• Kees Cook's avatar
    binfmt: Introduce secureexec flag · c425e189
    Kees Cook authored
    The bprm_secureexec hook can be moved earlier. Right now, it is called
    during create_elf_tables(), via load_binary(), via search_binary_handler(),
    via exec_binprm(). Nearly all (see exception below) state used by
    bprm_secureexec is created during the bprm_set_creds hook, called from
    For all LSMs (except commoncaps described next), only the first execution
    of bprm_set_creds takes any effect (they all check bprm->called_set_creds
    which prepare_binprm() sets after the first call to the bprm_set_creds
    hook).  However, all these LSMs also only do anything with bprm_secureexec
    when they detected a secure state during their first run of bprm_set_creds.
    Therefore, it is functionally identical to move the detection into
    bprm_set_creds, since the results from secureexec here only need to be
    based on the first call to the LSM's bprm_set_creds hook.
    The single exception is that the commoncaps secureexec hook also examines
    euid/uid and egid/gid differences which are controlled by bprm_fill_uid(),
    via prepare_binprm(), which can be called multiple times (e.g.
    binfmt_script, binfmt_misc), and may clear the euid/egid for the final
    load (i.e. the script interpreter). However, while commoncaps specifically
    ignores bprm->cred_prepared, and runs its bprm_set_creds hook each time
    prepare_binprm() may get called, it needs to base the secureexec decision
    on the final call to bprm_set_creds. As a result, it will need special
    To begin this refactoring, this adds the secureexec flag to the bprm
    struct, and calls the secureexec hook during setup_new_exec(). This is
    safe since all the cred work is finished (and past the point of no return).
    This explicit call will be removed in later patches once the hook has been
    Cc: David Howells <dhowells@redhat.com>
    Signed-off-by: default avatarKees Cook <keescook@chromium.org>
    Reviewed-by: default avatarJohn Johansen <john.johansen@canonical.com>
    Acked-by: default avatarSerge Hallyn <serge@hallyn.com>
    Reviewed-by: default avatarJames Morris <james.l.morris@oracle.com>
binfmt_elf.c 62.8 KB