Re: [PATCH -V6 11/26] vfs: Add permission flags for setting fileattributes

[J. Bruce Fields]

On Mon, Sep 05, 2011 at 10:55:33PM +0530, Aneesh Kumar K.V wrote:
> From: Andreas Gruenbacher <agruen@xxxxxxxxxx>
> 
> Some permission models can allow processes to take ownership of a file,
> change the file permissions, and set the file timestamps.  Introduce new
> permission mask flags and check for those permissions in
> inode_change_ok().

These little helper functions seem like they might be reasonable cleanup
even without the richacl_change_ok() piece; wonder if it'd be worth
splitting out the cleanup and applying it now?

Not that it's necessary--seems like a straightforward enough patch as
is.

--b.

> 
> Signed-off-by: Andreas Gruenbacher <agruen@xxxxxxxxxx>
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxxxxxxx>
> ---
>  fs/attr.c          |   70 +++++++++++++++++++++++++++++++++++++++++++--------
>  fs/namei.c         |    2 +-
>  include/linux/fs.h |    4 +++
>  3 files changed, 64 insertions(+), 12 deletions(-)
> 
> diff --git a/fs/attr.c b/fs/attr.c
> index f15e9e3..00578b9 100644
> --- a/fs/attr.c
> +++ b/fs/attr.c
> @@ -14,6 +14,55 @@
>  #include <linux/fcntl.h>
>  #include <linux/security.h>
>  
> +static int richacl_change_ok(struct inode *inode, int mask)
> +{
> +	if (!IS_RICHACL(inode))
> +		return -EPERM;
> +
> +	if (inode->i_op->permission)
> +		return inode->i_op->permission(inode, mask);
> +
> +	return check_acl(inode, mask);
> +}
> +
> +static bool inode_uid_change_ok(struct inode *inode, uid_t ia_uid)
> +{
> +	if (current_fsuid() == inode->i_uid && ia_uid == inode->i_uid)
> +		return true;
> +	if (current_fsuid() == ia_uid &&
> +	    richacl_change_ok(inode, MAY_TAKE_OWNERSHIP) == 0)
> +		return true;
> +	if (capable(CAP_CHOWN))
> +		return true;
> +	return false;
> +}
> +
> +static bool inode_gid_change_ok(struct inode *inode, gid_t ia_gid)
> +{
> +	int in_group = in_group_p(ia_gid);
> +	if (current_fsuid() == inode->i_uid &&
> +	    (in_group || ia_gid == inode->i_gid))
> +		return true;
> +	if (in_group && richacl_change_ok(inode, MAY_TAKE_OWNERSHIP) == 0)
> +		return true;
> +	if (capable(CAP_CHOWN))
> +		return true;
> +	return false;
> +}
> +
> +static bool inode_owner_permitted_or_capable(struct inode *inode, int mask)
> +{
> +	struct user_namespace *ns = inode_userns(inode);
> +
> +	if (current_user_ns() == ns && current_fsuid() == inode->i_uid)
> +		return true;
> +	if (richacl_change_ok(inode, mask) == 0)
> +		return true;
> +	if (ns_capable(ns, CAP_FOWNER))
> +		return true;
> +	return false;
> +}
> +
>  /**
>   * inode_change_ok - check if attribute changes to an inode are allowed
>   * @inode:	inode to check
> @@ -45,21 +94,20 @@ int inode_change_ok(struct inode *inode, struct iattr *attr)
>  		return 0;
>  
>  	/* Make sure a caller can chown. */
> -	if ((ia_valid & ATTR_UID) &&
> -	    (current_fsuid() != inode->i_uid ||
> -	     attr->ia_uid != inode->i_uid) && !capable(CAP_CHOWN))
> -		return -EPERM;
> +	if (ia_valid & ATTR_UID) {
> +		if (!inode_uid_change_ok(inode, attr->ia_uid))
> +			return -EPERM;
> +	}
>  
>  	/* Make sure caller can chgrp. */
> -	if ((ia_valid & ATTR_GID) &&
> -	    (current_fsuid() != inode->i_uid ||
> -	    (!in_group_p(attr->ia_gid) && attr->ia_gid != inode->i_gid)) &&
> -	    !capable(CAP_CHOWN))
> -		return -EPERM;
> +	if (ia_valid & ATTR_GID) {
> +		if (!inode_gid_change_ok(inode, attr->ia_gid))
> +			return -EPERM;
> +	}
>  
>  	/* Make sure a caller can chmod. */
>  	if (ia_valid & ATTR_MODE) {
> -		if (!inode_owner_or_capable(inode))
> +		if (!inode_owner_permitted_or_capable(inode, MAY_CHMOD))
>  			return -EPERM;
>  		/* Also check the setgid bit! */
>  		if (!in_group_p((ia_valid & ATTR_GID) ? attr->ia_gid :
> @@ -69,7 +117,7 @@ int inode_change_ok(struct inode *inode, struct iattr *attr)
>  
>  	/* Check for setting the inode time. */
>  	if (ia_valid & (ATTR_MTIME_SET | ATTR_ATIME_SET | ATTR_TIMES_SET)) {
> -		if (!inode_owner_or_capable(inode))
> +		if (!inode_owner_permitted_or_capable(inode, MAY_SET_TIMES))
>  			return -EPERM;
>  	}
>  
> diff --git a/fs/namei.c b/fs/namei.c
> index eacb530..a4d61d1 100644
> --- a/fs/namei.c
> +++ b/fs/namei.c
> @@ -174,7 +174,7 @@ void putname(const char *name)
>  EXPORT_SYMBOL(putname);
>  #endif
>  
> -static int check_acl(struct inode *inode, int mask)
> +int check_acl(struct inode *inode, int mask)
>  {
>  #ifdef CONFIG_FS_POSIX_ACL
>  	struct posix_acl *acl;
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 8afb054..8d5d6e4 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -71,6 +71,9 @@ struct inodes_stat_t {
>  #define MAY_CREATE_DIR		0x00000200
>  #define MAY_DELETE_CHILD	0x00000400
>  #define MAY_DELETE_SELF		0x00000800
> +#define MAY_TAKE_OWNERSHIP	0x00001000
> +#define MAY_CHMOD		0x00002000
> +#define MAY_SET_TIMES		0x00004000
>  
>  /*
>   * flags in file.f_mode.  Note that FMODE_READ and FMODE_WRITE must correspond
> @@ -2234,6 +2237,7 @@ extern sector_t bmap(struct inode *, sector_t);
>  extern int notify_change(struct dentry *, struct iattr *);
>  extern int inode_permission(struct inode *, int);
>  extern int generic_permission(struct inode *, int);
> +extern int check_acl(struct inode *, int);
>  
>  static inline bool execute_ok(struct inode *inode)
>  {
> -- 
> 1.7.4.1
> 
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