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

[Baokun Li <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