fscrypt: cache decrypted symlink target in ->i_link

Message ID	20190409233544.156665-1-ebiggers@kernel.org
State	Not Applicable
Headers	show Return-Path: <linux-ext4-owner@vger.kernel.org> From: Eric Biggers <ebiggers@kernel.org> To: linux-fscrypt@vger.kernel.org Cc: linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net Subject: [PATCH] fscrypt: cache decrypted symlink target in ->i_link Date: Tue, 9 Apr 2019 16:35:44 -0700 Message-Id: <20190409233544.156665-1-ebiggers@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-ext4-owner@vger.kernel.org Precedence: bulk
Series	fscrypt: cache decrypted symlink target in ->i_link \| expand fscrypt: cache decrypted symlink target in ->i_link

diff --git a/fs/crypto/hooks.c b/fs/crypto/hooks.c index 56debb1fcf5eb..e6b09de51221f 100644 --- a/fs/crypto/hooks.c +++ b/fs/crypto/hooks.c @@ -179,11 +179,9 @@ int __fscrypt_encrypt_symlink(struct inode *inode, const char *target, sd->len = cpu_to_le16(ciphertext_len); err = fname_encrypt(inode, &iname, sd->encrypted_path, ciphertext_len); - if (err) { - if (!disk_link->name) - kfree(sd); - return err; - } + if (err) + goto err_free_sd; + /* * Null-terminating the ciphertext doesn't make sense, but we still * count the null terminator in the length, so we might as well @@ -191,9 +189,20 @@ int __fscrypt_encrypt_symlink(struct inode *inode, const char *target, */ sd->encrypted_path[ciphertext_len] = '\0'; + /* Cache the plaintext symlink target for later use by ->get_link(). */ + err = -ENOMEM; + inode->i_link = kmemdup(target, len + 1, GFP_NOFS); + if (!inode->i_link) + goto err_free_sd; + if (!disk_link->name) disk_link->name = (unsigned char *)sd; return 0; + +err_free_sd: + if (!disk_link->name) + kfree(sd); + return err; } EXPORT_SYMBOL_GPL(__fscrypt_encrypt_symlink); @@ -202,7 +211,7 @@ EXPORT_SYMBOL_GPL(__fscrypt_encrypt_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 + * @done: if successful, will be set up to free the returned target if needed * * If the symlink's encryption key is available, we decrypt its target. * Otherwise, we encode its target for presentation. @@ -217,12 +226,18 @@ const char *fscrypt_get_symlink(struct inode *inode, const void *caddr, { const struct fscrypt_symlink_data *sd; struct fscrypt_str cstr, pstr; + bool has_key; int err; /* This is for encrypted symlinks only */ if (WARN_ON(!IS_ENCRYPTED(inode))) return ERR_PTR(-EINVAL); + /* If the decrypted target is already cached, just return it. */ + pstr.name = (char *)fscrypt_get_cached_symlink(inode); + if (pstr.name) + return pstr.name; + /* * Try to set up the symlink's encryption key, but we can continue * regardless of whether the key is available or not. @@ -230,6 +245,7 @@ const char *fscrypt_get_symlink(struct inode *inode, const void *caddr, err = fscrypt_get_encryption_info(inode); if (err) return ERR_PTR(err); + has_key = fscrypt_has_encryption_key(inode); /* * For historical reasons, encrypted symlink targets are prefixed with @@ -261,7 +277,16 @@ const char *fscrypt_get_symlink(struct inode *inode, const void *caddr, goto err_kfree; pstr.name[pstr.len] = '\0'; - set_delayed_call(done, kfree_link, pstr.name); + + /* + * Cache decrypted symlink targets in i_link for later use. Don't cache + * symlink targets encoded without the key, since those become outdated + * once the key is added. This pairs with fscrypt_get_cached_symlink(). + */ + if (!has_key || + cmpxchg_release(&inode->i_link, NULL, pstr.name) != NULL) + set_delayed_call(done, kfree_link, pstr.name); + return pstr.name; err_kfree: diff --git a/fs/crypto/keyinfo.c b/fs/crypto/keyinfo.c index d1f0f8369d510..bf9b0bffd81bc 100644 --- a/fs/crypto/keyinfo.c +++ b/fs/crypto/keyinfo.c @@ -586,6 +586,10 @@ EXPORT_SYMBOL(fscrypt_get_encryption_info); void fscrypt_put_encryption_info(struct inode *inode) { + if (IS_ENCRYPTED(inode) && S_ISLNK(inode->i_mode)) { + kfree(inode->i_link); + inode->i_link = NULL; + } put_crypt_info(inode->i_crypt_info); inode->i_crypt_info = NULL; } diff --git a/fs/ext4/symlink.c b/fs/ext4/symlink.c index dd05af983092d..02b49ef4762fd 100644 --- a/fs/ext4/symlink.c +++ b/fs/ext4/symlink.c @@ -35,6 +35,10 @@ static const char *ext4_encrypted_get_link(struct dentry *dentry, if (!dentry) return ERR_PTR(-ECHILD); + paddr = fscrypt_get_cached_symlink(inode); + if (paddr) + return paddr; + if (ext4_inode_is_fast_symlink(inode)) { caddr = EXT4_I(inode)->i_data; max_size = sizeof(EXT4_I(inode)->i_data); diff --git a/fs/f2fs/namei.c b/fs/f2fs/namei.c index f5e34e4670031..2f38df6e26f80 100644 --- a/fs/f2fs/namei.c +++ b/fs/f2fs/namei.c @@ -1212,6 +1212,10 @@ static const char *f2fs_encrypted_get_link(struct dentry *dentry, if (!dentry) return ERR_PTR(-ECHILD); + target = fscrypt_get_cached_symlink(inode); + if (target) + return target; + page = read_mapping_page(inode->i_mapping, 0, NULL); if (IS_ERR(page)) return ERR_CAST(page); diff --git a/include/linux/fscrypt.h b/include/linux/fscrypt.h index 13c907214a761..f4b816c5a0941 100644 --- a/include/linux/fscrypt.h +++ b/include/linux/fscrypt.h @@ -231,6 +231,24 @@ extern int __fscrypt_encrypt_symlink(struct inode *inode, const char *target, extern const char *fscrypt_get_symlink(struct inode *inode, const void *caddr, unsigned int max_size, struct delayed_call *done); +/** + * fscrypt_get_cached_symlink - get the cached decrypted symlink target + * @inode: inode of an encrypted symlink + * + * If the decrypted symlink target was already cached, return it. + * + * This must not be called in RCU-walk mode, since currently the cached symlink + * target is freed without waiting for an RCU grace period. + * + * Return: the symlink target if cached; NULL if uncached; + * or ERR_PTR(-EOPNOTSUPP) when !CONFIG_FS_ENCRYPTION. + */ +static inline const char *fscrypt_get_cached_symlink(const struct inode *inode) +{ + /* Pairs with the cmpxchg_release() in fscrypt_get_symlink() */ + return smp_load_acquire(&inode->i_link); +} + #else /* !CONFIG_FS_ENCRYPTION */ static inline bool fscrypt_has_encryption_key(const struct inode *inode) @@ -446,6 +464,11 @@ static inline const char *fscrypt_get_symlink(struct inode *inode, { return ERR_PTR(-EOPNOTSUPP); } + +static inline const char *fscrypt_get_cached_symlink(const struct inode *inode) +{ + return ERR_PTR(-EOPNOTSUPP); +} #endif /* !CONFIG_FS_ENCRYPTION */ /**

fscrypt: cache decrypted symlink target in ->i_link

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