f2fs: sanity check checkpoint segno and blkoff

Make sure segno and blkoff read from raw image are valid.

Cc: stable@vger.kernel.org
Signed-off-by: Jin Qian <jinqian@google.com>
[Jaegeuk Kim: adjust minor coding style]
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
static unsigned char *__struct_ptr(struct f2fs_sb_info *sbi, int struct_type)
{
	if (struct_type == GC_THREAD)
		return (unsigned char *)sbi->gc_thread;
	else if (struct_type == SM_INFO)
		return (unsigned char *)SM_I(sbi);
	else if (struct_type == DCC_INFO)
		return (unsigned char *)SM_I(sbi)->dcc_info;
	else if (struct_type == NM_INFO)
		return (unsigned char *)NM_I(sbi);
	else if (struct_type == F2FS_SBI)
		return (unsigned char *)sbi;
#ifdef CONFIG_F2FS_FAULT_INJECTION
	else if (struct_type == FAULT_INFO_RATE ||
					struct_type == FAULT_INFO_TYPE)
		return (unsigned char *)&sbi->fault_info;
#endif
	return NULL;
}

static unsigned char *__struct_ptr(struct f2fs_sb_info *sbi, int struct_type)
{
	if (struct_type == GC_THREAD)
		return (unsigned char *)sbi->gc_thread;
	else if (struct_type == SM_INFO)
		return (unsigned char *)SM_I(sbi);
	else if (struct_type == DCC_INFO)
		return (unsigned char *)SM_I(sbi)->dcc_info;
	else if (struct_type == NM_INFO)
		return (unsigned char *)NM_I(sbi);
	else if (struct_type == F2FS_SBI)
		return (unsigned char *)sbi;
#ifdef CONFIG_F2FS_FAULT_INJECTION
	else if (struct_type == FAULT_INFO_RATE ||
					struct_type == FAULT_INFO_TYPE)
		return (unsigned char *)&sbi->fault_info;
#endif
	return NULL;
}
