Commit 3b0d8837 authored by Eric Biggers's avatar Eric Biggers Committed by Theodore Ts'o
Browse files

fscrypt: new helper function - fscrypt_get_symlink() 



Filesystems also have duplicate code to support ->get_link() on
encrypted symlinks.  Factor it out into a new function
fscrypt_get_symlink().  It takes in the contents of the encrypted
symlink on-disk and provides the target (decrypted or encoded) that
should be returned from ->get_link().

Signed-off-by: default avatarEric Biggers <ebiggers@google.com>
Signed-off-by: default avatarTheodore Ts'o <tytso@mit.edu>
parent 76e81d6d

fs/crypto/hooks.c

+73 −0
Original line number Diff line number Diff line
@@ -200,3 +200,76 @@ int __fscrypt_encrypt_symlink(struct inode *inode, const char *target, 
	return 0;

}

EXPORT_SYMBOL_GPL(__fscrypt_encrypt_symlink);



/**

 * fscrypt_get_symlink - get the target of an encrypted symlink

 * @inode: the symlink inode

 * @caddr: the on-disk contents of the symlink

 * @max_size: size of @caddr buffer

 * @done: if successful, will be set up to free the returned target

 *

 * If the symlink's encryption key is available, we decrypt its target.

 * Otherwise, we encode its target for presentation.

 *

 * This may sleep, so the filesystem must have dropped out of RCU mode already.

 *

 * Return: the presentable symlink target or an ERR_PTR()

 */

const char *fscrypt_get_symlink(struct inode *inode, const void *caddr,

				unsigned int max_size,

				struct delayed_call *done)

{

	const struct fscrypt_symlink_data *sd;

	struct fscrypt_str cstr, pstr;

	int err;



	/* This is for encrypted symlinks only */

	if (WARN_ON(!IS_ENCRYPTED(inode)))

		return ERR_PTR(-EINVAL);



	/*

	 * Try to set up the symlink's encryption key, but we can continue

	 * regardless of whether the key is available or not.

	 */

	err = fscrypt_get_encryption_info(inode);

	if (err)

		return ERR_PTR(err);



	/*

	 * For historical reasons, encrypted symlink targets are prefixed with

	 * the ciphertext length, even though this is redundant with i_size.

	 */



	if (max_size < sizeof(*sd))

		return ERR_PTR(-EUCLEAN);

	sd = caddr;

	cstr.name = (unsigned char *)sd->encrypted_path;

	cstr.len = le16_to_cpu(sd->len);



	if (cstr.len == 0)

		return ERR_PTR(-EUCLEAN);



	if (cstr.len + sizeof(*sd) - 1 > max_size)

		return ERR_PTR(-EUCLEAN);



	err = fscrypt_fname_alloc_buffer(inode, cstr.len, &pstr);

	if (err)

		return ERR_PTR(err);



	err = fscrypt_fname_disk_to_usr(inode, 0, 0, &cstr, &pstr);

	if (err)

		goto err_kfree;



	err = -EUCLEAN;

	if (pstr.name[0] == '\0')

		goto err_kfree;



	pstr.name[pstr.len] = '\0';

	set_delayed_call(done, kfree_link, pstr.name);

	return pstr.name;



err_kfree:

	kfree(pstr.name);

	return ERR_PTR(err);

}

EXPORT_SYMBOL_GPL(fscrypt_get_symlink);

include/linux/fscrypt_notsupp.h

+8 −0
Original line number Diff line number Diff line
@@ -239,4 +239,12 @@ static inline int __fscrypt_encrypt_symlink(struct inode *inode, 
	return -EOPNOTSUPP;

}



static inline const char *fscrypt_get_symlink(struct inode *inode,

					      const void *caddr,

					      unsigned int max_size,

					      struct delayed_call *done)

{

	return ERR_PTR(-EOPNOTSUPP);

}



#endif	/* _LINUX_FSCRYPT_NOTSUPP_H */

include/linux/fscrypt_supp.h

+3 −0
Original line number Diff line number Diff line
@@ -211,5 +211,8 @@ extern int __fscrypt_prepare_symlink(struct inode *dir, unsigned int len, 
extern int __fscrypt_encrypt_symlink(struct inode *inode, const char *target,

				     unsigned int len,

				     struct fscrypt_str *disk_link);

extern const char *fscrypt_get_symlink(struct inode *inode, const void *caddr,

				       unsigned int max_size,

				       struct delayed_call *done);



#endif	/* _LINUX_FSCRYPT_SUPP_H */

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