[PATCH 4.9 102/144] scsi: 3w-9xxx: fix a missing-check bug

[Greg Kroah-Hartman]

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Wenwen Wang <wang6495@xxxxxxx>

[ Upstream commit c9318a3e0218bc9dacc25be46b9eec363259536f ]

In twa_chrdev_ioctl(), the ioctl driver command is firstly copied from
the userspace pointer 'argp' and saved to the kernel object
'driver_command'.  Then a security check is performed on the data buffer
size indicated by 'driver_command', which is
'driver_command.buffer_length'. If the security check is passed, the
entire ioctl command is copied again from the 'argp' pointer and saved
to the kernel object 'tw_ioctl'. Then, various operations are performed
on 'tw_ioctl' according to the 'cmd'. Given that the 'argp' pointer
resides in userspace, a malicious userspace process can race to change
the buffer size between the two copies. This way, the user can bypass
the security check and inject invalid data buffer size. This can cause
potential security issues in the following execution.

This patch checks for capable(CAP_SYS_ADMIN) in twa_chrdev_open()t o
avoid the above issues.

Signed-off-by: Wenwen Wang <wang6495@xxxxxxx>
Acked-by: Adam Radford <aradford@xxxxxxxxx>
Signed-off-by: Martin K. Petersen <martin.petersen@xxxxxxxxxx>
Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 drivers/scsi/3w-9xxx.c |    5 +++++
 1 file changed, 5 insertions(+)

--- a/drivers/scsi/3w-9xxx.c
+++ b/drivers/scsi/3w-9xxx.c
@@ -889,6 +889,11 @@ static int twa_chrdev_open(struct inode
 	unsigned int minor_number;
 	int retval = TW_IOCTL_ERROR_OS_ENODEV;
 
+	if (!capable(CAP_SYS_ADMIN)) {
+		retval = -EACCES;
+		goto out;
+	}
+
 	minor_number = iminor(inode);
 	if (minor_number >= twa_device_extension_count)
 		goto out;