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

[Daniel Rosenberg <drosen@xxxxxxxxxx>]

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@xxxxxxxxxx>
---
 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