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Date: Thu, 15 Sep 2016 03:50:47 -0600
From: Andreas Dilger <adilger@...ger.ca>
To: Eric Biggers <ebiggers@...gle.com>
Cc: linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org,
linux-f2fs-devel@...ts.sourceforge.net, tytso@....edu,
jaegeuk@...nel.org
Subject: Re: [PATCH] fscrypto: make filename crypto functions return 0 on success
On Sep 14, 2016, at 5:00 PM, Eric Biggers <ebiggers@...gle.com> 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'.
>
> 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@...gle.com>
Reviewed-by: Andreas Dilger <adilger@...ger.ca>
> ---
> 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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Cheers, Andreas
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