RE: [PATCH v5 2/5] bpf: Add bpf_lookup_user_key() and bpf_key_put() helpers

[Roberto Sassu <roberto.sassu@huawei.com>]

> From: Alexei Starovoitov [mailto:alexei.starovoitov@gmail.com]
> Sent: Wednesday, June 22, 2022 12:33 AM
> On Tue, Jun 21, 2022 at 06:37:54PM +0200, Roberto Sassu wrote:
> > Add the bpf_lookup_user_key() and bpf_key_put() helpers, to respectively
> > search a key with a given serial, and release the reference count of the
> > found key.
> >
> > Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
> > ---
> >  include/uapi/linux/bpf.h       | 16 ++++++++++++
> >  kernel/bpf/bpf_lsm.c           | 46 ++++++++++++++++++++++++++++++++++
> >  kernel/bpf/verifier.c          |  6 +++--
> >  scripts/bpf_doc.py             |  2 ++
> >  tools/include/uapi/linux/bpf.h | 16 ++++++++++++
> >  5 files changed, 84 insertions(+), 2 deletions(-)
> >
> > diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> > index e81362891596..7bbcf2cd105d 100644
> > --- a/include/uapi/linux/bpf.h
> > +++ b/include/uapi/linux/bpf.h
> > @@ -5325,6 +5325,20 @@ union bpf_attr {
> >   *		**-EACCES** if the SYN cookie is not valid.
> >   *
> >   *		**-EPROTONOSUPPORT** if CONFIG_IPV6 is not builtin.
> > + *
> > + * struct key *bpf_lookup_user_key(u32 serial, unsigned long flags)
> > + *	Description
> > + *		Search a key with a given *serial* and the provided *flags*, and
> > + *		increment the reference count of the key.
> 
> Why passing 'flags' is ok to do?
> Please think through every line of the patch.

To be honest, I thought about it. Probably yes, I should do some
sanitization, like I did for the keyring ID. When I checked
lookup_user_key(), I saw that flags are checked individually, so
an arbitrary value passed to the helper should not cause harm.
Will do sanitization, if you prefer. It is just that we have to keep
the eBPF code in sync with key flag definition (unless we have
a 'last' flag).

Thanks

Roberto

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