diff options
author | Eric Biggers <ebiggers@google.com> | 2019-04-10 23:21:15 +0300 |
---|---|---|
committer | Theodore Ts'o <tytso@mit.edu> | 2019-04-17 19:43:29 +0300 |
commit | 2c58d548f5706d085c4b009f6abb945220460632 (patch) | |
tree | b263f432d3ad778b6970ebbb842bd0a577e88cdc /fs/crypto/hooks.c | |
parent | 4c4f7c19b3c721aed418bc97907b411608c5c6a0 (diff) | |
download | linux-2c58d548f5706d085c4b009f6abb945220460632.tar.xz |
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>
Diffstat (limited to 'fs/crypto/hooks.c')
-rw-r--r-- | fs/crypto/hooks.c | 40 |
1 files changed, 33 insertions, 7 deletions
diff --git a/fs/crypto/hooks.c b/fs/crypto/hooks.c index 042d5b44f4ed..2dc22549d724 100644 --- a/fs/crypto/hooks.c +++ b/fs/crypto/hooks.c @@ -189,11 +189,9 @@ 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 @@ -201,9 +199,20 @@ 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); @@ -212,7 +221,7 @@ 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. @@ -227,12 +236,18 @@ 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 = READ_ONCE(inode->i_link); + 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. @@ -240,6 +255,7 @@ 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 @@ -271,7 +287,17 @@ 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 the READ_ONCE() above and in + * the VFS path lookup code. + */ + 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: |