linux-kernel - [PATCH v2] usb: gadget: mass_storage: Fix cdrom data transfers on MAC-OS

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Date:   Sat, 27 Aug 2022 08:45:10 +0530
From:   Krishna Kurapati <quic_kriskura@...cinc.com>
To:     Alan Stern <stern@...land.harvard.edu>,
        Maxim Devaev <mdevaev@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Felipe Balbi <balbi@...nel.org>
CC:     <linux-usb@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <quic_jackp@...cinc.com>,
        Krishna Kurapati <quic_kriskura@...cinc.com>,
        <stable@...r.kernel.org>
Subject: [PATCH v2] usb: gadget: mass_storage: Fix cdrom data transfers on MAC-OS

During cdrom emulation, the response to read_toc command must contain
the cdrom address as the number of sectors (2048 byte sized blocks)
represented either as an absolute value (when MSF bit is '0') or in
terms of PMin/PSec/PFrame (when MSF bit is set to '1'). Incase of
cdrom, the fsg_lun_open call sets the sector size to 2048 bytes.

When MAC OS sends a read_toc request with MSF set to '1', the
store_cdrom_address assumes that the address being provided is the
LUN size represented in 512 byte sized blocks instead of 2048. It
tries to modify the address further to convert it to 2048 byte sized
blocks and store it in MSF format. This results in data transfer
failures as the cdrom address being provided in the read_toc response
is incorrect.

Fixes: 3f565a363cee ("usb: gadget: storage: adapt logic block size to bound block devices")
Cc: stable@...r.kernel.org
Signed-off-by: Krishna Kurapati <quic_kriskura@...cinc.com>
Acked-by: Alan Stern <stern@...land.harvard.edu>
---
 drivers/usb/gadget/function/storage_common.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/usb/gadget/function/storage_common.c b/drivers/usb/gadget/function/storage_common.c
index 03035db..208c6a9 100644
--- a/drivers/usb/gadget/function/storage_common.c
+++ b/drivers/usb/gadget/function/storage_common.c
@@ -294,8 +294,10 @@ EXPORT_SYMBOL_GPL(fsg_lun_fsync_sub);
 void store_cdrom_address(u8 *dest, int msf, u32 addr)
 {
 	if (msf) {
-		/* Convert to Minutes-Seconds-Frames */
-		addr >>= 2;		/* Convert to 2048-byte frames */
+		/*
+		 * Convert to Minutes-Seconds-Frames.
+		 * Sector size is already set to 2048 bytes.
+		 */
 		addr += 2*75;		/* Lead-in occupies 2 seconds */
 		dest[3] = addr % 75;	/* Frames */
 		addr /= 75;
-- 
2.7.4