fname_encrypt(inode, &iname, sd->encrypted_path, ciphertext_len);
        if (err) {
                if (!disk_link->name)
                        kfree(sd);
                return err;
        }
-       BUG_ON(oname.len != ciphertext_len);
-
        /*
         * Null-terminating the ciphertext doesn't make sense, but we still
         * count the null terminator in the length, so we might as well