scsi: sr: Fix unintentional arithmetic wraparound

Running syzkaller with the newly reintroduced signed integer overflow
sanitizer produces this report:

[   65.194362] ------------[ cut here ]------------
[   65.197752] UBSAN: signed-integer-overflow in ../drivers/scsi/sr_ioctl.c:436:9
[   65.203607] -2147483648 * 177 cannot be represented in type 'int'
[   65.207911] CPU: 2 PID: 10416 Comm: syz-executor.1 Not tainted 6.8.0-rc2-00035-gb3ef86b5a957 #1
[   65.213585] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
[   65.219923] Call Trace:
[   65.221556]  <TASK>
[   65.223029]  dump_stack_lvl+0x93/0xd0
[   65.225573]  handle_overflow+0x171/0x1b0
[   65.228219]  sr_select_speed+0xeb/0xf0
[   65.230786]  ? __pm_runtime_resume+0xe6/0x130
[   65.233606]  sr_block_ioctl+0x15d/0x1d0
...

Historically, the signed integer overflow sanitizer did not work in the
kernel due to its interaction with `-fwrapv` but this has since been
changed [1] in the newest version of Clang. It was re-enabled in the kernel
with Commit 557f8c5 ("ubsan: Reintroduce signed overflow sanitizer").

Firstly, let's change the type of "speed" to unsigned long as
sr_select_speed()'s only caller passes in an unsigned long anyways.

$ git grep '\.select_speed'
|	drivers/scsi/sr.c:      .select_speed           = sr_select_speed,
...
|	static int cdrom_ioctl_select_speed(struct cdrom_device_info *cdi,
|	                unsigned long arg)
|	{
|	        ...
|	        return cdi->ops->select_speed(cdi, arg);
|	}

Next, let's add an extra check to make sure we don't exceed 0xffff/177
(350) since 0xffff is the max speed. This has two benefits: 1) we deal
with integer overflow before it happens and 2) we properly respect the
max speed of 0xffff. There are some "magic" numbers here but I did not
want to change more than what was necessary.

Link: llvm/llvm-project#82432 [1]
Closes: KSPP/linux#357
Cc: [email protected]
Signed-off-by: Justin Stitt <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Reviewed-by: Kees Cook <[email protected]>
Signed-off-by: Martin K. Petersen <[email protected]>

Author: JustinStitt

Documentation/cdrom/cdrom-standard.rst

@@ -217,7 +217,7 @@ current *struct* is::
 		int (*media_changed)(struct cdrom_device_info *, int);
 		int (*tray_move)(struct cdrom_device_info *, int);
 		int (*lock_door)(struct cdrom_device_info *, int);
-		int (*select_speed)(struct cdrom_device_info *, int);
+		int (*select_speed)(struct cdrom_device_info *, unsigned long);
 		int (*get_last_session) (struct cdrom_device_info *,
 					 struct cdrom_multisession *);
 		int (*get_mcn)(struct cdrom_device_info *, struct cdrom_mcn *);
@@ -396,7 +396,7 @@ action need be taken, and the return value should be 0.
 
 ::
 
-	int select_speed(struct cdrom_device_info *cdi, int speed)
+	int select_speed(struct cdrom_device_info *cdi, unsigned long speed)
 
 Some CD-ROM drives are capable of changing their head-speed. There
 are several reasons for changing the speed of a CD-ROM drive. Badly

drivers/scsi/sr.h

@@ -65,7 +65,7 @@ int sr_disk_status(struct cdrom_device_info *);
 int sr_get_last_session(struct cdrom_device_info *, struct cdrom_multisession *);
 int sr_get_mcn(struct cdrom_device_info *, struct cdrom_mcn *);
 int sr_reset(struct cdrom_device_info *);
-int sr_select_speed(struct cdrom_device_info *cdi, int speed);
+int sr_select_speed(struct cdrom_device_info *cdi, unsigned long speed);
 int sr_audio_ioctl(struct cdrom_device_info *, unsigned int, void *);
 
 int sr_is_xa(Scsi_CD *);

drivers/scsi/sr_ioctl.c

@@ -425,11 +425,14 @@ int sr_reset(struct cdrom_device_info *cdi)
 	return 0;
 }
 
-int sr_select_speed(struct cdrom_device_info *cdi, int speed)
+int sr_select_speed(struct cdrom_device_info *cdi, unsigned long speed)
 {
 	Scsi_CD *cd = cdi->handle;
 	struct packet_command cgc;
 
+	/* avoid exceeding the max speed or overflowing integer bounds */
+	speed = clamp(0, speed, 0xffff / 177);
+
 	if (speed == 0)
 		speed = 0xffff;	/* set to max */
 	else

include/linux/cdrom.h

@@ -77,7 +77,7 @@ struct cdrom_device_ops {
 				      unsigned int clearing, int slot);
 	int (*tray_move) (struct cdrom_device_info *, int);
 	int (*lock_door) (struct cdrom_device_info *, int);
-	int (*select_speed) (struct cdrom_device_info *, int);
+	int (*select_speed) (struct cdrom_device_info *, unsigned long);
 	int (*get_last_session) (struct cdrom_device_info *,
 				 struct cdrom_multisession *);
 	int (*get_mcn) (struct cdrom_device_info *,