[PATCH v1] security: add trace event for cap_capable

[Paul Moore]

On Oct 24, 2024 Jordan Rome <linux at jordanrome.com> wrote:
> 
> In cases where we want a stable way to observe/trace
> cap_capable (e.g. protection from inlining and API updates)
> add a tracepoint that passes:
> - The credentials used
> - The user namespace which needs the capability
> - The user namespace that actually has the capability (if one exists)
> - The capability to check for
> - Bitmask of options defined in include/linux/security.h
> - The return value of the check
> 
> Signed-off-by: Jordan Rome <linux at jordanrome.com>
> ---
>  MAINTAINERS                       |  1 +
>  include/trace/events/capability.h | 58 +++++++++++++++++++++++++++++++
>  security/commoncap.c              | 21 +++++++----
>  3 files changed, 74 insertions(+), 6 deletions(-)
>  create mode 100644 include/trace/events/capability.h

...

> diff --git a/include/trace/events/capability.h b/include/trace/events/capability.h
> new file mode 100644
> index 000000000000..092b8e77063a
> --- /dev/null
> +++ b/include/trace/events/capability.h
> @@ -0,0 +1,58 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#undef TRACE_SYSTEM
> +#define TRACE_SYSTEM capability
> +
> +#if !defined(_TRACE_CAPABILITY_H) || defined(TRACE_HEADER_MULTI_READ)
> +#define _TRACE_CAPABILITY_H
> +
> +#include <linux/cred.h>
> +#include <linux/tracepoint.h>
> +#include <linux/user_namespace.h>
> +
> +/**
> + * capable - called after it's determined if a task has a particular
> + * effective capability
> + *
> + * @cred: The credentials used
> + * @targ_ns:  The user namespace which needs the capability
> + * @capable_ns:  The user namespace that actually has the capability
> + *               if ret is 0 otherwise this will be NULL
> + * @cap: The capability to check for
> + * @opts: Bitmask of options defined in include/linux/security.h
> + * @ret: The return value of the check: 0 if it does, -ve if it does not
> + *
> + * Allows to trace calls to cap_capable in commoncap.c
> + */
> +TRACE_EVENT(capable,

This should either be named "cap_capable" if you are only interested in
the CAP_XXX capability checks or "capable" if you are interested in all
of the checks that are performed when capable() is called from within
the kernel.  Presently safesetid, apparmor, and selinux all enforce
access controls when capable() is called, with the potential for
additional checks in future kernel releases.

> +	TP_PROTO(const struct cred *cred, struct user_namespace *targ_ns,
> +		struct user_namespace *capable_ns, int cap, unsigned int opts, int ret),
> +
> +	TP_ARGS(cred, targ_ns, capable_ns, cap, opts, ret),
> +
> +	TP_STRUCT__entry(
> +		__field(const struct cred *, cred)
> +		__field(struct user_namespace *, targ_ns)
> +		__field(struct user_namespace *, capable_ns)
> +		__field(int, cap)
> +		__field(unsigned int, opts)
> +		__field(int, ret)
> +	),
> +
> +	TP_fast_assign(
> +		__entry->cred       = cred;
> +		__entry->targ_ns    = targ_ns;
> +		__entry->capable_ns = capable_ns;
> +		__entry->cap        = cap;
> +		__entry->opts       = opts;
> +		__entry->ret        = ret;
> +	),
> +
> +	TP_printk("cap %d, opts %u, ret %d",
> +		__entry->cap, __entry->opts, __entry->ret)
> +);
> +
> +#endif /* _TRACE_CAPABILITY_H */
> +
> +/* This part must be outside protection */
> +#include <trace/define_trace.h>

--
paul-moore.com