Date: Tue, 4 Nov 2008 10:45:29 -0600
From: "Serge E. Hallyn" <serue@us.ibm.com>
To: Eric Paris <eparis@redhat.com>
Cc: linux-kernel@vger.kernel.org, linux-audit@redhat.com, sgrubb@redhat.com,
       morgan@kernel.org, viro@ZenIV.linux.org.uk
Subject: Re: [PATCH -v2 1/4] CAPABILITIES: add cpu endian vfs caps structure
Message-ID: <20081104164529.GA24938@us.ibm.com>
References: <20081103201742.12059.36030.stgit@paris.rdu.redhat.com>
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Quoting Eric Paris (eparis@redhat.com):
> This patch add a generic cpu endian caps structure and externally available
> functions which retrieve fcaps information from disk.  This information is
> necessary so fcaps information can be collected and recorded by the audit
> system.
> 
> Signed-off-by: Eric Paris <eparis@redhat.com>

Looks good, and seems to make the code a bit easier to read as well.

Acked-by: Serge Hallyn <serue@us.ibm.com>

thanks,
-serge

> ---
> 
>  include/linux/capability.h |    7 ++
>  security/commoncap.c       |  129 ++++++++++++++++++++++++--------------------
>  2 files changed, 78 insertions(+), 58 deletions(-)
> 
> diff --git a/include/linux/capability.h b/include/linux/capability.h
> index 9d1fe30..9d64a9c 100644
> --- a/include/linux/capability.h
> +++ b/include/linux/capability.h
> @@ -96,6 +96,13 @@ typedef struct kernel_cap_struct {
>  	__u32 cap[_KERNEL_CAPABILITY_U32S];
>  } kernel_cap_t;
> 
> +/* exact same as vfs_cap_data but in cpu endian and always filled completely */
> +struct cpu_vfs_cap_data {
> +	__u32 magic_etc;
> +	kernel_cap_t permitted;
> +	kernel_cap_t inheritable;
> +};
> +
>  #define _USER_CAP_HEADER_SIZE  (sizeof(struct __user_cap_header_struct))
>  #define _KERNEL_CAP_T_SIZE     (sizeof(kernel_cap_t))
> 
> diff --git a/security/commoncap.c b/security/commoncap.c
> index 3976613..8bb95ed 100644
> --- a/security/commoncap.c
> +++ b/security/commoncap.c
> @@ -202,17 +202,70 @@ int cap_inode_killpriv(struct dentry *dentry)
>  	return inode->i_op->removexattr(dentry, XATTR_NAME_CAPS);
>  }
> 
> -static inline int cap_from_disk(struct vfs_cap_data *caps,
> -				struct linux_binprm *bprm, unsigned size)
> +static inline int bprm_caps_from_vfs_caps(struct cpu_vfs_cap_data *caps,
> +					  struct linux_binprm *bprm)
>  {
> +	unsigned i;
> +	int ret = 0;
> +
> +	if (caps->magic_etc & VFS_CAP_FLAGS_EFFECTIVE)
> +		bprm->cap_effective = true;
> +	else
> +		bprm->cap_effective = false;
> +
> +	CAP_FOR_EACH_U32(i) {
> +		__u32 permitted = caps->permitted.cap[i];
> +		__u32 inheritable = caps->inheritable.cap[i];
> +
> +		/*
> +		 * pP' = (X & fP) | (pI & fI)
> +		 */
> +		bprm->cap_post_exec_permitted.cap[i] =
> +			(current->cap_bset.cap[i] & permitted) |
> +			(current->cap_inheritable.cap[i] & inheritable);
> +
> +		if (permitted & ~bprm->cap_post_exec_permitted.cap[i]) {
> +			/*
> +			 * insufficient to execute correctly
> +			 */
> +			ret = -EPERM;
> +		}
> +	}
> +
> +	/*
> +	 * For legacy apps, with no internal support for recognizing they
> +	 * do not have enough capabilities, we return an error if they are
> +	 * missing some "forced" (aka file-permitted) capabilities.
> +	 */
> +	return bprm->cap_effective ? ret : 0;
> +}
> +
> +int get_vfs_caps_from_disk(const struct dentry *dentry, struct cpu_vfs_cap_data *cpu_caps)
> +{
> +	struct inode *inode = dentry->d_inode;
>  	__u32 magic_etc;
>  	unsigned tocopy, i;
> -	int ret;
> +	int size;
> +	struct vfs_cap_data caps;
> +
> +	memset(cpu_caps, 0, sizeof(struct cpu_vfs_cap_data));
> +
> +	if (!inode || !inode->i_op || !inode->i_op->getxattr)
> +		return -ENODATA;
> +
> +	size = inode->i_op->getxattr((struct dentry *)dentry, XATTR_NAME_CAPS, &caps,
> +				   XATTR_CAPS_SZ);
> +	if (size == -ENODATA || size == -EOPNOTSUPP) {
> +		/* no data, that's ok */
> +		return -ENODATA;
> +	}
> +	if (size < 0)
> +		return size;
> 
>  	if (size < sizeof(magic_etc))
>  		return -EINVAL;
> 
> -	magic_etc = le32_to_cpu(caps->magic_etc);
> +	cpu_caps->magic_etc = magic_etc = le32_to_cpu(caps.magic_etc);
> 
>  	switch ((magic_etc & VFS_CAP_REVISION_MASK)) {
>  	case VFS_CAP_REVISION_1:
> @@ -229,46 +282,13 @@ static inline int cap_from_disk(struct vfs_cap_data *caps,
>  		return -EINVAL;
>  	}
> 
> -	if (magic_etc & VFS_CAP_FLAGS_EFFECTIVE) {
> -		bprm->cap_effective = true;
> -	} else {
> -		bprm->cap_effective = false;
> -	}
> -
> -	ret = 0;
> -
>  	CAP_FOR_EACH_U32(i) {
> -		__u32 value_cpu;
> -
> -		if (i >= tocopy) {
> -			/*
> -			 * Legacy capability sets have no upper bits
> -			 */
> -			bprm->cap_post_exec_permitted.cap[i] = 0;
> -			continue;
> -		}
> -		/*
> -		 * pP' = (X & fP) | (pI & fI)
> -		 */
> -		value_cpu = le32_to_cpu(caps->data[i].permitted);
> -		bprm->cap_post_exec_permitted.cap[i] =
> -			(current->cap_bset.cap[i] & value_cpu) |
> -			(current->cap_inheritable.cap[i] &
> -				le32_to_cpu(caps->data[i].inheritable));
> -		if (value_cpu & ~bprm->cap_post_exec_permitted.cap[i]) {
> -			/*
> -			 * insufficient to execute correctly
> -			 */
> -			ret = -EPERM;
> -		}
> +		if (i >= tocopy)
> +			break;
> +		cpu_caps->permitted.cap[i] = le32_to_cpu(caps.data[i].permitted);
> +		cpu_caps->inheritable.cap[i] = le32_to_cpu(caps.data[i].inheritable);
>  	}
> -
> -	/*
> -	 * For legacy apps, with no internal support for recognizing they
> -	 * do not have enough capabilities, we return an error if they are
> -	 * missing some "forced" (aka file-permitted) capabilities.
> -	 */
> -	return bprm->cap_effective ? ret : 0;
> +	return 0;
>  }
> 
>  /* Locate any VFS capabilities: */
> @@ -276,8 +296,7 @@ static int get_file_caps(struct linux_binprm *bprm)
>  {
>  	struct dentry *dentry;
>  	int rc = 0;
> -	struct vfs_cap_data vcaps;
> -	struct inode *inode;
> +	struct cpu_vfs_cap_data vcaps;
> 
>  	bprm_clear_caps(bprm);
> 
> @@ -285,24 +304,18 @@ static int get_file_caps(struct linux_binprm *bprm)
>  		return 0;
> 
>  	dentry = dget(bprm->file->f_dentry);
> -	inode = dentry->d_inode;
> -	if (!inode->i_op || !inode->i_op->getxattr)
> -		goto out;
> 
> -	rc = inode->i_op->getxattr(dentry, XATTR_NAME_CAPS, &vcaps,
> -				   XATTR_CAPS_SZ);
> -	if (rc == -ENODATA || rc == -EOPNOTSUPP) {
> -		/* no data, that's ok */
> -		rc = 0;
> +	rc = get_vfs_caps_from_disk(dentry, &vcaps);
> +	if (rc < 0) {
> +		if (rc == -EINVAL)
> +			printk(KERN_NOTICE "%s: get_vfs_caps_from_disk returned %d for %s\n",
> +				__func__, rc, bprm->filename);
> +		else if (rc == -ENODATA)
> +			rc = 0;
>  		goto out;
>  	}
> -	if (rc < 0)
> -		goto out;
> 
> -	rc = cap_from_disk(&vcaps, bprm, rc);
> -	if (rc == -EINVAL)
> -		printk(KERN_NOTICE "%s: cap_from_disk returned %d for %s\n",
> -		       __func__, rc, bprm->filename);
> +	rc = bprm_caps_from_vfs_caps(&vcaps, bprm);
> 
>  out:
>  	dput(dentry);
--
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