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Date: Wed, 4 Dec 2019 15:08:27 +0100
From: Jiri Olsa <jolsa@...hat.com>
To: Paul Moore <paul@...l-moore.com>
Cc: Jiri Olsa <jolsa@...nel.org>, Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>, netdev@...r.kernel.org,
bpf@...r.kernel.org, linux-audit@...hat.com,
Andrii Nakryiko <andriin@...com>, Yonghong Song <yhs@...com>,
Martin KaFai Lau <kafai@...com>,
Jakub Kicinski <jakub.kicinski@...ronome.com>,
Steve Grubb <sgrubb@...hat.com>,
David Miller <davem@...hat.com>,
Eric Paris <eparis@...hat.com>, Jiri Benc <jbenc@...hat.com>
Subject: Re: [RFC] bpf: Emit audit messages upon successful prog load and
unload
On Tue, Dec 03, 2019 at 09:53:16PM -0500, Paul Moore wrote:
SNIP
> > >
> > > static inline void audit_foo(...)
> > > {
> > > if (unlikely(!audit_dummy_context()))
> > > __audit_foo(...)
> > > }
> >
> > bpf_audit_prog might be called outside of syscall context for UNLOAD event,
> > so that would prevent it from being stored
>
> Okay, right. More on this below ...
>
> > I can see audit_log_start checks on value of audit_context() that we pass in,
>
> The check in audit_log_start() is for a different reason; it checks
> the passed context to see if it should associate the record with
> others in the same event, e.g. PATH records associated with the
> matching SYSCALL record. This way all the associated records show up
> as part of the same event (as defined by the audit timestamp).
>
> > should we check for audit_dummy_context just for load event? like:
> >
> >
> > static void bpf_audit_prog(const struct bpf_prog *prog, enum bpf_audit op)
> > {
> > struct audit_buffer *ab;
> >
> > if (audit_enabled == AUDIT_OFF)
> > return;
> > if (op == BPF_AUDIT_LOAD && audit_dummy_context())
> > return;
> > ab = audit_log_start(audit_context(), GFP_ATOMIC, AUDIT_BPF);
> > if (unlikely(!ab))
> > return;
> > ...
> > }
>
> Ignoring the dummy context for a minute, there is likely a larger
> issue here with using audit_context() when bpf_audit_prog() is called
> outside of a syscall, e.g. BPF_AUDIT_UNLOAD. In this case we likely
> shouldn't be taking the audit context from the current task, we
> shouldn't be taking it from anywhere, it should be NULL.
>
> As far as the dummy context is concerned, you might want to skip the
> dummy context check since you can only do that on the LOAD side, which
> means that depending on the system's configuration you could end up
> with a number of unbalanced LOAD/UNLOAD events. The downside is that
> you are always going to get the BPF audit records on systemd based
> systems, since they ignore the admin's audit configuration and always
> enable audit (yes, we've tried to get systemd to change, they don't
> seem to care).
ok, so something like below?
thanks,
jirka
---
include/uapi/linux/audit.h | 1 +
kernel/bpf/syscall.c | 30 ++++++++++++++++++++++++++++++
2 files changed, 31 insertions(+)
diff --git a/include/uapi/linux/audit.h b/include/uapi/linux/audit.h
index c89c6495983d..32a5db900f47 100644
--- a/include/uapi/linux/audit.h
+++ b/include/uapi/linux/audit.h
@@ -116,6 +116,7 @@
#define AUDIT_FANOTIFY 1331 /* Fanotify access decision */
#define AUDIT_TIME_INJOFFSET 1332 /* Timekeeping offset injected */
#define AUDIT_TIME_ADJNTPVAL 1333 /* NTP value adjustment */
+#define AUDIT_BPF 1334 /* BPF subsystem */
#define AUDIT_AVC 1400 /* SE Linux avc denial or grant */
#define AUDIT_SELINUX_ERR 1401 /* Internal SE Linux Errors */
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index e3461ec59570..81f1a6308aa8 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -23,6 +23,7 @@
#include <linux/timekeeping.h>
#include <linux/ctype.h>
#include <linux/nospec.h>
+#include <linux/audit.h>
#include <uapi/linux/btf.h>
#define IS_FD_ARRAY(map) ((map)->map_type == BPF_MAP_TYPE_PERF_EVENT_ARRAY || \
@@ -1306,6 +1307,33 @@ static int find_prog_type(enum bpf_prog_type type, struct bpf_prog *prog)
return 0;
}
+enum bpf_audit {
+ BPF_AUDIT_LOAD,
+ BPF_AUDIT_UNLOAD,
+};
+
+static const char * const bpf_audit_str[] = {
+ [BPF_AUDIT_LOAD] = "LOAD",
+ [BPF_AUDIT_UNLOAD] = "UNLOAD",
+};
+
+static void bpf_audit_prog(const struct bpf_prog *prog, enum bpf_audit op)
+{
+ struct audit_context *ctx = NULL;
+ struct audit_buffer *ab;
+
+ if (audit_enabled == AUDIT_OFF)
+ return;
+ if (op == BPF_AUDIT_LOAD)
+ ctx = audit_context();
+ ab = audit_log_start(ctx, GFP_ATOMIC, AUDIT_BPF);
+ if (unlikely(!ab))
+ return;
+ audit_log_format(ab, "prog-id=%u op=%s",
+ prog->aux->id, bpf_audit_str[op]);
+ audit_log_end(ab);
+}
+
int __bpf_prog_charge(struct user_struct *user, u32 pages)
{
unsigned long memlock_limit = rlimit(RLIMIT_MEMLOCK) >> PAGE_SHIFT;
@@ -1421,6 +1449,7 @@ static void __bpf_prog_put(struct bpf_prog *prog, bool do_idr_lock)
{
if (atomic64_dec_and_test(&prog->aux->refcnt)) {
perf_event_bpf_event(prog, PERF_BPF_EVENT_PROG_UNLOAD, 0);
+ bpf_audit_prog(prog, BPF_AUDIT_UNLOAD);
/* bpf_prog_free_id() must be called first */
bpf_prog_free_id(prog, do_idr_lock);
__bpf_prog_put_noref(prog, true);
@@ -1830,6 +1859,7 @@ static int bpf_prog_load(union bpf_attr *attr, union bpf_attr __user *uattr)
*/
bpf_prog_kallsyms_add(prog);
perf_event_bpf_event(prog, PERF_BPF_EVENT_PROG_LOAD, 0);
+ bpf_audit_prog(prog, BPF_AUDIT_LOAD);
err = bpf_prog_new_fd(prog);
if (err < 0)
--
2.23.0
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