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    Subject[PATCH -V7 14/26] richacl: Permission mapping functions
    Date
    From: Andreas Gruenbacher <agruen@kernel.org>

    We need to map from POSIX permissions to NFSv4 permissions when a
    chmod() is done, from NFSv4 permissions to POSIX permissions when an acl
    is set (which implicitly sets the file permission bits), and from the
    MAY_READ/MAY_WRITE/MAY_EXEC/MAY_APPEND flags to NFSv4 permissions when
    doing an access check in a richacl.

    Acked-by: David Howells <dhowells@redhat.com>
    Signed-off-by: Andreas Gruenbacher <agruen@kernel.org>
    Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
    ---
    fs/richacl_base.c | 117 +++++++++++++++++++++++++++++++++++++++++++++++
    include/linux/richacl.h | 46 ++++++++++++++++++
    2 files changed, 163 insertions(+), 0 deletions(-)

    diff --git a/fs/richacl_base.c b/fs/richacl_base.c
    index 3536626..b6460a9 100644
    --- a/fs/richacl_base.c
    +++ b/fs/richacl_base.c
    @@ -69,6 +69,123 @@ richacl_clone(const struct richacl *acl)
    }

    /**
    + * richacl_mask_to_mode - compute the file permission bits which correspond to @mask
    + * @mask: %ACE4_* permission mask
    + *
    + * See richacl_masks_to_mode().
    + */
    +static int
    +richacl_mask_to_mode(unsigned int mask)
    +{
    + int mode = 0;
    +
    + if (mask & ACE4_POSIX_MODE_READ)
    + mode |= MAY_READ;
    + if (mask & ACE4_POSIX_MODE_WRITE)
    + mode |= MAY_WRITE;
    + if (mask & ACE4_POSIX_MODE_EXEC)
    + mode |= MAY_EXEC;
    +
    + return mode;
    +}
    +
    +/**
    + * richacl_masks_to_mode - compute the file permission bits from the file masks
    + *
    + * When setting a richacl, we set the file permission bits to indicate maximum
    + * permissions: for example, we set the Write permission when a mask contains
    + * ACE4_APPEND_DATA even if it does not also contain ACE4_WRITE_DATA.
    + *
    + * Permissions which are not in ACE4_POSIX_MODE_READ, ACE4_POSIX_MODE_WRITE, or
    + * ACE4_POSIX_MODE_EXEC cannot be represented in the file permission bits.
    + * Such permissions can still be effective, but not for new files or after a
    + * chmod(), and only if they were set explicitly, for example, by setting a
    + * richacl.
    + */
    +int
    +richacl_masks_to_mode(const struct richacl *acl)
    +{
    + return richacl_mask_to_mode(acl->a_owner_mask) << 6 |
    + richacl_mask_to_mode(acl->a_group_mask) << 3 |
    + richacl_mask_to_mode(acl->a_other_mask);
    +}
    +EXPORT_SYMBOL_GPL(richacl_masks_to_mode);
    +
    +/**
    + * richacl_mode_to_mask - compute a file mask from the lowest three mode bits
    + *
    + * When the file permission bits of a file are set with chmod(), this specifies
    + * the maximum permissions that processes will get. All permissions beyond
    + * that will be removed from the file masks, and become ineffective.
    + *
    + * We also add in the permissions which are always allowed no matter what the
    + * acl says.
    + */
    +unsigned int
    +richacl_mode_to_mask(mode_t mode)
    +{
    + unsigned int mask = ACE4_POSIX_ALWAYS_ALLOWED;
    +
    + if (mode & MAY_READ)
    + mask |= ACE4_POSIX_MODE_READ;
    + if (mode & MAY_WRITE)
    + mask |= ACE4_POSIX_MODE_WRITE;
    + if (mode & MAY_EXEC)
    + mask |= ACE4_POSIX_MODE_EXEC;
    +
    + return mask;
    +}
    +
    +/**
    + * richacl_want_to_mask - convert the iop->permission want argument to a mask
    + * @want: @want argument of the permission inode operation
    + *
    + * When checking for append, @want is (MAY_WRITE | MAY_APPEND).
    + *
    + * Richacls use the iop->may_create and iop->may_delete hooks which are
    + * used for checking if creating and deleting files is allowed. These hooks do
    + * not use richacl_want_to_mask(), so we do not have to deal with mapping
    + * MAY_WRITE to ACE4_ADD_FILE, ACE4_ADD_SUBDIRECTORY, and ACE4_DELETE_CHILD
    + * here.
    + */
    +unsigned int
    +richacl_want_to_mask(unsigned int want)
    +{
    + unsigned int mask = 0;
    +
    + if (want & MAY_READ)
    + mask |= ACE4_READ_DATA;
    + if (want & MAY_DELETE_SELF)
    + mask |= ACE4_DELETE;
    + if (want & MAY_TAKE_OWNERSHIP)
    + mask |= ACE4_WRITE_OWNER;
    + if (want & MAY_CHMOD)
    + mask |= ACE4_WRITE_ACL;
    + if (want & MAY_SET_TIMES)
    + mask |= ACE4_WRITE_ATTRIBUTES;
    + if (want & MAY_EXEC)
    + mask |= ACE4_EXECUTE;
    + /*
    + * differentiate MAY_WRITE from these request
    + */
    + if (want & (MAY_APPEND |
    + MAY_CREATE_FILE | MAY_CREATE_DIR |
    + MAY_DELETE_CHILD)) {
    + if (want & MAY_APPEND)
    + mask |= ACE4_APPEND_DATA;
    + if (want & MAY_CREATE_FILE)
    + mask |= ACE4_ADD_FILE;
    + if (want & MAY_CREATE_DIR)
    + mask |= ACE4_ADD_SUBDIRECTORY;
    + if (want & MAY_DELETE_CHILD)
    + mask |= ACE4_DELETE_CHILD;
    + } else if (want & MAY_WRITE)
    + mask |= ACE4_WRITE_DATA;
    + return mask;
    +}
    +EXPORT_SYMBOL_GPL(richacl_want_to_mask);
    +
    +/**
    * richace_is_same_identifier - are both identifiers the same?
    */
    int
    diff --git a/include/linux/richacl.h b/include/linux/richacl.h
    index 745cfc1..61f1b8a 100644
    --- a/include/linux/richacl.h
    +++ b/include/linux/richacl.h
    @@ -117,6 +117,49 @@ struct richacl {
    ACE4_WRITE_OWNER | \
    ACE4_SYNCHRONIZE)

    +/*
    + * The POSIX permissions are supersets of the following NFSv4 permissions:
    + *
    + * - MAY_READ maps to READ_DATA or LIST_DIRECTORY, depending on the type
    + * of the file system object.
    + *
    + * - MAY_WRITE maps to WRITE_DATA or ACE4_APPEND_DATA for files, and to
    + * ADD_FILE, ACE4_ADD_SUBDIRECTORY, or ACE4_DELETE_CHILD for directories.
    + *
    + * - MAY_EXECUTE maps to ACE4_EXECUTE.
    + *
    + * (Some of these NFSv4 permissions have the same bit values.)
    + */
    +#define ACE4_POSIX_MODE_READ ( \
    + ACE4_READ_DATA | \
    + ACE4_LIST_DIRECTORY)
    +#define ACE4_POSIX_MODE_WRITE ( \
    + ACE4_WRITE_DATA | \
    + ACE4_ADD_FILE | \
    + ACE4_APPEND_DATA | \
    + ACE4_ADD_SUBDIRECTORY | \
    + ACE4_DELETE_CHILD)
    +#define ACE4_POSIX_MODE_EXEC ACE4_EXECUTE
    +#define ACE4_POSIX_MODE_ALL ( \
    + ACE4_POSIX_MODE_READ | \
    + ACE4_POSIX_MODE_WRITE | \
    + ACE4_POSIX_MODE_EXEC)
    +/*
    + * These permissions are always allowed
    + * no matter what the acl says.
    + */
    +#define ACE4_POSIX_ALWAYS_ALLOWED ( \
    + ACE4_SYNCHRONIZE | \
    + ACE4_READ_ATTRIBUTES | \
    + ACE4_READ_ACL)
    +/*
    + * The owner is implicitly granted
    + * these permissions under POSIX.
    + */
    +#define ACE4_POSIX_OWNER_ALLOWED ( \
    + ACE4_WRITE_ATTRIBUTES | \
    + ACE4_WRITE_OWNER | \
    + ACE4_WRITE_ACL)
    /**
    * richacl_get - grab another reference to a richacl handle
    */
    @@ -241,5 +284,8 @@ extern struct richacl *richacl_alloc(int);
    extern int richace_is_same_identifier(const struct richace *,
    const struct richace *);
    extern int richace_set_who(struct richace *, const char *);
    +extern int richacl_masks_to_mode(const struct richacl *);
    +extern unsigned int richacl_mode_to_mask(mode_t);
    +extern unsigned int richacl_want_to_mask(unsigned int);

    #endif /* __RICHACL_H */
    --
    1.7.5.4


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