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Date:	Mon, 26 Nov 2007 19:22:51 -0800
From:	Andrew Morgan <morgan@...nel.org>
To:	casey@...aufler-ca.com
CC:	akpm@...l.org, torvalds@...l.org, linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org
Subject: Re: [PATCH] -mm (2.4.26-rc3-mm1) v2  Smack using capabilities 32
 and 33

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Signed-off-by: Andrew G. Morgan <morgan@...nel.org>

Cheers

Andrew

Casey Schaufler wrote:
> From: Casey Schaufler <casey@...aufler-ca.com>
> 
> This patch takes advantage of the increase in capability bits
> to allocate capabilities for Mandatory Access Control. Whereas
> Smack was overloading a previously allocated capability it is
> now using a pair, one for overriding access control checks and
> the other for changes to the MAC configuration.
> 
> The two capabilities allocated should be obvious in their intent.
> The comments in capability.h are intended to make it clear that
> there is no intention that implementations of MAC LSM modules
> be any more constrained by the presence of these capabilities
> than an implementation of DAC LSM modules are by the analogous
> DAC capabilities.
> 
> 
> Signed-off-by: Casey Schaufler <casey@...aufler-ca.com>
> 
> ---
> 
> The companion patch for libcap-2.02 is provided as an attachment.
> The attachment is not a kernel patch, although it would be easy to
> mistake it for one.
> 
> Introduces CAP_FS_MASK_B1 and uses it as appropriate. I think that
> I found all the places it needs to be used, but don't hesitate to
> let me know if I missed something.
> 
> Thank you.
> 
>  include/linux/capability.h |   24 ++++++++++++++++++++++--
>  security/smack/smack.h     |    8 --------
>  security/smack/smack_lsm.c |    8 ++++----
>  security/smack/smackfs.c   |   12 ++++++------
>  4 files changed, 32 insertions(+), 20 deletions(-)
> 
> diff -uprN -X linux-2.6.24-rc3-mm1-base/Documentation/dontdiff linux-2.6.24-rc3-mm1-base/include/linux/capability.h linux-2.6.24-rc3-mm1-smack/include/linux/capability.h
> --- linux-2.6.24-rc3-mm1-base/include/linux/capability.h	2007-11-22 01:51:36.000000000 -0800
> +++ linux-2.6.24-rc3-mm1-smack/include/linux/capability.h	2007-11-25 21:38:34.000000000 -0800
> @@ -314,6 +314,23 @@ typedef struct kernel_cap_struct {
>  
>  #define CAP_SETFCAP	     31
>  
> +/* Override MAC access.
> +   The base kernel enforces no MAC policy.
> +   An LSM may enforce a MAC policy, and if it does and it chooses
> +   to implement capability based overrides of that policy, this is
> +   the capability it should use to do so. */
> +
> +#define CAP_MAC_OVERRIDE     32
> +
> +/* Allow MAC configuration or state changes.
> +   The base kernel requires no MAC configuration.
> +   An LSM may enforce a MAC policy, and if it does and it chooses
> +   to implement capability based checks on modifications to that
> +   policy or the data required to maintain it, this is the
> +   capability it should use to do so. */
> +
> +#define CAP_MAC_ADMIN        33
> +
>  /*
>   * Bit location of each capability (used by user-space library and kernel)
>   */
> @@ -336,6 +353,8 @@ typedef struct kernel_cap_struct {
>  			    | CAP_TO_MASK(CAP_FOWNER)		\
>  			    | CAP_TO_MASK(CAP_FSETID))
>  
> +# define CAP_FS_MASK_B1     (CAP_TO_MASK(CAP_MAC_OVERRIDE))
> +
>  #if _LINUX_CAPABILITY_U32S != 2
>  # error Fix up hand-coded capability macro initializers
>  #else /* HAND-CODED capability initializers */
> @@ -343,8 +362,9 @@ typedef struct kernel_cap_struct {
>  # define CAP_EMPTY_SET    {{ 0, 0 }}
>  # define CAP_FULL_SET     {{ ~0, ~0 }}
>  # define CAP_INIT_EFF_SET {{ ~CAP_TO_MASK(CAP_SETPCAP), ~0 }}
> -# define CAP_FS_SET       {{ CAP_FS_MASK_B0, 0 }}
> -# define CAP_NFSD_SET     {{ CAP_FS_MASK_B0|CAP_TO_MASK(CAP_SYS_RESOURCE), 0 }}
> +# define CAP_FS_SET       {{ CAP_FS_MASK_B0, CAP_FS_MASK_B1 } }
> +# define CAP_NFSD_SET     {{ CAP_FS_MASK_B0|CAP_TO_MASK(CAP_SYS_RESOURCE), \
> +			     CAP_FS_MASK_B1 } }
>  
>  #endif /* _LINUX_CAPABILITY_U32S != 2 */
>  
> diff -uprN -X linux-2.6.24-rc3-mm1-base/Documentation/dontdiff linux-2.6.24-rc3-mm1-base/security/smack/smackfs.c linux-2.6.24-rc3-mm1-smack/security/smack/smackfs.c
> --- linux-2.6.24-rc3-mm1-base/security/smack/smackfs.c	2007-11-22 01:51:43.000000000 -0800
> +++ linux-2.6.24-rc3-mm1-smack/security/smack/smackfs.c	2007-11-24 11:29:29.000000000 -0800
> @@ -241,7 +241,7 @@ static ssize_t smk_write_load(struct fil
>  	 * No partial writes.
>  	 * Enough data must be present.
>  	 */
> -	if (!capable(CAP_MAC_OVERRIDE))
> +	if (!capable(CAP_MAC_ADMIN))
>  		return -EPERM;
>  	if (*ppos != 0)
>  		return -EINVAL;
> @@ -474,7 +474,7 @@ static ssize_t smk_write_cipso(struct fi
>  	 * No partial writes.
>  	 * Enough data must be present.
>  	 */
> -	if (!capable(CAP_MAC_OVERRIDE))
> +	if (!capable(CAP_MAC_ADMIN))
>  		return -EPERM;
>  	if (*ppos != 0)
>  		return -EINVAL;
> @@ -601,7 +601,7 @@ static ssize_t smk_write_doi(struct file
>  	char temp[80];
>  	int i;
>  
> -	if (!capable(CAP_MAC_OVERRIDE))
> +	if (!capable(CAP_MAC_ADMIN))
>  		return -EPERM;
>  
>  	if (count >= sizeof(temp) || count == 0)
> @@ -666,7 +666,7 @@ static ssize_t smk_write_direct(struct f
>  	char temp[80];
>  	int i;
>  
> -	if (!capable(CAP_MAC_OVERRIDE))
> +	if (!capable(CAP_MAC_ADMIN))
>  		return -EPERM;
>  
>  	if (count >= sizeof(temp) || count == 0)
> @@ -747,7 +747,7 @@ static ssize_t smk_write_ambient(struct 
>  	char in[SMK_LABELLEN];
>  	char *smack;
>  
> -	if (!capable(CAP_MAC_OVERRIDE))
> +	if (!capable(CAP_MAC_ADMIN))
>  		return -EPERM;
>  
>  	if (count >= SMK_LABELLEN)
> @@ -840,7 +840,7 @@ static ssize_t smk_write_nltype(struct f
>  	char *cp;
>  	int i;
>  
> -	if (!capable(CAP_MAC_OVERRIDE))
> +	if (!capable(CAP_MAC_ADMIN))
>  		return -EPERM;
>  
>  	if (count >= 40)
> diff -uprN -X linux-2.6.24-rc3-mm1-base/Documentation/dontdiff linux-2.6.24-rc3-mm1-base/security/smack/smack.h linux-2.6.24-rc3-mm1-smack/security/smack/smack.h
> --- linux-2.6.24-rc3-mm1-base/security/smack/smack.h	2007-11-22 01:51:43.000000000 -0800
> +++ linux-2.6.24-rc3-mm1-smack/security/smack/smack.h	2007-11-22 03:03:19.000000000 -0800
> @@ -162,14 +162,6 @@ struct smack_known {
>  #define MAY_NOT		0
>  
>  /*
> - * There are not enough CAP bits available to make this
> - * real, so Casey borrowed the capability that looks to
> - * him like it has the best balance of similarity amd
> - * low use.
> - */
> -#define CAP_MAC_OVERRIDE CAP_LINUX_IMMUTABLE
> -
> -/*
>   * These functions are in smack_lsm.c
>   */
>  struct inode_smack *new_inode_smack(char *);
> diff -uprN -X linux-2.6.24-rc3-mm1-base/Documentation/dontdiff linux-2.6.24-rc3-mm1-base/security/smack/smack_lsm.c linux-2.6.24-rc3-mm1-smack/security/smack/smack_lsm.c
> --- linux-2.6.24-rc3-mm1-base/security/smack/smack_lsm.c	2007-11-22 01:51:43.000000000 -0800
> +++ linux-2.6.24-rc3-mm1-smack/security/smack/smack_lsm.c	2007-11-24 11:31:43.000000000 -0800
> @@ -585,7 +585,7 @@ static int smack_inode_setxattr(struct d
>  				void *value, size_t size, int flags)
>  {
>  	if (strcmp(name, XATTR_NAME_SMACK) == 0 &&
> -		!__capable(current, CAP_MAC_OVERRIDE))
> +		!__capable(current, CAP_MAC_ADMIN))
>  		return -EPERM;
>  
>  	return smk_curacc(smk_of_inode(dentry->d_inode), MAY_WRITE);
> @@ -649,14 +649,14 @@ static int smack_inode_getxattr(struct d
>   * @dentry: the object
>   * @name: name of the attribute
>   *
> - * Removing the Smack attribute requires CAP_MAC_OVERRIDE
> + * Removing the Smack attribute requires CAP_MAC_ADMIN
>   *
>   * Returns 0 if access is permitted, an error code otherwise
>   */
>  static int smack_inode_removexattr(struct dentry *dentry, char *name)
>  {
>  	if (strcmp(name, XATTR_NAME_SMACK) == 0 &&
> -		!__capable(current, CAP_MAC_OVERRIDE))
> +		!__capable(current, CAP_MAC_ADMIN))
>  		return -EPERM;
>  
>  	return smk_curacc(smk_of_inode(dentry->d_inode), MAY_WRITE);
> @@ -1956,7 +1956,7 @@ static int smack_setprocattr(struct task
>  {
>  	char *newsmack;
>  
> -	if (!__capable(p, CAP_MAC_OVERRIDE))
> +	if (!__capable(p, CAP_MAC_ADMIN))
>  		return -EPERM;
>  
>  	/*
> 
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