Re: [PATCH 04/26] KEYS: Add keyctl function to get a security label

[Stephen Smalley]

On Tue, 2008-01-15 at 23:47 +0000, David Howells wrote:
> Add a keyctl() function to get the security label of a key.
> 
> The following is added to Documentation/keys.txt:
> 
>  (*) Get the LSM security context attached to a key.
> 
> 	long keyctl(KEYCTL_GET_SECURITY, key_serial_t key, char *buffer,
> 		    size_t buflen)
> 
>      This function returns a string that represents the LSM security context
>      attached to a key in the buffer provided.
> 
>      Unless there's an error, it always returns the amount of data it could
>      produce, even if that's too big for the buffer, but it won't copy more
>      than requested to userspace. If the buffer pointer is NULL then no copy
>      will take place.
> 
>      A NUL character is included at the end of the string if the buffer is
>      sufficiently big.  This is included in the returned count.  If no LSM is
>      in force then an empty string will be returned.
> 
>      A process must have view permission on the key for this function to be
>      successful.
> 
> Signed-off-by: David Howells <dhowells@xxxxxxxxxx>

Acked-by:  Stephen Smalley <sds@xxxxxxxxxxxxx>

You can push that one up anytime.

> ---
> 
>  Documentation/keys.txt   |   21 +++++++++++++++
>  include/linux/keyctl.h   |    1 +
>  include/linux/security.h |   20 +++++++++++++-
>  security/dummy.c         |    8 ++++++
>  security/keys/compat.c   |    3 ++
>  security/keys/keyctl.c   |   66 ++++++++++++++++++++++++++++++++++++++++++++++
>  security/security.c      |    5 +++
>  security/selinux/hooks.c |   21 +++++++++++++--
>  8 files changed, 141 insertions(+), 4 deletions(-)
> 
> 
> diff --git a/Documentation/keys.txt b/Documentation/keys.txt
> index b82d38d..be424b0 100644
> --- a/Documentation/keys.txt
> +++ b/Documentation/keys.txt
> @@ -711,6 +711,27 @@ The keyctl syscall functions are:
>       The assumed authoritative key is inherited across fork and exec.
>  
> 
> + (*) Get the LSM security context attached to a key.
> +
> +	long keyctl(KEYCTL_GET_SECURITY, key_serial_t key, char *buffer,
> +		    size_t buflen)
> +
> +     This function returns a string that represents the LSM security context
> +     attached to a key in the buffer provided.
> +
> +     Unless there's an error, it always returns the amount of data it could
> +     produce, even if that's too big for the buffer, but it won't copy more
> +     than requested to userspace. If the buffer pointer is NULL then no copy
> +     will take place.
> +
> +     A NUL character is included at the end of the string if the buffer is
> +     sufficiently big.  This is included in the returned count.  If no LSM is
> +     in force then an empty string will be returned.
> +
> +     A process must have view permission on the key for this function to be
> +     successful.
> +
> +
>  ===============
>  KERNEL SERVICES
>  ===============
> diff --git a/include/linux/keyctl.h b/include/linux/keyctl.h
> index 3365945..656ee6b 100644
> --- a/include/linux/keyctl.h
> +++ b/include/linux/keyctl.h
> @@ -49,5 +49,6 @@
>  #define KEYCTL_SET_REQKEY_KEYRING	14	/* set default request-key keyring */
>  #define KEYCTL_SET_TIMEOUT		15	/* set key timeout */
>  #define KEYCTL_ASSUME_AUTHORITY		16	/* assume request_key() authorisation */
> +#define KEYCTL_GET_SECURITY		17	/* get key security label */
>  
>  #endif /*  _LINUX_KEYCTL_H */
> diff --git a/include/linux/security.h b/include/linux/security.h
> index ac05083..8d9e946 100644
> --- a/include/linux/security.h
> +++ b/include/linux/security.h
> @@ -959,6 +959,17 @@ struct request_sock;
>   *	@perm describes the combination of permissions required of this key.
>   *	Return 1 if permission granted, 0 if permission denied and -ve it the
>   *      normal permissions model should be effected.
> + * @key_getsecurity:
> + *	Get a textual representation of the security context attached to a key
> + *	for the purposes of honouring KEYCTL_GETSECURITY.  This function
> + *	allocates the storage for the NUL-terminated string and the caller
> + *	should free it.
> + *	@key points to the key to be queried.
> + *	@_buffer points to a pointer that should be set to point to the
> + *	 resulting string (if no label or an error occurs).
> + *	Return the length of the string (including terminating NUL) or -ve if
> + *      an error.
> + *	May also return 0 (and a NULL buffer pointer) if there is no label.
>   *
>   * Security hooks affecting all System V IPC operations.
>   *
> @@ -1437,7 +1448,7 @@ struct security_operations {
>  	int (*key_permission)(key_ref_t key_ref,
>  			      struct task_struct *context,
>  			      key_perm_t perm);
> -
> +	int (*key_getsecurity)(struct key *key, char **_buffer);
>  #endif	/* CONFIG_KEYS */
>  
>  };
> @@ -2567,6 +2578,7 @@ int security_key_alloc(struct key *key, struct task_struct *tsk, unsigned long f
>  void security_key_free(struct key *key);
>  int security_key_permission(key_ref_t key_ref,
>  			    struct task_struct *context, key_perm_t perm);
> +int security_key_getsecurity(struct key *key, char **_buffer);
>  
>  #else
>  
> @@ -2588,6 +2600,12 @@ static inline int security_key_permission(key_ref_t key_ref,
>  	return 0;
>  }
>  
> +static inline int security_key_getsecurity(struct key *key, char **_buffer)
> +{
> +	*_buffer = NULL;
> +	return 0;
> +}
> +
>  #endif
>  #endif /* CONFIG_KEYS */
>  
> diff --git a/security/dummy.c b/security/dummy.c
> index 3ccfbbe..0e7f35c 100644
> --- a/security/dummy.c
> +++ b/security/dummy.c
> @@ -949,6 +949,13 @@ static inline int dummy_key_permission(key_ref_t key_ref,
>  {
>  	return 0;
>  }
> +
> +static int dummy_key_getsecurity(struct key *key, char **_buffer)
> +{
> +	*_buffer = NULL;
> +	return 0;
> +}
> +
>  #endif /* CONFIG_KEYS */
>  
>  struct security_operations dummy_security_ops;
> @@ -1133,6 +1140,7 @@ void security_fixup_ops (struct security_operations *ops)
>  	set_to_dummy_if_null(ops, key_alloc);
>  	set_to_dummy_if_null(ops, key_free);
>  	set_to_dummy_if_null(ops, key_permission);
> +	set_to_dummy_if_null(ops, key_getsecurity);
>  #endif	/* CONFIG_KEYS */
>  
>  }
> diff --git a/security/keys/compat.c b/security/keys/compat.c
> index e10ec99..c766c68 100644
> --- a/security/keys/compat.c
> +++ b/security/keys/compat.c
> @@ -79,6 +79,9 @@ asmlinkage long compat_sys_keyctl(u32 option,
>  	case KEYCTL_ASSUME_AUTHORITY:
>  		return keyctl_assume_authority(arg2);
>  
> +	case KEYCTL_GET_SECURITY:
> +		return keyctl_get_security(arg2, compat_ptr(arg3), arg4);
> +
>  	default:
>  		return -EOPNOTSUPP;
>  	}
> diff --git a/security/keys/keyctl.c b/security/keys/keyctl.c
> index 1698bf9..56e963b 100644
> --- a/security/keys/keyctl.c
> +++ b/security/keys/keyctl.c
> @@ -20,6 +20,7 @@
>  #include <linux/string.h>
>  #include <linux/err.h>
>  #include <linux/vmalloc.h>
> +#include <linux/security.h>
>  #include <asm/uaccess.h>
>  #include "internal.h"
>  
> @@ -1080,6 +1081,66 @@ error:
>  
>  } /* end keyctl_assume_authority() */
>  
> +/*
> + * get the security label of a key
> + * - the key must grant us view permission
> + * - if there's a buffer, we place up to buflen bytes of data into it
> + * - unless there's an error, we return the amount of information available,
> + *   irrespective of how much we may have copied (including the terminal NUL)
> + * - implements keyctl(KEYCTL_GET_SECURITY)
> + */
> +long keyctl_get_security(key_serial_t keyid,
> +			 char __user *buffer,
> +			 size_t buflen)
> +{
> +	struct key *key, *instkey;
> +	key_ref_t key_ref;
> +	char *context;
> +	long ret;
> +
> +	key_ref = lookup_user_key(NULL, keyid, 0, 1, KEY_VIEW);
> +	if (IS_ERR(key_ref)) {
> +		if (PTR_ERR(key_ref) != -EACCES)
> +			return PTR_ERR(key_ref);
> +
> +		/* viewing a key under construction is also permitted if we
> +		 * have the authorisation token handy */
> +		instkey = key_get_instantiation_authkey(keyid);
> +		if (IS_ERR(instkey))
> +			return PTR_ERR(key_ref);
> +		key_put(instkey);
> +
> +		key_ref = lookup_user_key(NULL, keyid, 0, 1, 0);
> +		if (IS_ERR(key_ref))
> +			return PTR_ERR(key_ref);
> +	}
> +
> +	key = key_ref_to_ptr(key_ref);
> +	ret = security_key_getsecurity(key, &context);
> +	if (ret == 0) {
> +		/* if no information was returned, give userspace an empty
> +		 * string */
> +		ret = 1;
> +		if (buffer && buflen > 0 &&
> +		    copy_to_user(buffer, "", 1) != 0)
> +			ret = -EFAULT;
> +	} else if (ret > 0) {
> +		/* return as much data as there's room for */
> +		if (buffer && buflen > 0) {
> +			if (buflen > ret)
> +				buflen = ret;
> +
> +			if (copy_to_user(buffer, context, buflen) != 0)
> +				ret = -EFAULT;
> +		}
> +
> +		kfree(context);
> +	}
> +
> +	key_ref_put(key_ref);
> +	return ret;
> +}
> +
>  /*****************************************************************************/
>  /*
>   * the key control system call
> @@ -1160,6 +1221,11 @@ asmlinkage long sys_keyctl(int option, unsigned long arg2, unsigned long arg3,
>  	case KEYCTL_ASSUME_AUTHORITY:
>  		return keyctl_assume_authority((key_serial_t) arg2);
>  
> +	case KEYCTL_GET_SECURITY:
> +		return keyctl_get_security((key_serial_t) arg2,
> +					   (char *) arg3,
> +					   (size_t) arg4);
> +
>  	default:
>  		return -EOPNOTSUPP;
>  	}
> diff --git a/security/security.c b/security/security.c
> index 0e1f1f1..16213e3 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -1079,4 +1079,9 @@ int security_key_permission(key_ref_t key_ref,
>  	return security_ops->key_permission(key_ref, context, perm);
>  }
>  
> +int security_key_getsecurity(struct key *key, char **_buffer)
> +{
> +	return security_ops->key_getsecurity(key, _buffer);
> +}
> +
>  #endif	/* CONFIG_KEYS */
> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> index 9f3124b..bd4cfab 100644
> --- a/security/selinux/hooks.c
> +++ b/security/selinux/hooks.c
> @@ -4768,6 +4768,20 @@ static int selinux_key_permission(key_ref_t key_ref,
>  			    SECCLASS_KEY, perm, NULL);
>  }
>  
> +static int selinux_key_getsecurity(struct key *key, char **_buffer)
> +{
> +	struct key_security_struct *ksec = key->security;
> +	char *context = NULL;
> +	unsigned len;
> +	int rc;
> +
> +	rc = security_sid_to_context(ksec->sid, &context, &len);
> +	if (!rc)
> +		rc = len;
> +	*_buffer = context;
> +	return rc;
> +}
> +
>  #endif
>  
>  static struct security_operations selinux_ops = {
> @@ -4943,9 +4957,10 @@ static struct security_operations selinux_ops = {
>  #endif
>  
>  #ifdef CONFIG_KEYS
> -	.key_alloc =                    selinux_key_alloc,
> -	.key_free =                     selinux_key_free,
> -	.key_permission =               selinux_key_permission,
> +	.key_alloc =			selinux_key_alloc,
> +	.key_free =			selinux_key_free,
> +	.key_permission =		selinux_key_permission,
> +	.key_getsecurity =		selinux_key_getsecurity,
>  #endif
>  };
>  
-- 
Stephen Smalley
National Security Agency

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