Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755201AbdC1MlA (ORCPT ); Tue, 28 Mar 2017 08:41:00 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:60088 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932102AbdC1Mk5 (ORCPT ); Tue, 28 Mar 2017 08:40:57 -0400 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Eric Biggers , Theodore Tso , Michael Halcrow Subject: [PATCH 4.10 082/111] fscrypt: remove broken support for detecting keyring key revocation Date: Tue, 28 Mar 2017 14:31:08 +0200 Message-Id: <20170328122919.081362833@linuxfoundation.org> X-Mailer: git-send-email 2.12.1 In-Reply-To: <20170328122915.640228468@linuxfoundation.org> References: <20170328122915.640228468@linuxfoundation.org> User-Agent: quilt/0.65 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 7859 Lines: 245 4.10-stable review patch. If anyone has any objections, please let me know. ------------------ From: Eric Biggers commit 1b53cf9815bb4744958d41f3795d5d5a1d365e2d upstream. Filesystem encryption ostensibly supported revoking a keyring key that had been used to "unlock" encrypted files, causing those files to become "locked" again. This was, however, buggy for several reasons, the most severe of which was that when key revocation happened to be detected for an inode, its fscrypt_info was immediately freed, even while other threads could be using it for encryption or decryption concurrently. This could be exploited to crash the kernel or worse. This patch fixes the use-after-free by removing the code which detects the keyring key having been revoked, invalidated, or expired. Instead, an encrypted inode that is "unlocked" now simply remains unlocked until it is evicted from memory. Note that this is no worse than the case for block device-level encryption, e.g. dm-crypt, and it still remains possible for a privileged user to evict unused pages, inodes, and dentries by running 'sync; echo 3 > /proc/sys/vm/drop_caches', or by simply unmounting the filesystem. In fact, one of those actions was already needed anyway for key revocation to work even somewhat sanely. This change is not expected to break any applications. In the future I'd like to implement a real API for fscrypt key revocation that interacts sanely with ongoing filesystem operations --- waiting for existing operations to complete and blocking new operations, and invalidating and sanitizing key material and plaintext from the VFS caches. But this is a hard problem, and for now this bug must be fixed. This bug affected almost all versions of ext4, f2fs, and ubifs encryption, and it was potentially reachable in any kernel configured with encryption support (CONFIG_EXT4_ENCRYPTION=y, CONFIG_EXT4_FS_ENCRYPTION=y, CONFIG_F2FS_FS_ENCRYPTION=y, or CONFIG_UBIFS_FS_ENCRYPTION=y). Note that older kernels did not use the shared fs/crypto/ code, but due to the potential security implications of this bug, it may still be worthwhile to backport this fix to them. Fixes: b7236e21d55f ("ext4 crypto: reorganize how we store keys in the inode") Signed-off-by: Eric Biggers Signed-off-by: Theodore Ts'o Acked-by: Michael Halcrow Signed-off-by: Greg Kroah-Hartman --- fs/crypto/crypto.c | 10 -------- fs/crypto/fname.c | 2 - fs/crypto/fscrypt_private.h | 4 --- fs/crypto/keyinfo.c | 52 +++++++------------------------------------- 4 files changed, 11 insertions(+), 57 deletions(-) --- a/fs/crypto/crypto.c +++ b/fs/crypto/crypto.c @@ -394,7 +394,6 @@ EXPORT_SYMBOL(fscrypt_zeroout_range); static int fscrypt_d_revalidate(struct dentry *dentry, unsigned int flags) { struct dentry *dir; - struct fscrypt_info *ci; int dir_has_key, cached_with_key; if (flags & LOOKUP_RCU) @@ -406,18 +405,11 @@ static int fscrypt_d_revalidate(struct d return 0; } - ci = d_inode(dir)->i_crypt_info; - if (ci && ci->ci_keyring_key && - (ci->ci_keyring_key->flags & ((1 << KEY_FLAG_INVALIDATED) | - (1 << KEY_FLAG_REVOKED) | - (1 << KEY_FLAG_DEAD)))) - ci = NULL; - /* this should eventually be an flag in d_flags */ spin_lock(&dentry->d_lock); cached_with_key = dentry->d_flags & DCACHE_ENCRYPTED_WITH_KEY; spin_unlock(&dentry->d_lock); - dir_has_key = (ci != NULL); + dir_has_key = (d_inode(dir)->i_crypt_info != NULL); dput(dir); /* --- a/fs/crypto/fname.c +++ b/fs/crypto/fname.c @@ -350,7 +350,7 @@ int fscrypt_setup_filename(struct inode fname->disk_name.len = iname->len; return 0; } - ret = fscrypt_get_crypt_info(dir); + ret = fscrypt_get_encryption_info(dir); if (ret && ret != -EOPNOTSUPP) return ret; --- a/fs/crypto/fscrypt_private.h +++ b/fs/crypto/fscrypt_private.h @@ -67,7 +67,6 @@ struct fscrypt_info { u8 ci_filename_mode; u8 ci_flags; struct crypto_skcipher *ci_ctfm; - struct key *ci_keyring_key; u8 ci_master_key[FS_KEY_DESCRIPTOR_SIZE]; }; @@ -87,7 +86,4 @@ struct fscrypt_completion_result { /* crypto.c */ int fscrypt_initialize(unsigned int cop_flags); -/* keyinfo.c */ -extern int fscrypt_get_crypt_info(struct inode *); - #endif /* _FSCRYPT_PRIVATE_H */ --- a/fs/crypto/keyinfo.c +++ b/fs/crypto/keyinfo.c @@ -99,6 +99,7 @@ static int validate_user_key(struct fscr kfree(full_key_descriptor); if (IS_ERR(keyring_key)) return PTR_ERR(keyring_key); + down_read(&keyring_key->sem); if (keyring_key->type != &key_type_logon) { printk_once(KERN_WARNING @@ -106,11 +107,9 @@ static int validate_user_key(struct fscr res = -ENOKEY; goto out; } - down_read(&keyring_key->sem); ukp = user_key_payload(keyring_key); if (ukp->datalen != sizeof(struct fscrypt_key)) { res = -EINVAL; - up_read(&keyring_key->sem); goto out; } master_key = (struct fscrypt_key *)ukp->data; @@ -121,17 +120,11 @@ static int validate_user_key(struct fscr "%s: key size incorrect: %d\n", __func__, master_key->size); res = -ENOKEY; - up_read(&keyring_key->sem); goto out; } res = derive_key_aes(ctx->nonce, master_key->raw, raw_key); - up_read(&keyring_key->sem); - if (res) - goto out; - - crypt_info->ci_keyring_key = keyring_key; - return 0; out: + up_read(&keyring_key->sem); key_put(keyring_key); return res; } @@ -173,12 +166,11 @@ static void put_crypt_info(struct fscryp if (!ci) return; - key_put(ci->ci_keyring_key); crypto_free_skcipher(ci->ci_ctfm); kmem_cache_free(fscrypt_info_cachep, ci); } -int fscrypt_get_crypt_info(struct inode *inode) +int fscrypt_get_encryption_info(struct inode *inode) { struct fscrypt_info *crypt_info; struct fscrypt_context ctx; @@ -188,21 +180,15 @@ int fscrypt_get_crypt_info(struct inode u8 *raw_key = NULL; int res; + if (inode->i_crypt_info) + return 0; + res = fscrypt_initialize(inode->i_sb->s_cop->flags); if (res) return res; if (!inode->i_sb->s_cop->get_context) return -EOPNOTSUPP; -retry: - crypt_info = ACCESS_ONCE(inode->i_crypt_info); - if (crypt_info) { - if (!crypt_info->ci_keyring_key || - key_validate(crypt_info->ci_keyring_key) == 0) - return 0; - fscrypt_put_encryption_info(inode, crypt_info); - goto retry; - } res = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx)); if (res < 0) { @@ -230,7 +216,6 @@ retry: crypt_info->ci_data_mode = ctx.contents_encryption_mode; crypt_info->ci_filename_mode = ctx.filenames_encryption_mode; crypt_info->ci_ctfm = NULL; - crypt_info->ci_keyring_key = NULL; memcpy(crypt_info->ci_master_key, ctx.master_key_descriptor, sizeof(crypt_info->ci_master_key)); @@ -286,14 +271,8 @@ got_key: if (res) goto out; - kzfree(raw_key); - raw_key = NULL; - if (cmpxchg(&inode->i_crypt_info, NULL, crypt_info) != NULL) { - put_crypt_info(crypt_info); - goto retry; - } - return 0; - + if (cmpxchg(&inode->i_crypt_info, NULL, crypt_info) == NULL) + crypt_info = NULL; out: if (res == -ENOKEY) res = 0; @@ -301,6 +280,7 @@ out: kzfree(raw_key); return res; } +EXPORT_SYMBOL(fscrypt_get_encryption_info); void fscrypt_put_encryption_info(struct inode *inode, struct fscrypt_info *ci) { @@ -318,17 +298,3 @@ void fscrypt_put_encryption_info(struct put_crypt_info(ci); } EXPORT_SYMBOL(fscrypt_put_encryption_info); - -int fscrypt_get_encryption_info(struct inode *inode) -{ - struct fscrypt_info *ci = inode->i_crypt_info; - - if (!ci || - (ci->ci_keyring_key && - (ci->ci_keyring_key->flags & ((1 << KEY_FLAG_INVALIDATED) | - (1 << KEY_FLAG_REVOKED) | - (1 << KEY_FLAG_DEAD))))) - return fscrypt_get_crypt_info(inode); - return 0; -} -EXPORT_SYMBOL(fscrypt_get_encryption_info);