xfs_inode_validate_cowextsize(
	struct xfs_mount		*mp,
	uint32_t			cowextsize,
	uint16_t			mode,
	uint16_t			flags,
	uint64_t			flags2)
{
	bool				rt_flag;
	bool				hint_flag;
	uint32_t			cowextsize_bytes;

	rt_flag = (flags & XFS_DIFLAG_REALTIME);
	hint_flag = (flags2 & XFS_DIFLAG2_COWEXTSIZE);
	cowextsize_bytes = XFS_FSB_TO_B(mp, cowextsize);

	if (hint_flag && !xfs_sb_version_hasreflink(&mp->m_sb))
		return __this_address;

	if (hint_flag && !(S_ISDIR(mode) || S_ISREG(mode)))
		return __this_address;

	if (hint_flag && cowextsize == 0)
		return __this_address;

	if (!hint_flag && cowextsize != 0)
		return __this_address;

	if (hint_flag && rt_flag)
		return __this_address;

	if (cowextsize_bytes % mp->m_sb.sb_blocksize)
		return __this_address;

	if (cowextsize > MAXEXTLEN)
		return __this_address;

	if (cowextsize > mp->m_sb.sb_agblocks / 2)
		return __this_address;

	return NULL;
}

The product dereferences a pointer that it expects to be valid but is NULL.