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[RFC,v6,04/20] fscrypt: add fscrypt_context_for_new_inode

Message ID 20210413175052.163865-5-jlayton@kernel.org (mailing list archive)
State New
Headers show
Series ceph+fscrypt: context, filename and symlink support | expand

Commit Message

Jeff Layton April 13, 2021, 5:50 p.m. UTC
Most filesystems just call fscrypt_set_context on new inodes, which
usually causes a setxattr. That's a bit late for ceph, which can send
along a full blob of xattrs with the create request.

That allows us to avoid race windows that where the new inode could be
seen by other clients without the crypto context attached. It also
avoids the separate round trip to the server.

Refactor the code a bit to allow us to create a new crypto context,
attach it to the inode, and write it to the buffer, but without calling
set_context on it. ceph can later use this to marshal the context into
the buffer we send along with the create request.

Signed-off-by: Jeff Layton <jlayton@kernel.org>
---
 fs/crypto/policy.c      | 34 ++++++++++++++++++++++++++++------
 include/linux/fscrypt.h |  1 +
 2 files changed, 29 insertions(+), 6 deletions(-)
diff mbox series

Patch

diff --git a/fs/crypto/policy.c b/fs/crypto/policy.c
index ed3d623724cd..6a895a31560f 100644
--- a/fs/crypto/policy.c
+++ b/fs/crypto/policy.c
@@ -664,6 +664,31 @@  const union fscrypt_policy *fscrypt_policy_to_inherit(struct inode *dir)
 	return fscrypt_get_dummy_policy(dir->i_sb);
 }
 
+/**
+ * fscrypt_context_for_new_inode() - create an encryption context for a new inode
+ * @ctx: where context should be written
+ * @inode: inode from which to fetch policy and nonce
+ *
+ * Given an in-core "prepared" (via fscrypt_prepare_new_inode) inode,
+ * generate a new context and write it to ctx. ctx _must_ be at least
+ * FSCRYPT_SET_CONTEXT_MAX_SIZE bytes.
+ *
+ * Returns size of the resulting context or a negative error code.
+ */
+int fscrypt_context_for_new_inode(void *ctx, struct inode *inode)
+{
+	struct fscrypt_info *ci = inode->i_crypt_info;
+
+	BUILD_BUG_ON(sizeof(union fscrypt_context) != FSCRYPT_SET_CONTEXT_MAX_SIZE);
+
+	/* fscrypt_prepare_new_inode() should have set up the key already. */
+	if (WARN_ON_ONCE(!ci))
+		return -ENOKEY;
+
+	return fscrypt_new_context(ctx, &ci->ci_policy, ci->ci_nonce);
+}
+EXPORT_SYMBOL_GPL(fscrypt_context_for_new_inode);
+
 /**
  * fscrypt_set_context() - Set the fscrypt context of a new inode
  * @inode: a new inode
@@ -680,12 +705,9 @@  int fscrypt_set_context(struct inode *inode, void *fs_data)
 	union fscrypt_context ctx;
 	int ctxsize;
 
-	/* fscrypt_prepare_new_inode() should have set up the key already. */
-	if (WARN_ON_ONCE(!ci))
-		return -ENOKEY;
-
-	BUILD_BUG_ON(sizeof(ctx) != FSCRYPT_SET_CONTEXT_MAX_SIZE);
-	ctxsize = fscrypt_new_context(&ctx, &ci->ci_policy, ci->ci_nonce);
+	ctxsize = fscrypt_context_for_new_inode(&ctx, inode);
+	if (ctxsize < 0)
+		return ctxsize;
 
 	/*
 	 * This may be the first time the inode number is available, so do any
diff --git a/include/linux/fscrypt.h b/include/linux/fscrypt.h
index b5c31baaa8bf..087fa87bca0b 100644
--- a/include/linux/fscrypt.h
+++ b/include/linux/fscrypt.h
@@ -178,6 +178,7 @@  int fscrypt_ioctl_get_policy(struct file *filp, void __user *arg);
 int fscrypt_ioctl_get_policy_ex(struct file *filp, void __user *arg);
 int fscrypt_ioctl_get_nonce(struct file *filp, void __user *arg);
 int fscrypt_has_permitted_context(struct inode *parent, struct inode *child);
+int fscrypt_context_for_new_inode(void *ctx, struct inode *inode);
 int fscrypt_set_context(struct inode *inode, void *fs_data);
 
 struct fscrypt_dummy_policy {