Re: [PATCH] fscrypto: make filename crypto functions return 0 on success

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Hi Eric,

On Wed, Sep 14, 2016 at 04:00:45PM -0700, Eric Biggers wrote:
> Several filename crypto functions: fname_decrypt(),
> fscrypt_fname_disk_to_usr(), and fscrypt_fname_usr_to_disk(), returned
> the output length on success or -errno on failure.  However, the output
> length was redundant with the value written to 'oname->len'.  It is also
> potentially error-prone to make callers have to check for '< 0' instead
> of '!= 0'.

At a glance, you missed some places like
- fscrypt_fname_usr_to_disk() in ext4_symlink() and f2fs_symlink()
- fscrypt_fname_disk_to_usr() in dx_show_leaf() and f2fs_fill_dentries()

Thanks,

> Therefore, make these functions return 0 instead of a length, and make
> the callers who cared about the return value being a length use
> 'oname->len' instead.
> 
> This change also fixes the inconsistency of fname_encrypt() actually
> already returning 0 on success, not a length like the other filename
> crypto functions and as documented in its function comment.
> 
> Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx>
> ---
>  fs/crypto/fname.c | 52 ++++++++++++++++++++++++++++++----------------------
>  fs/ext4/dir.c     |  5 +++--
>  fs/ext4/symlink.c |  5 ++---
>  fs/f2fs/namei.c   |  4 ++--
>  4 files changed, 37 insertions(+), 29 deletions(-)
> 
> diff --git a/fs/crypto/fname.c b/fs/crypto/fname.c
> index 6bbc3b1..49fd564 100644
> --- a/fs/crypto/fname.c
> +++ b/fs/crypto/fname.c
> @@ -35,11 +35,11 @@ static void fname_crypt_complete(struct crypto_async_request *req, int res)
>  }
>  
>  /**
> - * fname_encrypt() -
> + * fname_encrypt() - encrypt a filename
>   *
> - * This function encrypts the input filename, and returns the length of the
> - * ciphertext. Errors are returned as negative numbers.  We trust the caller to
> - * allocate sufficient memory to oname string.
> + * The caller must have allocated sufficient memory for the @oname string.
> + *
> + * Return: 0 on success, -errno on failure
>   */
>  static int fname_encrypt(struct inode *inode,
>  			const struct qstr *iname, struct fscrypt_str *oname)
> @@ -105,20 +105,22 @@ static int fname_encrypt(struct inode *inode,
>  	}
>  	kfree(alloc_buf);
>  	skcipher_request_free(req);
> -	if (res < 0)
> +	if (res < 0) {
>  		printk_ratelimited(KERN_ERR
>  				"%s: Error (error code %d)\n", __func__, res);
> +		return res;
> +	}
>  
>  	oname->len = ciphertext_len;
> -	return res;
> +	return 0;
>  }
>  
> -/*
> - * fname_decrypt()
> - *	This function decrypts the input filename, and returns
> - *	the length of the plaintext.
> - *	Errors are returned as negative numbers.
> - *	We trust the caller to allocate sufficient memory to oname string.
> +/**
> + * fname_decrypt() - decrypt a filename
> + *
> + * The caller must have allocated sufficient memory for the @oname string.
> + *
> + * Return: 0 on success, -errno on failure
>   */
>  static int fname_decrypt(struct inode *inode,
>  				const struct fscrypt_str *iname,
> @@ -168,7 +170,7 @@ static int fname_decrypt(struct inode *inode,
>  	}
>  
>  	oname->len = strnlen(oname->name, iname->len);
> -	return oname->len;
> +	return 0;
>  }
>  
>  static const char *lookup_table =
> @@ -279,6 +281,10 @@ EXPORT_SYMBOL(fscrypt_fname_free_buffer);
>  /**
>   * fscrypt_fname_disk_to_usr() - converts a filename from disk space to user
>   * space
> + *
> + * The caller must have allocated sufficient memory for the @oname string.
> + *
> + * Return: 0 on success, -errno on failure
>   */
>  int fscrypt_fname_disk_to_usr(struct inode *inode,
>  			u32 hash, u32 minor_hash,
> @@ -287,13 +293,12 @@ int fscrypt_fname_disk_to_usr(struct inode *inode,
>  {
>  	const struct qstr qname = FSTR_TO_QSTR(iname);
>  	char buf[24];
> -	int ret;
>  
>  	if (fscrypt_is_dot_dotdot(&qname)) {
>  		oname->name[0] = '.';
>  		oname->name[iname->len - 1] = '.';
>  		oname->len = iname->len;
> -		return oname->len;
> +		return 0;
>  	}
>  
>  	if (iname->len < FS_CRYPTO_BLOCK_SIZE)
> @@ -303,9 +308,9 @@ int fscrypt_fname_disk_to_usr(struct inode *inode,
>  		return fname_decrypt(inode, iname, oname);
>  
>  	if (iname->len <= FS_FNAME_CRYPTO_DIGEST_SIZE) {
> -		ret = digest_encode(iname->name, iname->len, oname->name);
> -		oname->len = ret;
> -		return ret;
> +		oname->len = digest_encode(iname->name, iname->len,
> +					   oname->name);
> +		return 0;
>  	}
>  	if (hash) {
>  		memcpy(buf, &hash, 4);
> @@ -315,15 +320,18 @@ int fscrypt_fname_disk_to_usr(struct inode *inode,
>  	}
>  	memcpy(buf + 8, iname->name + iname->len - 16, 16);
>  	oname->name[0] = '_';
> -	ret = digest_encode(buf, 24, oname->name + 1);
> -	oname->len = ret + 1;
> -	return ret + 1;
> +	oname->len = 1 + digest_encode(buf, 24, oname->name + 1);
> +	return 0;
>  }
>  EXPORT_SYMBOL(fscrypt_fname_disk_to_usr);
>  
>  /**
>   * fscrypt_fname_usr_to_disk() - converts a filename from user space to disk
>   * space
> + *
> + * The caller must have allocated sufficient memory for the @oname string.
> + *
> + * Return: 0 on success, -errno on failure
>   */
>  int fscrypt_fname_usr_to_disk(struct inode *inode,
>  			const struct qstr *iname,
> @@ -333,7 +341,7 @@ int fscrypt_fname_usr_to_disk(struct inode *inode,
>  		oname->name[0] = '.';
>  		oname->name[iname->len - 1] = '.';
>  		oname->len = iname->len;
> -		return oname->len;
> +		return 0;
>  	}
>  	if (inode->i_crypt_info)
>  		return fname_encrypt(inode, iname, oname);
> diff --git a/fs/ext4/dir.c b/fs/ext4/dir.c
> index 67415e0..4d4b910 100644
> --- a/fs/ext4/dir.c
> +++ b/fs/ext4/dir.c
> @@ -260,11 +260,12 @@ static int ext4_readdir(struct file *file, struct dir_context *ctx)
>  					/* Directory is encrypted */
>  					err = fscrypt_fname_disk_to_usr(inode,
>  						0, 0, &de_name, &fstr);
> +					de_name = fstr;
>  					fstr.len = save_len;
> -					if (err < 0)
> +					if (err)
>  						goto errout;
>  					if (!dir_emit(ctx,
> -					    fstr.name, err,
> +					    de_name.name, de_name.len,
>  					    le32_to_cpu(de->inode),
>  					    get_dtype(sb, de->file_type)))
>  						goto done;
> diff --git a/fs/ext4/symlink.c b/fs/ext4/symlink.c
> index 4d83d9e..55aaf30 100644
> --- a/fs/ext4/symlink.c
> +++ b/fs/ext4/symlink.c
> @@ -67,14 +67,13 @@ static const char *ext4_encrypted_get_link(struct dentry *dentry,
>  		goto errout;
>  
>  	res = fscrypt_fname_disk_to_usr(inode, 0, 0, &cstr, &pstr);
> -	if (res < 0)
> +	if (res)
>  		goto errout;
>  
>  	paddr = pstr.name;
>  
>  	/* Null-terminate the name */
> -	if (res <= pstr.len)
> -		paddr[res] = '\0';
> +	paddr[pstr.len] = '\0';
>  	if (cpage)
>  		put_page(cpage);
>  	set_delayed_call(done, kfree_link, paddr);
> diff --git a/fs/f2fs/namei.c b/fs/f2fs/namei.c
> index 73fa356..a5468c2 100644
> --- a/fs/f2fs/namei.c
> +++ b/fs/f2fs/namei.c
> @@ -1048,7 +1048,7 @@ static const char *f2fs_encrypted_get_link(struct dentry *dentry,
>  		goto errout;
>  
>  	res = fscrypt_fname_disk_to_usr(inode, 0, 0, &cstr, &pstr);
> -	if (res < 0)
> +	if (res)
>  		goto errout;
>  
>  	/* this is broken symlink case */
> @@ -1060,7 +1060,7 @@ static const char *f2fs_encrypted_get_link(struct dentry *dentry,
>  	paddr = pstr.name;
>  
>  	/* Null-terminate the name */
> -	paddr[res] = '\0';
> +	paddr[pstr.len] = '\0';
>  
>  	put_page(cpage);
>  	set_delayed_call(done, kfree_link, paddr);
> -- 
> 2.8.0.rc3.226.g39d4020
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