[PATCH] bpf: restore the ebpf audit UNLOAD id field

[Paul Moore <paul@paul-moore.com>]

When changing the ebpf program put() routines to support being called
from within IRQ context the program ID was reset to zero prior to
generating the audit UNLOAD record, which obviously rendered the ID
field bogus (always zero).  This patch resolves this by adding a new
field, bpf_prog_aux::id_audit, which is set when the ebpf program is
allocated an ID and never reset, ensuring a valid ID field,
regardless of the state of the original ID field, bpf_prox_aud::id.

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).

As an note to future bug hunters, I did briefly consider removing the
ID reset in bpf_prog_free_id(), as it would seem that once the
program is removed from the idr pool it can no longer be found by its
ID value, but commit ad8ad79f4f60 ("bpf: offload: free program id
when device disappears") seems to imply that it is beneficial to
reset the ID value.  Perhaps as a secondary indicator that the ebpf
program is unbound/orphaned.

Fixes: d809e134be7a ("bpf: Prepare bpf_prog_put() to be called from irq context.")
Reported-by: Burn Alting <burn.alting@iinet.net.au>
Signed-off-by: Paul Moore <paul@paul-moore.com>
---
 include/linux/bpf.h  | 1 +
 kernel/bpf/syscall.c | 8 +++++---
 2 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 9e7d46d16032..a22001ceb2c3 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -1103,6 +1103,7 @@ struct bpf_prog_aux {
 	u32 max_tp_access;
 	u32 stack_depth;
 	u32 id;
+	u32 id_audit; /* preserves the id for use by audit */
 	u32 func_cnt; /* used by non-func prog as the number of func progs */
 	u32 func_idx; /* 0 for non-func prog, the index in func array for func prog */
 	u32 attach_btf_id; /* in-kernel BTF type id to attach to */
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 7b373a5e861f..3ec09f4dba18 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -1958,13 +1958,13 @@ 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))
 		return;
 	audit_log_format(ab, "prog-id=%u op=%s",
-			 prog->aux->id, bpf_audit_str[op]);
+			 prog->aux->id_audit, bpf_audit_str[op]);
 	audit_log_end(ab);
 }
 
@@ -1975,8 +1975,10 @@ static int bpf_prog_alloc_id(struct bpf_prog *prog)
 	idr_preload(GFP_KERNEL);
 	spin_lock_bh(&prog_idr_lock);
 	id = idr_alloc_cyclic(&prog_idr, prog, 1, INT_MAX, GFP_ATOMIC);
-	if (id > 0)
+	if (id > 0) {
 		prog->aux->id = id;
+		prog->aux->id_audit = id;
+	}
 	spin_unlock_bh(&prog_idr_lock);
 	idr_preload_end();
 
-- 
2.39.0