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    Subject[PATCH v12 05/49] vfs: Add permission flags for setting file attributes
    Date
    Richacls support permissions that allow to take ownership of a file,
    change the file permissions, and set the file timestamps. Support that
    by introducing new permission mask flags and by checking for those mask
    flags in inode_change_ok().

    Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
    Reviewed-by: J. Bruce Fields <bfields@redhat.com>
    ---
    fs/attr.c | 79 +++++++++++++++++++++++++++++++++++++++++++++---------
    include/linux/fs.h | 3 +++
    2 files changed, 70 insertions(+), 12 deletions(-)

    diff --git a/fs/attr.c b/fs/attr.c
    index 328be71..85483e0 100644
    --- a/fs/attr.c
    +++ b/fs/attr.c
    @@ -17,6 +17,65 @@
    #include <linux/ima.h>

    /**
    + * inode_extended_permission - permissions beyond read/write/execute
    + *
    + * Check for permissions that only richacls can currently grant.
    + */
    +static int inode_extended_permission(struct inode *inode, int mask)
    +{
    + if (!IS_RICHACL(inode))
    + return -EPERM;
    + return inode_permission(inode, mask);
    +}
    +
    +static bool inode_uid_change_ok(struct inode *inode, kuid_t ia_uid)
    +{
    + if (uid_eq(current_fsuid(), inode->i_uid) &&
    + uid_eq(ia_uid, inode->i_uid))
    + return true;
    + if (uid_eq(current_fsuid(), ia_uid) &&
    + inode_extended_permission(inode, MAY_TAKE_OWNERSHIP) == 0)
    + return true;
    + if (capable_wrt_inode_uidgid(inode, CAP_CHOWN))
    + return true;
    + return false;
    +}
    +
    +static bool inode_gid_change_ok(struct inode *inode, kgid_t ia_gid)
    +{
    + int in_group = in_group_p(ia_gid);
    + if (uid_eq(current_fsuid(), inode->i_uid) &&
    + (in_group || gid_eq(ia_gid, inode->i_gid)))
    + return true;
    + if (in_group && inode_extended_permission(inode, MAY_TAKE_OWNERSHIP) == 0)
    + return true;
    + if (capable_wrt_inode_uidgid(inode, CAP_CHOWN))
    + return true;
    + return false;
    +}
    +
    +/**
    + * inode_owner_permitted_or_capable
    + *
    + * Check for permissions implicitly granted to the owner, like MAY_CHMOD or
    + * MAY_SET_TIMES. Equivalent to inode_owner_or_capable for file systems
    + * without support for those permissions.
    + */
    +static bool inode_owner_permitted_or_capable(struct inode *inode, int mask)
    +{
    + struct user_namespace *ns;
    +
    + if (uid_eq(current_fsuid(), inode->i_uid))
    + return true;
    + if (inode_extended_permission(inode, mask) == 0)
    + return true;
    + ns = current_user_ns();
    + if (ns_capable(ns, CAP_FOWNER) && kuid_has_mapping(ns, inode->i_uid))
    + return true;
    + return false;
    +}
    +
    +/**
    * inode_change_ok - check if attribute changes to an inode are allowed
    * @inode: inode to check
    * @attr: attributes to change
    @@ -47,22 +106,18 @@ int inode_change_ok(struct inode *inode, struct iattr *attr)
    return 0;

    /* Make sure a caller can chown. */
    - if ((ia_valid & ATTR_UID) &&
    - (!uid_eq(current_fsuid(), inode->i_uid) ||
    - !uid_eq(attr->ia_uid, inode->i_uid)) &&
    - !capable_wrt_inode_uidgid(inode, 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) &&
    - (!uid_eq(current_fsuid(), inode->i_uid) ||
    - (!in_group_p(attr->ia_gid) && !gid_eq(attr->ia_gid, inode->i_gid))) &&
    - !capable_wrt_inode_uidgid(inode, 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 :
    @@ -73,7 +128,7 @@ 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/include/linux/fs.h b/include/linux/fs.h
    index aab32c8..ba91a89 100644
    --- a/include/linux/fs.h
    +++ b/include/linux/fs.h
    @@ -86,6 +86,9 @@ typedef void (dax_iodone_t)(struct buffer_head *bh_map, int uptodate);
    #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
    --
    2.5.0


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