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Message-ID: <20240508-b4-b4-sio-sr_select_speed-v2-1-00b68f724290@google.com>
Date: Wed, 08 May 2024 17:22:51 +0000
From: Justin Stitt <justinstitt@...gle.com>
To: "James E.J. Bottomley" <James.Bottomley@...senPartnership.com>, 
	"Martin K. Petersen" <martin.petersen@...cle.com>, Nathan Chancellor <nathan@...nel.org>, 
	Bill Wendling <morbo@...gle.com>
Cc: linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org, 
	llvm@...ts.linux.dev, linux-hardening@...r.kernel.org, 
	Justin Stitt <justinstitt@...gle.com>
Subject: [PATCH v2] 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 557f8c582a9ba8ab ("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: https://github.com/llvm/llvm-project/pull/82432 [1]
Closes: https://github.com/KSPP/linux/issues/357
Cc: linux-hardening@...r.kernel.org
Signed-off-by: Justin Stitt <justinstitt@...gle.com>
---
Changes in v2:
- change @speed type from int to unsigned long and use a clamp (thanks Kees)
- also update documentation to avoid confusion
- Link to v1: https://lore.kernel.org/r/20240508-b4-b4-sio-sr_select_speed-v1-1-968906b908b7@google.com
---
Here's the syzkaller reproducer:
r0 = openat$cdrom(0xffffffffffffff9c, &(0x7f0000000140), 0x800, 0x0)
ioctl$CDROM_SELECT_SPEED(r0, 0x5322, 0x7ee9f7c1)

... which was used against Kees' tree here (v6.8rc2):
https://git.kernel.org/pub/scm/linux/kernel/git/kees/linux.git/log/?h=wip/v6.9-rc2/unsigned-overflow-sanitizer

... with this config:
https://gist.github.com/JustinStitt/824976568b0f228ccbcbe49f3dee9bf4
---
 Documentation/cdrom/cdrom-standard.rst | 4 ++--
 drivers/scsi/sr.h                      | 2 +-
 drivers/scsi/sr_ioctl.c                | 5 ++++-
 include/linux/cdrom.h                  | 2 +-
 4 files changed, 8 insertions(+), 5 deletions(-)

diff --git a/Documentation/cdrom/cdrom-standard.rst b/Documentation/cdrom/cdrom-standard.rst
index 7964fe134277..6c1303cff159 100644
--- a/Documentation/cdrom/cdrom-standard.rst
+++ b/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
diff --git a/drivers/scsi/sr.h b/drivers/scsi/sr.h
index 1175f2e213b5..dc899277b3a4 100644
--- a/drivers/scsi/sr.h
+++ b/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 *);
diff --git a/drivers/scsi/sr_ioctl.c b/drivers/scsi/sr_ioctl.c
index 5b0b35e60e61..a0d2556a27bb 100644
--- a/drivers/scsi/sr_ioctl.c
+++ b/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
diff --git a/include/linux/cdrom.h b/include/linux/cdrom.h
index 98c6fd0b39b6..fdfb61ccf55a 100644
--- a/include/linux/cdrom.h
+++ b/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 *,

---
base-commit: 0106679839f7c69632b3b9833c3268c316c0a9fc
change-id: 20240507-b4-b4-sio-sr_select_speed-e68c0d426891

Best regards,
--
Justin Stitt <justinstitt@...gle.com>

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