linux-kernel - [PATCH 4.9 050/101] ext4: add EXT4_INODE_HAS_XATTR

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Message-Id: <20220823080036.470780979@linuxfoundation.org>
Date:   Tue, 23 Aug 2022 10:03:23 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Baokun Li <libaokun1@...wei.com>,
        Jan Kara <jack@...e.cz>,
        "Ritesh Harjani (IBM)" <ritesh.list@...il.com>,
        Theodore Tso <tytso@....edu>
Subject: [PATCH 4.9 050/101] ext4: add EXT4_INODE_HAS_XATTR_SPACE macro in xattr.h

From: Baokun Li <libaokun1@...wei.com>

commit 179b14152dcb6a24c3415200603aebca70ff13af upstream.

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@...wei.com>
Reviewed-by: Jan Kara <jack@...e.cz>
Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@...il.com>
Link: https://lore.kernel.org/r/20220616021358.2504451-2-libaokun1@huawei.com
Signed-off-by: Theodore Ts'o <tytso@....edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 fs/ext4/xattr.h |   13 +++++++++++++
 1 file changed, 13 insertions(+)

--- a/fs/ext4/xattr.h
+++ b/fs/ext4/xattr.h
@@ -76,6 +76,19 @@ 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 {
 	int name_index;
 	const char *name;