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    SubjectRe: [RFC][PATCH 0/7] File descriptor labeling
    On 4/27/2011 5:34 AM, Roberto Sassu wrote:
    > File descriptor labeling issue
    > Actually SELinux and SMACK assign to file descriptors the same label of the
    > opening process and use it in LSM hooks security_file_permission(),
    > security_file_fcntl() and others to verify if the 'current' process has the
    > rights to perform the requested operation.
    > Using the credentials of the 'current' process may be not appropriate in
    > case a file descriptor is opened by a kernel service (i.e. a filesystem)
    > and made shared among user processes. For instance, in a system with
    > SELinux and eCryptfs, if the process A opens an encrypted file, eCryptfs
    > obtains a file descriptor to access the correspondent inode in the lower
    > filesystem, labeled with the A's label.
    > If the process B accesses the same encrypted file, it needs the 'use'
    > permission on the A's label other than permissions for the lower inode.
    > However, if B is the first accessing process, A needs the 'use' permission
    > on the B's label.
    > The solution proposed is to modify those kernel services that deal with
    > file descriptors to provide their set of credentials to dentry_open(), so
    > that obtained objects are labeled with a unique label. In this way, in the
    > above example, if eCryptfs provides its credentials with the label C to
    > dentry_open(), all user processes need the 'use' permission only on C.
    > File descriptor labeling and IMA
    > The above proposal suggests to use the file descriptor label as a new
    > criteria in the IMA policy to determine if a file must be measured. It will
    > be possible to measure all files opened by a kernel service by simply
    > writing a rule where the file descriptor label given as a value matches the
    > one provided by the same service together with other credentials to the
    > function dentry_open().
    > In the above example, if eCryptfs provides its credentials with the label C
    > to dentry_open(), it is possible to measure all inodes opened in the lower
    > filesystem by specifying a rule like:
    > fowner_type=C
    > The benefits of this new criteria will be greater with the integration of
    > EVM and the IMA appraisal feature in the kernel. ECryptfs can be used in
    > conjunction with these components to verify the integrity of the content
    > and extended attributes of encrypted files.
    > Roberto Sassu
    > Roberto Sassu (7):
    > fs: initialize file->f_cred with credentials provided
    > selinux: label new file descriptors using file->f_cred
    > smack: assign the label set in file->f_cred to new file descriptors
    > smack: fix label check in smack_kernel_act_as()
    > smack: import the security label in smack_secctx_to_secid()
    > security: new LSM hook security_file_getsecid()
    > ima: added new LSM conditions in the policy
    > Documentation/ABI/testing/ima_policy | 7 ++++-
    > fs/file_table.c | 5 +--
    > fs/internal.h | 2 +-
    > fs/namei.c | 2 +-
    > fs/open.c | 2 +-
    > include/linux/security.h | 12 +++++++++
    > security/capability.c | 6 ++++
    > security/integrity/ima/ima.h | 4 +-
    > security/integrity/ima/ima_api.c | 4 +-
    > security/integrity/ima/ima_main.c | 4 +-
    > security/integrity/ima/ima_policy.c | 45 +++++++++++++++++++++++++++++----
    > security/security.c | 6 ++++
    > security/selinux/hooks.c | 9 ++++++-
    > security/smack/smack_lsm.c | 23 +++++++++++++++--
    > 14 files changed, 108 insertions(+), 23 deletions(-)

    I have not given this patch set a complete review, but at first
    glance I do not like it. You seem to be making a lot of assumptions
    about the interactions between services and LSMs that I don't
    know are valid. It is possible that I have not dug in deeply
    enough to understand where this is headed. I will have a more
    complete review in a bit.

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