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fscrypt: remove broken support for detecting keyring key revocation 

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the keyring key having been revoked, invalidated, or expired.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")
Cc: stable@vger.kernel.org # v4.2+
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Acked-by: Michael Halcrow <mhalcrow@google.com>
[haggertk]: Backport to 3.4/msm8974
CVE-2017-7374
Signed-off-by: Kevin F. Haggerty <haggertk@lineageos.org>

Change-Id: I2204233b893960f4e0e33c58f6135920724e84b1
This commit is contained in:
Eric Biggers 2017-02-21 15:07:11 -08:00 committed by Francescodario Cuzzocrea
parent 61b8ecee26
commit d02517c58a
4 changed files with 11 additions and 54 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

10
fs/crypto/crypto.c
View File

@ -350,7 +350,6 @@ 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)
@ -362,18 +361,11 @@ static int fscrypt_d_revalidate(struct dentry *dentry, unsigned int flags)
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);
/*

2
fs/crypto/fname.c
View File

@ -363,7 +363,7 @@ int fscrypt_setup_filename(struct inode *dir, const struct qstr *iname,
fname->disk_name.len = iname->len;
return 0;
}
ret = get_crypt_info(dir);
ret = fscrypt_get_encryption_info(dir);
if (ret && ret != -EOPNOTSUPP)
return ret;

52
fs/crypto/keyinfo.c
View File

@ -106,6 +106,7 @@ static int validate_user_key(struct fscrypt_info *crypt_info,
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
@ -113,11 +114,9 @@ static int validate_user_key(struct fscrypt_info *crypt_info,
res = -ENOKEY;
goto out;
}
down_read(&keyring_key->sem);
ukp = ((struct user_key_payload *)keyring_key->payload.data);
if (ukp->datalen != sizeof(struct fscrypt_key)) {
res = -EINVAL;
up_read(&keyring_key->sem);
goto out;
}
master_key = (struct fscrypt_key *)ukp->data;
@ -128,17 +127,11 @@ static int validate_user_key(struct fscrypt_info *crypt_info,
"%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;
}
@ -148,13 +141,11 @@ static void put_crypt_info(struct fscrypt_info *ci)
if (!ci)
return;
if (ci->ci_keyring_key)
key_put(ci->ci_keyring_key);
crypto_free_ablkcipher(ci->ci_ctfm);
kmem_cache_free(fscrypt_info_cachep, ci);
}
int get_crypt_info(struct inode *inode)
int fscrypt_get_encryption_info(struct inode *inode)
{
struct fscrypt_info *crypt_info;
struct fscrypt_context ctx;
@ -164,21 +155,15 @@ int get_crypt_info(struct inode *inode)
u8 mode;
int res;
if (inode->i_crypt_info)
return 0;
res = fscrypt_initialize();
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) {
@ -200,7 +185,6 @@ 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));
if (S_ISREG(inode->i_mode))
@ -263,13 +247,8 @@ got_key:
if (res)
goto out;
memzero_explicit(raw_key, sizeof(raw_key));
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;
@ -277,6 +256,7 @@ out:
memzero_explicit(raw_key, sizeof(raw_key));
return res;
}
EXPORT_SYMBOL(fscrypt_get_encryption_info);
void fscrypt_put_encryption_info(struct inode *inode, struct fscrypt_info *ci)
{
@ -294,17 +274,3 @@ void fscrypt_put_encryption_info(struct inode *inode, struct fscrypt_info *ci)
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 get_crypt_info(inode);
return 0;
}
EXPORT_SYMBOL(fscrypt_get_encryption_info);

1
include/linux/fscrypto.h
View File

@ -77,7 +77,6 @@ struct fscrypt_info {
u8 ci_filename_mode;
u8 ci_flags;
struct crypto_ablkcipher *ci_ctfm;
struct key *ci_keyring_key;
u8 ci_master_key[FS_KEY_DESCRIPTOR_SIZE];
};