Re: [PATCH 3/3] sysfs: Add labeling support for sysfs

[Serge E. Hallyn]

Quoting David P. Quigley (dpquigl@xxxxxxxxxxxxx):
> This patch adds a setxattr handler to the file, directory, and symlink
> inode_operations structures for sysfs. The patch uses hooks introduced in the
> previous patch to handle the getting and setting of security information for
> the sysfs inodes. As was suggested by Eric Biederman the struct iattr in the
> sysfs_dirent structure has been replaced by a structure which contains the
> iattr, secdata and secdata length to allow the changes to persist in the event
> that the inode representing the sysfs_dirent is evicted. Because sysfs only
> stores this information when a change is made all the optional data is moved
> into one dynamically allocated field.
> 
> This patch addresses an issue where SELinux was denying virtd access to the PCI
> configuration entries in sysfs. The lack of setxattr handlers for sysfs
> required that a single label be assigned to all entries in sysfs. Granting virtd
> access to every entry in sysfs is not an acceptable solution so fine grained
> labeling of sysfs is required such that individual entries can be labeled
> appropriately.
> 
> Signed-off-by: David P. Quigley <dpquigl@xxxxxxxxxxxxx>

Hmm, all looks good to me...

Acked-by: Serge Hallyn <serue@xxxxxxxxxx>

> ---
>  fs/sysfs/dir.c           |    1 +
>  fs/sysfs/inode.c         |  135 +++++++++++++++++++++++++++++++++------------
>  fs/sysfs/symlink.c       |    2 +
>  fs/sysfs/sysfs.h         |   12 ++++-
>  security/selinux/hooks.c |    4 ++
>  5 files changed, 117 insertions(+), 37 deletions(-)
> 
> diff --git a/fs/sysfs/dir.c b/fs/sysfs/dir.c
> index 14f2d71..0050fc4 100644
> --- a/fs/sysfs/dir.c
> +++ b/fs/sysfs/dir.c
> @@ -760,6 +760,7 @@ static struct dentry * sysfs_lookup(struct inode *dir, struct dentry *dentry,
>  const struct inode_operations sysfs_dir_inode_operations = {
>  	.lookup		= sysfs_lookup,
>  	.setattr	= sysfs_setattr,
> +	.setxattr	= sysfs_setxattr,
>  };
> 
>  static void remove_dir(struct sysfs_dirent *sd)
> diff --git a/fs/sysfs/inode.c b/fs/sysfs/inode.c
> index 555f0ff..9889bf2 100644
> --- a/fs/sysfs/inode.c
> +++ b/fs/sysfs/inode.c
> @@ -18,6 +18,8 @@
>  #include <linux/capability.h>
>  #include <linux/errno.h>
>  #include <linux/sched.h>
> +#include <linux/xattr.h>
> +#include <linux/security.h>
>  #include "sysfs.h"
> 
>  extern struct super_block * sysfs_sb;
> @@ -35,6 +37,7 @@ static struct backing_dev_info sysfs_backing_dev_info = {
> 
>  static const struct inode_operations sysfs_inode_operations ={
>  	.setattr	= sysfs_setattr,
> +	.setxattr	= sysfs_setxattr,
>  };
> 
>  int __init sysfs_inode_init(void)
> @@ -42,18 +45,37 @@ int __init sysfs_inode_init(void)
>  	return bdi_init(&sysfs_backing_dev_info);
>  }
> 
> +struct sysfs_inode_attrs * sysfs_init_inode_attrs(struct sysfs_dirent * sd)
> +{
> +	struct sysfs_inode_attrs * attrs;
> +	struct iattr * iattrs;
> +
> +	attrs = kzalloc(sizeof(struct sysfs_inode_attrs), GFP_KERNEL);
> +	if(!attrs)
> +		return NULL;
> +	iattrs = &attrs->ia_iattr;
> +
> +	/* assign default attributes */
> +	iattrs->ia_mode = sd->s_mode;
> +	iattrs->ia_uid = 0;
> +	iattrs->ia_gid = 0;
> +	iattrs->ia_atime = iattrs->ia_mtime = iattrs->ia_ctime = CURRENT_TIME;
> +
> +	return attrs;
> +}
>  int sysfs_setattr(struct dentry * dentry, struct iattr * iattr)
>  {
>  	struct inode * inode = dentry->d_inode;
>  	struct sysfs_dirent * sd = dentry->d_fsdata;
> -	struct iattr * sd_iattr;
> +	struct sysfs_inode_attrs * sd_attrs;
> +	struct iattr * iattrs;
>  	unsigned int ia_valid = iattr->ia_valid;
>  	int error;
> 
>  	if (!sd)
>  		return -EINVAL;
> 
> -	sd_iattr = sd->s_iattr;
> +	sd_attrs = sd->s_iattr;
> 
>  	error = inode_change_ok(inode, iattr);
>  	if (error)
> @@ -65,42 +87,78 @@ int sysfs_setattr(struct dentry * dentry, struct iattr * iattr)
>  	if (error)
>  		return error;
> 
> -	if (!sd_iattr) {
> +	if (!sd_attrs) {
>  		/* setting attributes for the first time, allocate now */
> -		sd_iattr = kzalloc(sizeof(struct iattr), GFP_KERNEL);
> -		if (!sd_iattr)
> +		sd_attrs = sysfs_init_inode_attrs(sd);
> +		if (!sd_attrs)
>  			return -ENOMEM;
> -		/* assign default attributes */
> -		sd_iattr->ia_mode = sd->s_mode;
> -		sd_iattr->ia_uid = 0;
> -		sd_iattr->ia_gid = 0;
> -		sd_iattr->ia_atime = sd_iattr->ia_mtime = sd_iattr->ia_ctime = CURRENT_TIME;
> -		sd->s_iattr = sd_iattr;
> +		sd->s_iattr = sd_attrs;
> +	} else {
> +		/* attributes were changed atleast once in past */
> +		iattrs = &sd_attrs->ia_iattr;
> +
> +		if (ia_valid & ATTR_UID)
> +			iattrs->ia_uid = iattr->ia_uid;
> +		if (ia_valid & ATTR_GID)
> +			iattrs->ia_gid = iattr->ia_gid;
> +		if (ia_valid & ATTR_ATIME)
> +			iattrs->ia_atime = timespec_trunc(iattr->ia_atime,
> +					inode->i_sb->s_time_gran);
> +		if (ia_valid & ATTR_MTIME)
> +			iattrs->ia_mtime = timespec_trunc(iattr->ia_mtime,
> +					inode->i_sb->s_time_gran);
> +		if (ia_valid & ATTR_CTIME)
> +			iattrs->ia_ctime = timespec_trunc(iattr->ia_ctime,
> +					inode->i_sb->s_time_gran);
> +		if (ia_valid & ATTR_MODE) {
> +			umode_t mode = iattr->ia_mode;
> +
> +			if (!in_group_p(inode->i_gid) && !capable(CAP_FSETID))
> +				mode &= ~S_ISGID;
> +			iattrs->ia_mode = sd->s_mode = mode;
> +		}
>  	}
> +	return error;
> +}
> 
> -	/* attributes were changed atleast once in past */
> -
> -	if (ia_valid & ATTR_UID)
> -		sd_iattr->ia_uid = iattr->ia_uid;
> -	if (ia_valid & ATTR_GID)
> -		sd_iattr->ia_gid = iattr->ia_gid;
> -	if (ia_valid & ATTR_ATIME)
> -		sd_iattr->ia_atime = timespec_trunc(iattr->ia_atime,
> -						inode->i_sb->s_time_gran);
> -	if (ia_valid & ATTR_MTIME)
> -		sd_iattr->ia_mtime = timespec_trunc(iattr->ia_mtime,
> -						inode->i_sb->s_time_gran);
> -	if (ia_valid & ATTR_CTIME)
> -		sd_iattr->ia_ctime = timespec_trunc(iattr->ia_ctime,
> -						inode->i_sb->s_time_gran);
> -	if (ia_valid & ATTR_MODE) {
> -		umode_t mode = iattr->ia_mode;
> -
> -		if (!in_group_p(inode->i_gid) && !capable(CAP_FSETID))
> -			mode &= ~S_ISGID;
> -		sd_iattr->ia_mode = sd->s_mode = mode;
> -	}
> +int sysfs_setxattr(struct dentry *dentry, const char *name, const void *value,
> +		size_t size, int flags)
> +{
> +	struct sysfs_dirent *sd = dentry->d_fsdata;
> +	struct sysfs_inode_attrs *iattrs;
> +	char *suffix;
> +	char *secdata;
> +	int error;
> +	u32 secdata_len = 0;
> +
> +	if (!sd)
> +		return -EINVAL;
> +	if (!sd->s_iattr)
> +		sd->s_iattr = sysfs_init_inode_attrs(sd);
> +	if (!sd->s_iattr)
> +		return -ENOMEM;
> +
> +	iattrs = sd->s_iattr;
> +
> +	if (!strncmp(name, XATTR_SECURITY_PREFIX, XATTR_SECURITY_PREFIX_LEN)) {
> +		const char *suffix = name + XATTR_SECURITY_PREFIX_LEN;
> +		error = security_inode_setsecurity(dentry->d_inode, suffix,
> +						value, size, flags);
> +		if (error)
> +			goto out;
> +		error = security_inode_getsecctx(dentry->d_inode,
> +						&secdata, &secdata_len);
> +		if (error)
> +			goto out;
> +		if(iattrs->ia_secdata)
> +			security_release_secctx(iattrs->ia_secdata,
> +						iattrs->ia_secdata_len);
> +		iattrs->ia_secdata = secdata;
> +		iattrs->ia_secdata_len = secdata_len;
> 
> +	} else
> +		return -EINVAL;
> +out:
>  	return error;
>  }
> 
> @@ -146,6 +204,7 @@ static int sysfs_count_nlink(struct sysfs_dirent *sd)
>  static void sysfs_init_inode(struct sysfs_dirent *sd, struct inode *inode)
>  {
>  	struct bin_attribute *bin_attr;
> +	struct sysfs_inode_attrs * iattrs;
> 
>  	inode->i_private = sysfs_get(sd);
>  	inode->i_mapping->a_ops = &sysfs_aops;
> @@ -154,16 +213,20 @@ static void sysfs_init_inode(struct sysfs_dirent *sd, struct inode *inode)
>  	inode->i_ino = sd->s_ino;
>  	lockdep_set_class(&inode->i_mutex, &sysfs_inode_imutex_key);
> 
> -	if (sd->s_iattr) {
> +	iattrs = sd->s_iattr;
> +	if (iattrs) {
>  		/* sysfs_dirent has non-default attributes
>  		 * get them for the new inode from persistent copy
>  		 * in sysfs_dirent
>  		 */
> -		set_inode_attr(inode, sd->s_iattr);
> +		set_inode_attr(inode, &iattrs->ia_iattr);
> +		if (iattrs->ia_secdata)
> +			security_inode_notifysecctx(inode,
> +						iattrs->ia_secdata,
> +						iattrs->ia_secdata_len);
>  	} else
>  		set_default_inode_attr(inode, sd->s_mode);
> 
> -
>  	/* initialize inode according to type */
>  	switch (sysfs_type(sd)) {
>  	case SYSFS_DIR:
> diff --git a/fs/sysfs/symlink.c b/fs/sysfs/symlink.c
> index 1d897ad..c5081ad 100644
> --- a/fs/sysfs/symlink.c
> +++ b/fs/sysfs/symlink.c
> @@ -16,6 +16,7 @@
>  #include <linux/kobject.h>
>  #include <linux/namei.h>
>  #include <linux/mutex.h>
> +#include <linux/security.h>
> 
>  #include "sysfs.h"
> 
> @@ -209,6 +210,7 @@ static void sysfs_put_link(struct dentry *dentry, struct nameidata *nd, void *co
>  }
> 
>  const struct inode_operations sysfs_symlink_inode_operations = {
> +	.setxattr = sysfs_setxattr,
>  	.readlink = generic_readlink,
>  	.follow_link = sysfs_follow_link,
>  	.put_link = sysfs_put_link,
> diff --git a/fs/sysfs/sysfs.h b/fs/sysfs/sysfs.h
> index 3fa0d98..af4c4e7 100644
> --- a/fs/sysfs/sysfs.h
> +++ b/fs/sysfs/sysfs.h
> @@ -8,6 +8,8 @@
>   * This file is released under the GPLv2.
>   */
> 
> +#include <linux/fs.h>
> +
>  struct sysfs_open_dirent;
> 
>  /* type-specific structures for sysfs_dirent->s_* union members */
> @@ -31,6 +33,12 @@ struct sysfs_elem_bin_attr {
>  	struct hlist_head	buffers;
>  };
> 
> +struct sysfs_inode_attrs {
> +	struct iattr	ia_iattr;
> +	void		*ia_secdata;
> +	u32		ia_secdata_len;
> +};
> +
>  /*
>   * sysfs_dirent - the building block of sysfs hierarchy.  Each and
>   * every sysfs node is represented by single sysfs_dirent.
> @@ -56,7 +64,7 @@ struct sysfs_dirent {
>  	unsigned int		s_flags;
>  	ino_t			s_ino;
>  	umode_t			s_mode;
> -	struct iattr		*s_iattr;
> +	struct sysfs_inode_attrs *s_iattr;
>  };
> 
>  #define SD_DEACTIVATED_BIAS		INT_MIN
> @@ -148,6 +156,8 @@ static inline void __sysfs_put(struct sysfs_dirent *sd)
>  struct inode *sysfs_get_inode(struct sysfs_dirent *sd);
>  void sysfs_delete_inode(struct inode *inode);
>  int sysfs_setattr(struct dentry *dentry, struct iattr *iattr);
> +int sysfs_setxattr(struct dentry *dentry, const char *name, const void *value,
> +		size_t size, int flags);
>  int sysfs_hash_and_remove(struct sysfs_dirent *dir_sd, const char *name);
>  int sysfs_inode_init(void);
> 
> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> index f1d5677..38ed894 100644
> --- a/security/selinux/hooks.c
> +++ b/security/selinux/hooks.c
> @@ -448,6 +448,10 @@ static int sb_finish_set_opts(struct super_block *sb)
>  	    sbsec->behavior > ARRAY_SIZE(labeling_behaviors))
>  		sbsec->flags &= ~SE_SBLABELSUPP;
> 
> +	/* Special handling for sysfs. Is genfs but also has setxattr handler*/
> +	if (strncmp(sb->s_type->name, "sysfs", sizeof("sysfs")) == 0)
> +		sbsec->flags |= SE_SBLABELSUPP;
> +
>  	/* Initialize the root inode. */
>  	rc = inode_doinit_with_dentry(root_inode, root);
> 
> -- 
> 1.5.6.6
> 
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