[PATCH for-next 1/2] nvme: add the permission-policy for command control

[Kanchan Joshi]

If CAP_SYS_ADMIN is present, nothing else is checked as before.
Otherwise takes the decision to allow the command based on following
rules:
- any admin-cmd is not allowed
- vendor-specific and fabric commmand are not allowed
- io-commands that can write are allowed if matching FMODE_WRITE
permission is present
- io-commands that read are allowed

Add a helper nvme_cmd_allowed that implements above policy. This is a prep
patch.

Signed-off-by: Kanchan Joshi <joshi.k at samsung.com>
---
 drivers/nvme/host/ioctl.c | 19 +++++++++++++++++++
 include/linux/nvme.h      |  1 +
 2 files changed, 20 insertions(+)

diff --git a/drivers/nvme/host/ioctl.c b/drivers/nvme/host/ioctl.c
index 548aca8b5b9f..6ca6477dd899 100644
--- a/drivers/nvme/host/ioctl.c
+++ b/drivers/nvme/host/ioctl.c
@@ -20,6 +20,25 @@ static void __user *nvme_to_user_ptr(uintptr_t ptrval)
 	return (void __user *)ptrval;
 }
 
+bool nvme_cmd_allowed(struct nvme_ns *ns, u8 opcode, fmode_t mode)
+{
+	/* root can do anything */
+	if (capable(CAP_SYS_ADMIN))
+		return true;
+	/* admin commands are not allowed */
+	if (ns == NULL)
+		return false;
+	/* exclude vendor-specific io and fabrics commands */
+	if (opcode >= nvme_cmd_vendor_start ||
+			opcode== nvme_fabrics_command)
+		return false;
+	/* allow write cmds only if matching FMODE is present */
+	if (opcode & 1)
+		return mode & FMODE_WRITE;
+	/* allow read cmds */
+	return true;
+}
+
 static void *nvme_add_user_metadata(struct bio *bio, void __user *ubuf,
 		unsigned len, u32 seed, bool write)
 {
diff --git a/include/linux/nvme.h b/include/linux/nvme.h
index ae53d74f3696..8396eb7ecb68 100644
--- a/include/linux/nvme.h
+++ b/include/linux/nvme.h
@@ -797,6 +797,7 @@ enum nvme_opcode {
 	nvme_cmd_zone_mgmt_send	= 0x79,
 	nvme_cmd_zone_mgmt_recv	= 0x7a,
 	nvme_cmd_zone_append	= 0x7d,
+	nvme_cmd_vendor_start	= 0x80,
 };
 
 #define nvme_opcode_name(opcode)	{ opcode, #opcode }
-- 
2.25.1