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    SubjectRe: [PATCH v2 2/2] capabilities: Add a securebit to disable PR_CAP_AMBIENT_RAISE
    On Thu, May 14, 2015 at 11:39:49PM -0700, Andy Lutomirski wrote:
    > Per Andrew Morgan's request, add a securebit to allow admins to
    > disable PR_CAP_AMBIENT_RAISE. This securebit will prevent processes
    > from adding capabilities to their ambient set.
    >
    > For simplicity, this disables PR_CAP_AMBIENT_RAISE entirely rather
    > than just disabling setting previously cleared bits.
    >
    > Requested-by: Andrew G. Morgan <morgan@kernel.org>
    > Cc: Kees Cook <keescook@chromium.org>
    > Cc: Christoph Lameter <cl@linux.com>
    > Cc: Serge Hallyn <serge.hallyn@canonical.com>
    > Cc: Andy Lutomirski <luto@amacapital.net>
    > Cc: Jonathan Corbet <corbet@lwn.net>
    > Cc: Aaron Jones <aaronmdjones@gmail.com>
    > CC: Ted Ts'o <tytso@mit.edu>
    > Cc: linux-security-module@vger.kernel.org
    > Cc: linux-kernel@vger.kernel.org
    > Cc: linux-api@vger.kernel.org
    > Cc: akpm@linuxfoundation.org
    > Cc: Andrew G. Morgan <morgan@kernel.org>
    > Cc: Mimi Zohar <zohar@linux.vnet.ibm.com>
    > Cc: Austin S Hemmelgarn <ahferroin7@gmail.com>
    > Cc: Markku Savela <msa@moth.iki.fi>
    > Cc: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
    > Cc: Michael Kerrisk <mtk.manpages@gmail.com>
    > Signed-off-by: Andy Lutomirski <luto@kernel.org>

    Interesting - at first I thought this wouldn't please Andrew as he'd
    want the inverse, but I guess this way keeps the pure-capabilities
    mode (with SECURE_ALL_BITS set) ambient-free which I suppose is
    really the important thing.

    Acked-by: Serge Hallyn <serge.hallyn@canonical.com>

    > ---
    > include/uapi/linux/securebits.h | 11 ++++++++++-
    > security/commoncap.c | 3 ++-
    > 2 files changed, 12 insertions(+), 2 deletions(-)
    >
    > diff --git a/include/uapi/linux/securebits.h b/include/uapi/linux/securebits.h
    > index 985aac9e6bf8..35ac35cef217 100644
    > --- a/include/uapi/linux/securebits.h
    > +++ b/include/uapi/linux/securebits.h
    > @@ -43,9 +43,18 @@
    > #define SECBIT_KEEP_CAPS (issecure_mask(SECURE_KEEP_CAPS))
    > #define SECBIT_KEEP_CAPS_LOCKED (issecure_mask(SECURE_KEEP_CAPS_LOCKED))
    >
    > +/* When set, a process cannot add new capabilities to its ambient set. */
    > +#define SECURE_NO_CAP_AMBIENT_RAISE 6
    > +#define SECURE_NO_CAP_AMBIENT_RAISE_LOCKED 7 /* make bit-6 immutable */
    > +
    > +#define SECBIT_NO_CAP_AMBIENT_RAISE (issecure_mask(SECURE_NO_CAP_AMBIENT_RAISE))
    > +#define SECBIT_NO_CAP_AMBIENT_RAISE_LOCKED \
    > + (issecure_mask(SECURE_NO_CAP_AMBIENT_RAISE_LOCKED))
    > +
    > #define SECURE_ALL_BITS (issecure_mask(SECURE_NOROOT) | \
    > issecure_mask(SECURE_NO_SETUID_FIXUP) | \
    > - issecure_mask(SECURE_KEEP_CAPS))
    > + issecure_mask(SECURE_KEEP_CAPS) | \
    > + issecure_mask(SECURE_NO_CAP_AMBIENT_RAISE))
    > #define SECURE_ALL_LOCKS (SECURE_ALL_BITS << 1)
    >
    > #endif /* _UAPI_LINUX_SECUREBITS_H */
    > diff --git a/security/commoncap.c b/security/commoncap.c
    > index 09541a6a85a0..98aa1b129c12 100644
    > --- a/security/commoncap.c
    > +++ b/security/commoncap.c
    > @@ -983,7 +983,8 @@ int cap_task_prctl(int option, unsigned long arg2, unsigned long arg3,
    > if (arg2 == PR_CAP_AMBIENT_RAISE &&
    > (!cap_raised(current_cred()->cap_permitted, arg3) ||
    > !cap_raised(current_cred()->cap_inheritable,
    > - arg3)))
    > + arg3) ||
    > + issecure(SECURE_NO_CAP_AMBIENT_RAISE)))
    > return -EPERM;
    >
    > new = prepare_creds();
    > --
    > 2.1.0
    >
    > --
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