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Date: Wed, 7 Sep 2011 16:55:03 -0400
From: "J. Bruce Fields" <bfields@...ldses.org>
To: "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
Cc: agruen@...nel.org, akpm@...ux-foundation.org, dhowells@...hat.com,
linux-fsdevel@...r.kernel.org, linux-nfs@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH -V6 11/26] vfs: Add permission flags for setting file
attributes
On Mon, Sep 05, 2011 at 10:55:33PM +0530, Aneesh Kumar K.V wrote:
> From: Andreas Gruenbacher <agruen@...nel.org>
>
> 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@...nel.org>
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@...ux.vnet.ibm.com>
> ---
> 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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