• Eric W. Biederman's avatar
    mm: Add a user_ns owner to mm_struct and fix ptrace permission checks · bfedb589
    Eric W. Biederman authored
    During exec dumpable is cleared if the file that is being executed is
    not readable by the user executing the file.  A bug in
    ptrace_may_access allows reading the file if the executable happens to
    enter into a subordinate user namespace (aka clone(CLONE_NEWUSER),
    unshare(CLONE_NEWUSER), or setns(fd, CLONE_NEWUSER).
    This problem is fixed with only necessary userspace breakage by adding
    a user namespace owner to mm_struct, captured at the time of exec, so
    it is clear in which user namespace CAP_SYS_PTRACE must be present in
    to be able to safely give read permission to the executable.
    The function ptrace_may_access is modified to verify that the ptracer
    has CAP_SYS_ADMIN in task->mm->user_ns instead of task->cred->user_ns.
    This ensures that if the task changes it's cred into a subordinate
    user namespace it does not become ptraceable.
    The function ptrace_attach is modified to only set PT_PTRACE_CAP when
    CAP_SYS_PTRACE is held over task->mm->user_ns.  The intent of
    PT_PTRACE_CAP is to be a flag to note that whatever permission changes
    the task might go through the tracer has sufficient permissions for
    it not to be an issue.  task->cred->user_ns is always the same
    as or descendent of mm->user_ns.  Which guarantees that having
    CAP_SYS_PTRACE over mm->user_ns is the worst case for the tasks
    To prevent regressions mm->dumpable and mm->user_ns are not considered
    when a task has no mm.  As simply failing ptrace_may_attach causes
    regressions in privileged applications attempting to read things
    such as /proc/<pid>/stat
    Cc: stable@vger.kernel.org
    Acked-by: default avatarKees Cook <keescook@chromium.org>
    Tested-by: default avatarCyrill Gorcunov <gorcunov@openvz.org>
    Fixes: 8409cca7 ("userns: allow ptrace from non-init user namespaces")
    Signed-off-by: default avatar"Eric W. Biederman" <ebiederm@xmission.com>
ptrace.c 31.6 KB