[PATCH v3 1/4] ext4: add EXT4_INODE_HAS_XATTR_SPACE macro in xattr.h

From: Baokun Li <libaokun1@huawei.com>
To: <linux-ext4@vger.kernel.org>
Cc: <tytso@mit.edu>, <adilger.kernel@dilger.ca>, <jack@suse.cz>,
	<ritesh.list@gmail.com>, <lczerner@redhat.com>,
	<enwlinux@gmail.com>, <linux-kernel@vger.kernel.org>,
	<yi.zhang@huawei.com>, <yebin10@huawei.com>, <yukuai3@huawei.com>,
	<libaokun1@huawei.com>
Subject: [PATCH v3 1/4] ext4: add EXT4_INODE_HAS_XATTR_SPACE macro in xattr.h
Date: Thu, 16 Jun 2022 10:13:55 +0800	[thread overview]
Message-ID: <20220616021358.2504451-2-libaokun1@huawei.com> (raw)
In-Reply-To: <20220616021358.2504451-1-libaokun1@huawei.com>

When adding an xattr to an inode, we must ensure that the inode_size is
not less than EXT4_GOOD_OLD_INODE_SIZE + extra_isize + pad. Otherwise,
the end position may be greater than the start position, resulting in UAF.

Signed-off-by: Baokun Li <libaokun1@huawei.com>
---
 fs/ext4/xattr.h | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/fs/ext4/xattr.h b/fs/ext4/xattr.h
index 77efb9a627ad..f885f362add4 100644
--- a/fs/ext4/xattr.h
+++ b/fs/ext4/xattr.h
@@ -95,6 +95,19 @@ struct ext4_xattr_entry {
 
 #define EXT4_ZERO_XATTR_VALUE ((void *)-1)
 
+/*
+ * If we want to add an xattr to the inode, we should make sure that
+ * i_extra_isize is not 0 and that the inode size is not less than
+ * EXT4_GOOD_OLD_INODE_SIZE + extra_isize + pad.
+ *   EXT4_GOOD_OLD_INODE_SIZE   extra_isize header   entry   pad  data
+ * |--------------------------|------------|------|---------|---|-------|
+ */
+#define EXT4_INODE_HAS_XATTR_SPACE(inode)				\
+	((EXT4_I(inode)->i_extra_isize != 0) &&				\
+	 (EXT4_GOOD_OLD_INODE_SIZE + EXT4_I(inode)->i_extra_isize +	\
+	  sizeof(struct ext4_xattr_ibody_header) + EXT4_XATTR_PAD <=	\
+	  EXT4_INODE_SIZE((inode)->i_sb)))
+
 struct ext4_xattr_info {
 	const char *name;
 	const void *value;
-- 
2.31.1

