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Message-ID: <474B8D8B.3000008@kernel.org>
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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