File 0038-bpf-program-make-bpf_program_load_kernel-i... of Package systemd

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File 0038-bpf-program-make-bpf_program_load_kernel-idempotent.patch of Package systemd (Revision a47769d8fb254159c07462a5675e1695)

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From f609216b09652bfdbc5e25f63b3cd95db08ef4a2 Mon Sep 17 00:00:00 2001
From: Lennart Poettering <lennart@poettering.net>
Date: Tue, 20 Feb 2018 19:19:57 +0100
Subject: [PATCH 38/51] bpf-program: make bpf_program_load_kernel() idempotent

Let's "seal" off the BPF program as soo as bpf_program_load_kernel() is
called, which allows us to make it idempotent: since the program can't
be modified anymore after being turned into a kernel object it's safe to
shortcut behaviour if called multiple times.

(cherry picked from commit e0ad39fc52ed851974dd8f522a45a2539b524bed)
---
 src/basic/bpf-program.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/src/basic/bpf-program.c b/src/basic/bpf-program.c
index 8f59ebd958..133ffe1798 100644
--- a/src/basic/bpf-program.c
+++ b/src/basic/bpf-program.c
@@ -27,6 +27,7 @@
 #include "fd-util.h"
 #include "log.h"
 #include "missing.h"
+#include "util.h"
 
 int bpf_program_new(uint32_t prog_type, BPFProgram **ret) {
         _cleanup_(bpf_program_unrefp) BPFProgram *p = NULL;
@@ -57,6 +58,9 @@ int bpf_program_add_instructions(BPFProgram *p, const struct bpf_insn *instructi
 
         assert(p);
 
+        if (p->kernel_fd >= 0) /* don't allow modification after we uploaded things to the kernel */
+                return -EBUSY;
+
         if (!GREEDY_REALLOC(p->instructions, p->allocated, p->n_instructions + count))
                 return -ENOMEM;
 
@@ -71,8 +75,10 @@ int bpf_program_load_kernel(BPFProgram *p, char *log_buf, size_t log_size) {
 
         assert(p);
 
-        if (p->kernel_fd >= 0)
-                return -EBUSY;
+        if (p->kernel_fd >= 0) { /* make this idempotent */
+                memzero(log_buf, log_size);
+                return 0;
+        }
 
         attr = (union bpf_attr) {
                 .prog_type = p->prog_type,
-- 
2.16.4

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File 0038-bpf-program-make-bpf_program_load_kernel-idempotent.patch of Package systemd (Revision a47769d8fb254159c07462a5675e1695)

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