selinux: implement the security_uring_cmd() LSM hook

Add a SELinux access control for the iouring IORING_OP_URING_CMD
command.  This includes the addition of a new permission in the
existing "io_uring" object class: "cmd".  The subject of the new
permission check is the domain of the process requesting access, the
object is the open file which points to the device/file that is the
target of the IORING_OP_URING_CMD operation.  A sample policy rule
is shown below:

  allow <domain> <file>:io_uring { cmd };

Cc: stable@vger.kernel.org
Fixes: ee692a2 ("fs,io_uring: add infrastructure for uring-cmd")
Signed-off-by: Paul Moore <paul@paul-moore.com>

security/selinux/hooks.c

@@ -91,6 +91,7 @@
 #include <uapi/linux/mount.h>
 #include <linux/fsnotify.h>
 #include <linux/fanotify.h>
+#include <linux/io_uring.h>
 
 #include "avc.h"
 #include "objsec.h"
@@ -6987,6 +6988,28 @@ static int selinux_uring_sqpoll(void)
 	return avc_has_perm(&selinux_state, sid, sid,
 			    SECCLASS_IO_URING, IO_URING__SQPOLL, NULL);
 }
+
+/**
+ * selinux_uring_cmd - check if IORING_OP_URING_CMD is allowed
+ * @ioucmd: the io_uring command structure
+ *
+ * Check to see if the current domain is allowed to execute an
+ * IORING_OP_URING_CMD against the device/file specified in @ioucmd.
+ *
+ */
+static int selinux_uring_cmd(struct io_uring_cmd *ioucmd)
+{
+	struct file *file = ioucmd->file;
+	struct inode *inode = file_inode(file);
+	struct inode_security_struct *isec = selinux_inode(inode);
+	struct common_audit_data ad;
+
+	ad.type = LSM_AUDIT_DATA_FILE;
+	ad.u.file = file;
+
+	return avc_has_perm(&selinux_state, current_sid(), isec->sid,
+			    SECCLASS_IO_URING, IO_URING__CMD, &ad);
+}
 #endif /* CONFIG_IO_URING */
 
 /*
@@ -7231,6 +7254,7 @@ static struct security_hook_list selinux_hooks[] __lsm_ro_after_init = {
 #ifdef CONFIG_IO_URING
 	LSM_HOOK_INIT(uring_override_creds, selinux_uring_override_creds),
 	LSM_HOOK_INIT(uring_sqpoll, selinux_uring_sqpoll),
+	LSM_HOOK_INIT(uring_cmd, selinux_uring_cmd),
 #endif
 
 	/*

security/selinux/include/classmap.h

@@ -253,7 +253,7 @@ const struct security_class_mapping secclass_map[] = {
 	{ "anon_inode",
 	  { COMMON_FILE_PERMS, NULL } },
 	{ "io_uring",
-	  { "override_creds", "sqpoll", NULL } },
+	  { "override_creds", "sqpoll", "cmd", NULL } },
 	{ NULL }
   };