udf: Avoid overflow when session starts at large offset

When session starts beyond offset 2^31 the arithmetics in
udf_check_vsd() would overflow. Make sure the computation is done in
large enough type.
Reported-by: NCezary Sliwa <sliwa@ifpan.edu.pl>
Signed-off-by: NJan Kara <jack@suse.cz>

fs/udf/super.c

@@ -703,7 +703,7 @@ static loff_t udf_check_vsd(struct super_block *sb)
 	else
 		sectorsize = sb->s_blocksize;
 
-	sector += (sbi->s_session << sb->s_blocksize_bits);
+	sector += (((loff_t)sbi->s_session) << sb->s_blocksize_bits);
 
 	udf_debug("Starting at sector %u (%ld byte sectors)\n",
 		  (unsigned int)(sector >> sb->s_blocksize_bits),