[PATCH v3 1/2] bpf: restore the ebpf program ID for BPF_AUDIT_UNLOAD and PERF_BPF_EVENT_PROG_UNLOAD

[Paul Moore]

When changing the ebpf program put() routines to support being called
from within IRQ context the program ID was reset to zero prior to
calling the perf event and audit UNLOAD record generators, which
resulted in problems as the ebpf program ID was bogus (always zero).
This patch addresses this problem by removing an unnecessary call to
bpf_prog_free_id() in __bpf_prog_offload_destroy() and adjusting
__bpf_prog_put() to only call bpf_prog_free_id() after audit and perf
have finished their bpf program unload tasks in
bpf_prog_put_deferred().  For the record, no one can determine, or
remember, why it was necessary to free the program ID, and remove it
from the IDR, prior to executing bpf_prog_put_deferred();
regardless, both Stanislav and Alexei agree that the approach in this
patch should be safe.

It is worth noting that when moving the bpf_prog_free_id() call, the
do_idr_lock parameter was forced to true as the ebpf devs determined
this was the correct as the do_idr_lock should always be true.  The
do_idr_lock parameter will be removed in a follow-up patch, but it
was kept here to keep the patch small in an effort to ease any stable
backports.

I also modified the bpf_audit_prog() logic used to associate the
AUDIT_BPF record with other associated records, e.g. @ctx != NULL.
Instead of keying off the operation, it now keys off the execution
context, e.g. '!in_irg && !irqs_disabled()', which is much more
appropriate and should help better connect the UNLOAD operations with
the associated audit state (other audit records).

Cc: stable at vger.kernel.org
Fixes: d809e134be7a ("bpf: Prepare bpf_prog_put() to be called from irq context.")
Reported-by: Burn Alting <burn.alting at iinet.net.au>
Reported-by: Jiri Olsa <olsajiri at gmail.com>
Suggested-by: Stanislav Fomichev <sdf at google.com>
Suggested-by: Alexei Starovoitov <alexei.starovoitov at gmail.com>
Signed-off-by: Paul Moore <paul at paul-moore.com>

---
* v3
- abandon most of the changes in v2
- move bpf_prog_free_id() after the audit/perf unload hooks
- remove bpf_prog_free_id() from __bpf_prog_offload_destroy()
- added stable tag
* v2
- change subj
- add mention of the perf regression
- drop the dedicated program audit ID
- add the bpf_prog::valid_id flag, bpf_prog_get_id() getter
- convert prog ID users to new ID getter
* v1
- subj was: "bpf: restore the ebpf audit UNLOAD id field"
- initial draft
---
 kernel/bpf/offload.c | 3 ---
 kernel/bpf/syscall.c | 6 ++----
 2 files changed, 2 insertions(+), 7 deletions(-)

diff --git a/kernel/bpf/offload.c b/kernel/bpf/offload.c
index 13e4efc971e6..190d9f9dc987 100644
--- a/kernel/bpf/offload.c
+++ b/kernel/bpf/offload.c
@@ -216,9 +216,6 @@ static void __bpf_prog_offload_destroy(struct bpf_prog *prog)
 	if (offload->dev_state)
 		offload->offdev->ops->destroy(prog);
 
-	/* Make sure BPF_PROG_GET_NEXT_ID can't find this dead program */
-	bpf_prog_free_id(prog, true);
-
 	list_del_init(&offload->offloads);
 	kfree(offload);
 	prog->aux->offload = NULL;
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 64131f88c553..61bb19e81b9c 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -1972,7 +1972,7 @@ static void bpf_audit_prog(const struct bpf_prog *prog, unsigned int op)
 		return;
 	if (audit_enabled == AUDIT_OFF)
 		return;
-	if (op == BPF_AUDIT_LOAD)
+	if (!in_irq() && !irqs_disabled())
 		ctx = audit_context();
 	ab = audit_log_start(ctx, GFP_ATOMIC, AUDIT_BPF);
 	if (unlikely(!ab))
@@ -2067,6 +2067,7 @@ static void bpf_prog_put_deferred(struct work_struct *work)
 	prog = aux->prog;
 	perf_event_bpf_event(prog, PERF_BPF_EVENT_PROG_UNLOAD, 0);
 	bpf_audit_prog(prog, BPF_AUDIT_UNLOAD);
+	bpf_prog_free_id(prog, true);
 	__bpf_prog_put_noref(prog, true);
 }
 
@@ -2075,9 +2076,6 @@ static void __bpf_prog_put(struct bpf_prog *prog, bool do_idr_lock)
 	struct bpf_prog_aux *aux = prog->aux;
 
 	if (atomic64_dec_and_test(&aux->refcnt)) {
-		/* bpf_prog_free_id() must be called first */
-		bpf_prog_free_id(prog, do_idr_lock);
-
 		if (in_irq() || irqs_disabled()) {
 			INIT_WORK(&aux->work, bpf_prog_put_deferred);
 			schedule_work(&aux->work);
-- 
2.39.0