ext4: use fscrypt_prepare_new_inode() and fscrypt_set_context()

Convert ext4 to use the new functions fscrypt_prepare_new_inode() and
fscrypt_set_context().  This avoids calling
fscrypt_get_encryption_info() from within a transaction, which can
deadlock because fscrypt_get_encryption_info() isn't GFP_NOFS-safe.

For more details about this problem, see the earlier patch
"fscrypt: add fscrypt_prepare_new_inode() and fscrypt_set_context()".

Link: https://lore.kernel.org/r/20200917041136.178600-4-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>

fs/ext4/ialloc.c

@@ -819,7 +819,7 @@ struct inode *__ext4_new_inode(handle_t *handle, struct inode *dir,
 	ext4_group_t i;
 	ext4_group_t flex_group;
 	struct ext4_group_info *grp;
-	int encrypt = 0;
+	bool encrypt = false;
 
 	/* Cannot create files in a deleted directory */
 	if (!dir || !dir->i_nlink)
@@ -831,24 +831,6 @@ struct inode *__ext4_new_inode(handle_t *handle, struct inode *dir,
 	if (unlikely(ext4_forced_shutdown(sbi)))
 		return ERR_PTR(-EIO);
 
-	if ((IS_ENCRYPTED(dir) || DUMMY_ENCRYPTION_ENABLED(sbi)) &&
-	    (S_ISREG(mode) || S_ISDIR(mode) || S_ISLNK(mode)) &&
-	    !(i_flags & EXT4_EA_INODE_FL)) {
-		err = fscrypt_get_encryption_info(dir);
-		if (err)
-			return ERR_PTR(err);
-		if (!fscrypt_has_encryption_key(dir))
-			return ERR_PTR(-ENOKEY);
-		encrypt = 1;
-	}
-
-	if (!handle && sbi->s_journal && !(i_flags & EXT4_EA_INODE_FL)) {
-		ret2 = ext4_xattr_credits_for_new_inode(dir, mode, encrypt);
-		if (ret2 < 0)
-			return ERR_PTR(ret2);
-		nblocks += ret2;
-	}
-
 	ngroups = ext4_get_groups_count(sb);
 	trace_ext4_request_inode(dir, mode);
 	inode = new_inode(sb);
@@ -878,10 +860,25 @@ struct inode *__ext4_new_inode(handle_t *handle, struct inode *dir,
 	else
 		ei->i_projid = make_kprojid(&init_user_ns, EXT4_DEF_PROJID);
 
+	if (!(i_flags & EXT4_EA_INODE_FL)) {
+		err = fscrypt_prepare_new_inode(dir, inode, &encrypt);
+		if (err)
+			goto out;
+	}
+
 	err = dquot_initialize(inode);
 	if (err)
 		goto out;
 
+	if (!handle && sbi->s_journal && !(i_flags & EXT4_EA_INODE_FL)) {
+		ret2 = ext4_xattr_credits_for_new_inode(dir, mode, encrypt);
+		if (ret2 < 0) {
+			err = ret2;
+			goto out;
+		}
+		nblocks += ret2;
+	}
+
 	if (!goal)
 		goal = sbi->s_inode_goal;
 
@@ -1174,7 +1171,7 @@ got:
 	 * prevent its deduplication.
 	 */
 	if (encrypt) {
-		err = fscrypt_inherit_context(dir, inode, handle, true);
+		err = fscrypt_set_context(inode, handle);
 		if (err)
 			goto fail_free_drop;
 	}