ocfs2: validate inline xattr size and entry count in ocfs2_xattr_ibody_list

Add comprehensive validation of inline xattr metadata in
ocfs2_xattr_ibody_list() to prevent out-of-bounds access and
use-after-free bugs when processing corrupted inline xattrs.

The patch adds two critical validations:

1. Validates i_xattr_inline_size before use:
- Ensures it does not exceed block size
- Ensures it is at least large enough for xattr header
- Prevents pointer arithmetic with corrupted size values that could
point outside the inode block

2. Validates xattr entry count (xh_count):
- Calculates maximum entries that can fit in the inline space
- Rejects counts that exceed this limit
- Prevents out-of-bounds array access in subsequent code

Without these checks, a corrupted filesystem with invalid inline xattr
metadata can cause the code to access memory beyond the allocated space.
For example:
- A corrupted i_xattr_inline_size of 0 would cause header pointer
calculation to point past the end of the block
- A corrupted xh_count of 22 with inline_size of 256 would cause
array access 7 entries beyond the 15 that actually fit (the syzbot
reproducer used xh_count of 20041), leading to use-after-free when
accessing freed memory pages

The validation uses the correct inline_size (from di->i_xattr_inline_size)
rather than block size, ensuring accurate bounds checking for inline
xattrs specifically.

Link: https://lkml.kernel.org/r/[e-mail]
Link: https://lore.kernel.org/all/[e-mail]/ [v1]
Link: https://lore.kernel.org/all/[e-mail]/ [v2]
Link: https://lore.kernel.org/all/[e-mail]/ [v3]
Signed-off-by: Deepanshu Kartikey <[e-mail]>
Reported-by: [e-mail]
Closes: https://syzkaller.appspot.com/bug?extid=ab0ad25088673470d2d9
Tested-by: [e-mail]
Suggested-by: Heming Zhao <[e-mail]>
Reviewed-by: Heming Zhao <[e-mail]>
Acked-by: Joseph Qi <[e-mail]>
Cc: Mark Fasheh <[e-mail]>
Cc: Joel Becker <[e-mail]>
Cc: Junxiao Bi <[e-mail]>
Cc: Changwei Ge <[e-mail]>
Cc: Jun Piao <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

fs/ocfs2/xattr.c

···
 	struct ocfs2_xattr_header *header = NULL;
 	struct ocfs2_inode_info *oi = OCFS2_I(inode);
 	int ret = 0;
+	u16 xattr_count;
+	size_t max_entries;
+	u16 inline_size;
 
 	if (!(oi->ip_dyn_features & OCFS2_INLINE_XATTR_FL))
 		return ret;
 
+	inline_size = le16_to_cpu(di->i_xattr_inline_size);
+
+	/* Validate inline size is reasonable */
+	if (inline_size > inode->i_sb->s_blocksize ||
+	    inline_size < sizeof(struct ocfs2_xattr_header)) {
+		ocfs2_error(inode->i_sb,
+			    "Invalid xattr inline size %u in inode %llu\n",
+			    inline_size,
+			    (unsigned long long)OCFS2_I(inode)->ip_blkno);
+		return -EFSCORRUPTED;
+	}
+
 	header = (struct ocfs2_xattr_header *)
-		 ((void *)di + inode->i_sb->s_blocksize -
-		 le16_to_cpu(di->i_xattr_inline_size));
+		 ((void *)di + inode->i_sb->s_blocksize - inline_size);
+
+	xattr_count = le16_to_cpu(header->xh_count);
+	max_entries = (inline_size - sizeof(struct ocfs2_xattr_header)) /
+		       sizeof(struct ocfs2_xattr_entry);
+
+	if (xattr_count > max_entries) {
+		ocfs2_error(inode->i_sb,
+			    "xattr entry count %u exceeds maximum %zu in inode %llu\n",
+			    xattr_count, max_entries,
+			    (unsigned long long)OCFS2_I(inode)->ip_blkno);
+		return -EFSCORRUPTED;
+	}
 
 	ret = ocfs2_xattr_list_entries(inode, header, buffer, buffer_size);