From 5cdc4a6950a883594e9640b1decb3fcf6222a594 Mon Sep 17 00:00:00 2001
From: lianzhi chang <changlianzhi@uniontech.com>
Date: Thu, 14 Jan 2021 15:57:41 +0800
Subject: [PATCH] udf: fix the problem that the disc content is not displayed
Git-commit: 5cdc4a6950a883594e9640b1decb3fcf6222a594
Patch-mainline: v5.11-rc5
References: bsc#1206644

When the capacity of the disc is too large (assuming the 4.7G
specification), the disc (UDF file system) will be burned
multiple times in the windows (Multisession Usage). When the
remaining capacity of the CD is less than 300M (estimated
value, for reference only), open the CD in the Linux system,
the content of the CD is displayed as blank (the kernel will
say "No VRS found"). Windows can display the contents of the
CD normally.
Through analysis, in the "fs/udf/super.c": udf_check_vsd
function, the actual value of VSD_MAX_SECTOR_OFFSET may
be much larger than 0x800000. According to the current code
logic, it is found that the type of sbi->s_session is "__s32",
 when the remaining capacity of the disc is less than 300M
(take a set of test values: sector=3154903040,
sbi->s_session=1540464, sb->s_blocksize_bits=11 ), the
calculation result of "sbi->s_session << sb->s_blocksize_bits"
 will overflow. Therefore, it is necessary to convert the
type of s_session to "loff_t" (when udf_check_vsd starts,
assign a value to _sector, which is also converted in this
way), so that the result will not overflow, and then the
content of the disc can be displayed normally.

Link: https://lore.kernel.org/r/20210114075741.30448-1-changlianzhi@uniontech.com
Signed-off-by: lianzhi chang <changlianzhi@uniontech.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Acked-by: Jan Kara <jack@suse.cz>

---
 fs/udf/super.c |    7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

--- a/fs/udf/super.c
+++ b/fs/udf/super.c
@@ -657,6 +657,7 @@ static loff_t udf_check_vsd(struct super
 	int nsr02 = 0;
 	int nsr03 = 0;
 	struct udf_sb_info *sbi;
+	loff_t session_offset;
 
 	sbi = UDF_SB(sb);
 	if (sb->s_blocksize < sizeof(struct volStructDesc))
@@ -664,7 +665,8 @@ static loff_t udf_check_vsd(struct super
 	else
 		sectorsize = sb->s_blocksize;
 
-	sector += (((loff_t)sbi->s_session) << sb->s_blocksize_bits);
+	session_offset = (loff_t)sbi->s_session << sb->s_blocksize_bits;
+	sector += session_offset;
 
 	udf_debug("Starting at sector %u (%lu byte sectors)\n",
 		  (unsigned int)(sector >> sb->s_blocksize_bits),
@@ -744,8 +746,7 @@ static loff_t udf_check_vsd(struct super
 		return nsr03;
 	else if (nsr02)
 		return nsr02;
-	else if (!bh && sector - (sbi->s_session << sb->s_blocksize_bits) ==
-			VSD_FIRST_SECTOR_OFFSET)
+	else if (!bh && sector - session_offset == VSD_FIRST_SECTOR_OFFSET)
 		return -1;
 	else
 		return 0;