CVE-2011-4127: Permissions, Privileges, and Access Controls (CWE-264)
value: The Linux kernel before 3.2.2 does not properly restrict SG_IO ioctl calls, which allows local users to bypass intended restrictions on disk read and write operations by sending a SCSI command to (1) a partition block device or (2) an LVM volume.
CWE description: Weaknesses in this category are related to the management of permissions, privileges, and other security features that are used to perform access control.
Published: 2012-07-03T16:40Z
Repository: https://github.com/torvalds/linux
Language: C
Files changed: block/scsi_ioctl.c, drivers/scsi/sd.c, include/linux/blkdev.h
Commit date: 2012-01-14 15:07:24 -0800
Commit message: block: fail SCSI passthrough ioctls on partition devices

Linux allows executing the SG_IO ioctl on a partition or LVM volume, and
will pass the command to the underlying block device.  This is
well-known, but it is also a large security problem when (via Unix
permissions, ACLs, SELinux or a combination thereof) a program or user
needs to be granted access only to part of the disk.

This patch lets partitions forward a small set of harmless ioctls;
others are logged with printk so that we can see which ioctls are
actually sent.  In my tests only CDROM_GET_CAPABILITY actually occurred.
Of course it was being sent to a (partition on a) hard disk, so it would
have failed with ENOTTY and the patch isn't changing anything in
practice.  Still, I'm treating it specially to avoid spamming the logs.

In principle, this restriction should include programs running with
CAP_SYS_RAWIO.  If for example I let a program access /dev/sda2 and
/dev/sdb, it still should not be able to read/write outside the
boundaries of /dev/sda2 independent of the capabilities.  However, for
now programs with CAP_SYS_RAWIO will still be allowed to send the
ioctls.  Their actions will still be logged.

This patch does not affect the non-libata IDE driver.  That driver
however already tests for bd != bd->bd_contains before issuing some
ioctl; it could be restricted further to forbid these ioctls even for
programs running with CAP_SYS_ADMIN/CAP_SYS_RAWIO.

Cc: linux-scsi@vger.kernel.org
Cc: Jens Axboe <axboe@kernel.dk>
Cc: James Bottomley <JBottomley@parallels.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
[ Make it also print the command name when warning - Linus ]
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Diff: diff --git a/block/scsi_ioctl.c b/block/scsi_ioctl.c
index a2c11f330872c..260fa80ef5750 100644
--- a/block/scsi_ioctl.c
+++ b/block/scsi_ioctl.c
@@ -22,10 +22,11 @@
 #include <linux/module.h>
 #include <linux/blkdev.h>
 #include <linux/capability.h>
 #include <linux/completion.h>
 #include <linux/cdrom.h>
+#include <linux/ratelimit.h>
 #include <linux/slab.h>
 #include <linux/times.h>
 #include <asm/uaccess.h>
 
 #include <scsi/scsi.h>
@@ -688,13 +689,57 @@ int scsi_cmd_ioctl(struct request_queue *q, struct gendisk *bd_disk, fmode_t mod
 
 	return err;
 }
 EXPORT_SYMBOL(scsi_cmd_ioctl);
 
+int scsi_verify_blk_ioctl(struct block_device *bd, unsigned int cmd)
+{
+	if (bd && bd == bd->bd_contains)
+		return 0;
+
+	/* Actually none of these is particularly useful on a partition,
+	 * but they are safe.
+	 */
+	switch (cmd) {
+	case SCSI_IOCTL_GET_IDLUN:
+	case SCSI_IOCTL_GET_BUS_NUMBER:
+	case SCSI_IOCTL_GET_PCI:
+	case SCSI_IOCTL_PROBE_HOST:
+	case SG_GET_VERSION_NUM:
+	case SG_SET_TIMEOUT:
+	case SG_GET_TIMEOUT:
+	case SG_GET_RESERVED_SIZE:
+	case SG_SET_RESERVED_SIZE:
+	case SG_EMULATED_HOST:
+		return 0;
+	case CDROM_GET_CAPABILITY:
+		/* Keep this until we remove the printk below.  udev sends it
+		 * and we do not want to spam dmesg about it.   CD-ROMs do
+		 * not have partitions, so we get here only for disks.
+		 */
+		return -ENOIOCTLCMD;
+	default:
+		break;
+	}
+
+	/* In particular, rule out all resets and host-specific ioctls.  */
+	printk_ratelimited(KERN_WARNING
+			   "%s: sending ioctl %x to a partition!\n", current->comm, cmd);
+
+	return capable(CAP_SYS_RAWIO) ? 0 : -ENOIOCTLCMD;
+}
+EXPORT_SYMBOL(scsi_verify_blk_ioctl);
+
 int scsi_cmd_blk_ioctl(struct block_device *bd, fmode_t mode,
 		       unsigned int cmd, void __user *arg)
 {
+	int ret;
+
+	ret = scsi_verify_blk_ioctl(bd, cmd);
+	if (ret < 0)
+		return ret;
+
 	return scsi_cmd_ioctl(bd->bd_disk->queue, bd->bd_disk, mode, cmd, arg);
 }
 EXPORT_SYMBOL(scsi_cmd_blk_ioctl);
 
 static int __init blk_scsi_ioctl_init(void)
diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
index b4d57bb04c725..c691fb50e6cbf 100644
--- a/drivers/scsi/sd.c
+++ b/drivers/scsi/sd.c
@@ -1073,10 +1073,14 @@ static int sd_ioctl(struct block_device *bdev, fmode_t mode,
 	int error;
     
 	SCSI_LOG_IOCTL(1, sd_printk(KERN_INFO, sdkp, "sd_ioctl: disk=%s, "
 				    "cmd=0x%x\n", disk->disk_name, cmd));
 
+	error = scsi_verify_blk_ioctl(bdev, cmd);
+	if (error < 0)
+		return error;
+
 	/*
 	 * If we are in the middle of error recovery, don't let anyone
 	 * else try and use this device.  Also, if error recovery fails, it
 	 * may try and take the device offline, in which case all further
 	 * access to the device is prohibited.
@@ -1265,10 +1269,15 @@ static void sd_rescan(struct device *dev)
  */
 static int sd_compat_ioctl(struct block_device *bdev, fmode_t mode,
 			   unsigned int cmd, unsigned long arg)
 {
 	struct scsi_device *sdev = scsi_disk(bdev->bd_disk)->device;
+	int ret;
+
+	ret = scsi_verify_blk_ioctl(bdev, cmd);
+	if (ret < 0)
+		return ret;
 
 	/*
 	 * If we are in the middle of error recovery, don't let anyone
 	 * else try and use this device.  Also, if error recovery fails, it
 	 * may try and take the device offline, in which case all further
@@ -1276,12 +1285,10 @@ static int sd_compat_ioctl(struct block_device *bdev, fmode_t mode,
 	 */
 	if (!scsi_block_when_processing_errors(sdev))
 		return -ENODEV;
 	       
 	if (sdev->host->hostt->compat_ioctl) {
-		int ret;
-
 		ret = sdev->host->hostt->compat_ioctl(sdev, cmd, (void __user *)arg);
 
 		return ret;
 	}
 
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index ca7b869508c7a..0ed1eb062313f 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -673,10 +673,11 @@ extern int blk_rq_prep_clone(struct request *rq, struct request *rq_src,
 extern void blk_rq_unprep_clone(struct request *rq);
 extern int blk_insert_cloned_request(struct request_queue *q,
 				     struct request *rq);
 extern void blk_delay_queue(struct request_queue *, unsigned long);
 extern void blk_recount_segments(struct request_queue *, struct bio *);
+extern int scsi_verify_blk_ioctl(struct block_device *, unsigned int);
 extern int scsi_cmd_blk_ioctl(struct block_device *, fmode_t,
 			      unsigned int, void __user *);
 extern int scsi_cmd_ioctl(struct request_queue *, struct gendisk *, fmode_t,
 			  unsigned int, void __user *);
 extern int sg_scsi_ioctl(struct request_queue *, struct gendisk *, fmode_t,

Vulnerable code: 		int ret;

Fixed code: #include <linux/ratelimit.h>
int scsi_verify_blk_ioctl(struct block_device *bd, unsigned int cmd)
{
	if (bd && bd == bd->bd_contains)
		return 0;

	/* Actually none of these is particularly useful on a partition,
	 * but they are safe.
	 */
	switch (cmd) {
	case SCSI_IOCTL_GET_IDLUN:
	case SCSI_IOCTL_GET_BUS_NUMBER:
	case SCSI_IOCTL_GET_PCI:
	case SCSI_IOCTL_PROBE_HOST:
	case SG_GET_VERSION_NUM:
	case SG_SET_TIMEOUT:
	case SG_GET_TIMEOUT:
	case SG_GET_RESERVED_SIZE:
	case SG_SET_RESERVED_SIZE:
	case SG_EMULATED_HOST:
		return 0;
	case CDROM_GET_CAPABILITY:
		/* Keep this until we remove the printk below.  udev sends it
		 * and we do not want to spam dmesg about it.   CD-ROMs do
		 * not have partitions, so we get here only for disks.
		 */
		return -ENOIOCTLCMD;
	default:
		break;
	}

	/* In particular, rule out all resets and host-specific ioctls.  */
	printk_ratelimited(KERN_WARNING
			   "%s: sending ioctl %x to a partition!\n", current->comm, cmd);

	return capable(CAP_SYS_RAWIO) ? 0 : -ENOIOCTLCMD;
}
EXPORT_SYMBOL(scsi_verify_blk_ioctl);

	int ret;

	ret = scsi_verify_blk_ioctl(bd, cmd);
	if (ret < 0)
		return ret;

	error = scsi_verify_blk_ioctl(bdev, cmd);
	if (error < 0)
		return error;

	int ret;

	ret = scsi_verify_blk_ioctl(bdev, cmd);
	if (ret < 0)
		return ret;
extern int scsi_verify_blk_ioctl(struct block_device *, unsigned int);