[PATCH 2/8] fscrypt: Don't allow v1 policies with casefolding

Daniel Rosenberg
2019-12-03T05:12:04Z

Casefolding requires a derived key for computing the siphash.
This is available for v2 policies, but not v1, so we disallow it for v1.

Signed-off-by: Daniel Rosenberg <drosen@google.com>
---
fs/crypto/policy.c | 26 +++++++++++++++++++++++---
fs/inode.c | 8 ++++++++
include/linux/fscrypt.h | 7 +++++++
3 files changed, 38 insertions(+), 3 deletions(-)

diff --git a/fs/crypto/policy.c b/fs/crypto/policy.c
index 96f528071bed..94d96d3212d6 100644
--- a/fs/crypto/policy.c
+++ b/fs/crypto/policy.c
@@ -67,9 +67,9 @@ static bool supported_iv_ino_lblk_64_policy(
* fscrypt_supported_policy - check whether an encryption policy is supported
*
* Given an encryption policy, check whether all its encryption modes and other
- * settings are supported by this kernel. (But we don't currently don't check
- * for crypto API support here, so attempting to use an algorithm not configured
- * into the crypto API will still fail later.)
+ * settings are supported by this kernel on the given inode. (But we don't
+ * currently don't check for crypto API support here, so attempting to use an
+ * algorithm not configured into the crypto API will still fail later.)
*
* Return: %true if supported, else %false
*/
@@ -97,6 +97,12 @@ bool fscrypt_supported_policy(const union fscrypt_policy *policy_u,
return false;
}

+ if (IS_CASEFOLDED(inode)) {
+ fscrypt_warn(inode,
+ "v1 policy does not support casefolded directories");
+ return false;
+ }
+
return true;
}
case FSCRYPT_POLICY_V2: {
@@ -530,3 +536,17 @@ int fscrypt_inherit_context(struct inode *parent, struct inode *child,
return preload ? fscrypt_get_encryption_info(child): 0;
}
EXPORT_SYMBOL(fscrypt_inherit_context);
+
+int fscrypt_set_casefolding_allowed(struct inode *inode)
+{
+ union fscrypt_policy policy;
+ int ret = fscrypt_get_policy(inode, &policy);
+
+ if (ret < 0)
+ return ret;
+
+ if (policy.version == FSCRYPT_POLICY_V2)
+ return 0;
+ else
+ return -EINVAL;
+}
diff --git a/fs/inode.c b/fs/inode.c
index fef457a42882..b615ec272a1e 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -20,6 +20,7 @@
#include <linux/ratelimit.h>
#include <linux/list_lru.h>
#include <linux/iversion.h>
+#include <linux/fscrypt.h>
#include <trace/events/writeback.h>
#include "internal.h"

@@ -2245,6 +2246,13 @@ int vfs_ioc_setflags_prepare(struct inode *inode, unsigned int oldflags,
!capable(CAP_LINUX_IMMUTABLE))
return -EPERM;

+ /*
+ * When a directory is encrypted, the CASEFOLD flag can only be turned
+ * on if the fscrypt policy supports it.
+ */
+ if (IS_ENCRYPTED(inode) && (flags & ~oldflags & FS_CASEFOLD_FL))
+ return fscrypt_set_casefolding_allowed(inode);
+
return 0;
}
EXPORT_SYMBOL(vfs_ioc_setflags_prepare);
diff --git a/include/linux/fscrypt.h b/include/linux/fscrypt.h
index e13ff68a99f0..028aed925e51 100644
--- a/include/linux/fscrypt.h
+++ b/include/linux/fscrypt.h
@@ -127,6 +127,8 @@ extern int fscrypt_ioctl_get_policy_ex(struct file *, void __user *);
extern int fscrypt_has_permitted_context(struct inode *, struct inode *);
extern int fscrypt_inherit_context(struct inode *, struct inode *,
void *, bool);
+extern int fscrypt_set_casefolding_allowed(struct inode *inode);
+
/* keyring.c */
extern void fscrypt_sb_free(struct super_block *sb);
extern int fscrypt_ioctl_add_key(struct file *filp, void __user *arg);
@@ -361,6 +363,11 @@ static inline int fscrypt_inherit_context(struct inode *parent,
return -EOPNOTSUPP;
}

+static inline int fscrypt_set_casefolding_allowed(struct inode *inode)
+{
+ return 0;
+}
+
/* keyring.c */
static inline void fscrypt_sb_free(struct super_block *sb)
{
--
2.24.0.393.g34dc348eaf-goog