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fscrypt: cache decrypted symlink target in ->i_link
Path lookups that traverse encrypted symlink(s) are very slow because each encrypted symlink needs to be decrypted each time it's followed. This also involves dropping out of rcu-walk mode. Make encrypted symlinks faster by caching the decrypted symlink target in ->i_link. The first call to fscrypt_get_symlink() sets it. Then, the existing VFS path lookup code uses the non-NULL ->i_link to take the fast path where ->get_link() isn't called, and lookups in rcu-walk mode remain in rcu-walk mode. Also set ->i_link immediately when a new encrypted symlink is created. To safely free the symlink target after an RCU grace period has elapsed, introduce a new function fscrypt_free_inode(), and make the relevant filesystems call it just before actually freeing the inode. Cc: Al Viro <viro@zeniv.linux.org.uk> Signed-off-by: Eric Biggers <ebiggers@google.com> Signed-off-by: Theodore Ts'o <tytso@mit.edu>
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4c4f7c19b3
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2c58d548f5
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@ -189,11 +189,9 @@ int __fscrypt_encrypt_symlink(struct inode *inode, const char *target,
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sd->len = cpu_to_le16(ciphertext_len);
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err = fname_encrypt(inode, &iname, sd->encrypted_path, ciphertext_len);
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if (err) {
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if (!disk_link->name)
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kfree(sd);
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return err;
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}
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if (err)
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goto err_free_sd;
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/*
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* Null-terminating the ciphertext doesn't make sense, but we still
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* count the null terminator in the length, so we might as well
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@ -201,9 +199,20 @@ int __fscrypt_encrypt_symlink(struct inode *inode, const char *target,
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*/
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sd->encrypted_path[ciphertext_len] = '\0';
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/* Cache the plaintext symlink target for later use by get_link() */
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err = -ENOMEM;
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inode->i_link = kmemdup(target, len + 1, GFP_NOFS);
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if (!inode->i_link)
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goto err_free_sd;
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if (!disk_link->name)
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disk_link->name = (unsigned char *)sd;
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return 0;
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err_free_sd:
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if (!disk_link->name)
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kfree(sd);
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return err;
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}
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EXPORT_SYMBOL_GPL(__fscrypt_encrypt_symlink);
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@ -212,7 +221,7 @@ EXPORT_SYMBOL_GPL(__fscrypt_encrypt_symlink);
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* @inode: the symlink inode
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* @caddr: the on-disk contents of the symlink
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* @max_size: size of @caddr buffer
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* @done: if successful, will be set up to free the returned target
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* @done: if successful, will be set up to free the returned target if needed
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*
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* If the symlink's encryption key is available, we decrypt its target.
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* Otherwise, we encode its target for presentation.
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@ -227,12 +236,18 @@ const char *fscrypt_get_symlink(struct inode *inode, const void *caddr,
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{
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const struct fscrypt_symlink_data *sd;
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struct fscrypt_str cstr, pstr;
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bool has_key;
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int err;
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/* This is for encrypted symlinks only */
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if (WARN_ON(!IS_ENCRYPTED(inode)))
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return ERR_PTR(-EINVAL);
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/* If the decrypted target is already cached, just return it. */
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pstr.name = READ_ONCE(inode->i_link);
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if (pstr.name)
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return pstr.name;
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/*
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* Try to set up the symlink's encryption key, but we can continue
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* regardless of whether the key is available or not.
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@ -240,6 +255,7 @@ const char *fscrypt_get_symlink(struct inode *inode, const void *caddr,
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err = fscrypt_get_encryption_info(inode);
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if (err)
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return ERR_PTR(err);
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has_key = fscrypt_has_encryption_key(inode);
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/*
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* For historical reasons, encrypted symlink targets are prefixed with
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@ -271,7 +287,17 @@ const char *fscrypt_get_symlink(struct inode *inode, const void *caddr,
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goto err_kfree;
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pstr.name[pstr.len] = '\0';
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set_delayed_call(done, kfree_link, pstr.name);
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/*
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* Cache decrypted symlink targets in i_link for later use. Don't cache
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* symlink targets encoded without the key, since those become outdated
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* once the key is added. This pairs with the READ_ONCE() above and in
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* the VFS path lookup code.
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*/
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if (!has_key ||
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cmpxchg_release(&inode->i_link, NULL, pstr.name) != NULL)
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set_delayed_call(done, kfree_link, pstr.name);
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return pstr.name;
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err_kfree:
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@ -584,9 +584,30 @@ int fscrypt_get_encryption_info(struct inode *inode)
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}
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EXPORT_SYMBOL(fscrypt_get_encryption_info);
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/**
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* fscrypt_put_encryption_info - free most of an inode's fscrypt data
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*
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* Free the inode's fscrypt_info. Filesystems must call this when the inode is
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* being evicted. An RCU grace period need not have elapsed yet.
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*/
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void fscrypt_put_encryption_info(struct inode *inode)
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{
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put_crypt_info(inode->i_crypt_info);
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inode->i_crypt_info = NULL;
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}
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EXPORT_SYMBOL(fscrypt_put_encryption_info);
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/**
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* fscrypt_free_inode - free an inode's fscrypt data requiring RCU delay
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*
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* Free the inode's cached decrypted symlink target, if any. Filesystems must
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* call this after an RCU grace period, just before they free the inode.
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*/
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void fscrypt_free_inode(struct inode *inode)
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{
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if (IS_ENCRYPTED(inode) && S_ISLNK(inode->i_mode)) {
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kfree(inode->i_link);
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inode->i_link = NULL;
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}
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}
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EXPORT_SYMBOL(fscrypt_free_inode);
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@ -1110,6 +1110,9 @@ static int ext4_drop_inode(struct inode *inode)
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static void ext4_i_callback(struct rcu_head *head)
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{
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struct inode *inode = container_of(head, struct inode, i_rcu);
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fscrypt_free_inode(inode);
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kmem_cache_free(ext4_inode_cachep, EXT4_I(inode));
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}
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@ -1003,6 +1003,9 @@ static void f2fs_dirty_inode(struct inode *inode, int flags)
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static void f2fs_i_callback(struct rcu_head *head)
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{
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struct inode *inode = container_of(head, struct inode, i_rcu);
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fscrypt_free_inode(inode);
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kmem_cache_free(f2fs_inode_cachep, F2FS_I(inode));
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}
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@ -276,7 +276,10 @@ static void ubifs_i_callback(struct rcu_head *head)
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{
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struct inode *inode = container_of(head, struct inode, i_rcu);
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struct ubifs_inode *ui = ubifs_inode(inode);
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kfree(ui->data);
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fscrypt_free_inode(inode);
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kmem_cache_free(ubifs_inode_slab, ui);
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}
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@ -128,6 +128,7 @@ extern int fscrypt_inherit_context(struct inode *, struct inode *,
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/* keyinfo.c */
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extern int fscrypt_get_encryption_info(struct inode *);
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extern void fscrypt_put_encryption_info(struct inode *);
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extern void fscrypt_free_inode(struct inode *);
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/* fname.c */
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extern int fscrypt_setup_filename(struct inode *, const struct qstr *,
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@ -341,6 +342,10 @@ static inline void fscrypt_put_encryption_info(struct inode *inode)
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return;
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}
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static inline void fscrypt_free_inode(struct inode *inode)
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{
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}
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/* fname.c */
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static inline int fscrypt_setup_filename(struct inode *dir,
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const struct qstr *iname,
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