block: fail SCSI passthrough ioctls on partition devices

PATCH In review Paolo Bonzini 2 participants 2 messages Jan 27, 2012 1 message not in the archive

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Paolo Bonzini

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2012-01-27 16:56 UTC #1 lore raw

PATCH 1/1 block: fail SCSI passthrough ioctls on partition devices

In reply to a message not in the archive

commit 0bfc96cb77224736dfa35c3c555d37b3646ef35e upstream.

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 [email protected]

Cc Jens Axboe <[email protected]>

Cc James Bottomley <[email protected]>

Signed-off-by Paolo Bonzini <[email protected]>

[ Make it also print the command name when warning - Linus ]

Signed-off-by Linus Torvalds <[email protected]>

[ Changes with respect to 3.3: return -ENOTTY from scsi_verify_blk_ioctl
and -ENOIOCTLCMD from sd_compat_ioctl. ]

---
 block/scsi_ioctl.c     |   45 +++++++++++++++++++++++++++++++++++++++++++++
 drivers/scsi/sd.c      |   11 +++++++++--
 include/linux/blkdev.h |    1 +
 3 files changed, 55 insertions(+), 2 deletions(-)

block/scsi_ioctl.c +45 -0

@@ -24,6 +24,7 @@
 #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>

@@ -689,9 +690,53 @@ int scsi_cmd_ioctl(struct request_queue
 }
 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 -ENOTTY;
+	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 : -ENOTTY;
+}
+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);

drivers/scsi/sd.c +9 -2

@@ -817,6 +817,10 @@ static int sd_ioctl(struct block_device
 	SCSI_LOG_IOCTL(1, printk("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

@@ -996,6 +1000,11 @@ static int sd_compat_ioctl(struct block_
 			   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 -ENOIOCTLCMD;
 
 	/*
 	 * If we are in the middle of error recovery, don't let anyone

@@ -1007,8 +1016,6 @@ static int sd_compat_ioctl(struct block_
 		return -ENODEV;
 	       
 	if (sdev->host->hostt->compat_ioctl) {
-		int ret;
-
 		ret = sdev->host->hostt->compat_ioctl(sdev, cmd, (void __user *)arg);
 
 		return ret;

include/linux/blkdev.h +1 -0

@@ -777,6 +777,7 @@ extern void blk_plug_device(struct reque
 extern void blk_plug_device_unlocked(struct request_queue *);
 extern int blk_remove_plug(struct request_queue *);
 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,

Greg KH

2012-01-27 23:23 UTC #2 lore raw

Quoted 34 lines · Paolo Bonzini

commit 0bfc96cb77224736dfa35c3c555d37b3646ef35e upstream.
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 [email protected]
Cc Jens Axboe <[email protected]>
Cc James Bottomley <[email protected]>
Signed-off-by Paolo Bonzini <[email protected]>
[ Make it also print the command name when warning - Linus ]
Signed-off-by Linus Torvalds <[email protected]>

Quoted 2 lines

[ Changes with respect to 3.3: return -ENOTTY from scsi_verify_blk_ioctl
and -ENOIOCTLCMD from sd_compat_ioctl. ]

Thanks, I've replaced the version in the 2.6.32-stable queue with this one.

greg k-h