netdev - [PATCH bpf-next 3/6] libbpf: Propagate EPERM to caller on program load

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Message-ID: <157314554141.693412.14085088717794768890.stgit@toke.dk>
Date:   Thu, 07 Nov 2019 17:52:21 +0100
From:   Toke Høiland-Jørgensen <toke@...hat.com>
To:     Daniel Borkmann <daniel@...earbox.net>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Andrii Nakryiko <andrii.nakryiko@...il.com>,
        David Miller <davem@...emloft.net>, netdev@...r.kernel.org,
        bpf@...r.kernel.org
Subject: [PATCH bpf-next 3/6] libbpf: Propagate EPERM to caller on program
 load

From: Toke Høiland-Jørgensen <toke@...hat.com>

When loading an eBPF program, libbpf overrides the return code for EPERM
errors instead of returning it to the caller. This makes it hard to figure
out what went wrong on load.

In particular, EPERM is returned when the system rlimit is too low to lock
the memory required for the BPF program. Previously, this was somewhat
obscured because the rlimit error would be hit on map creation (which does
return it correctly). However, sine maps can now be reused, object load can
proceed all the way to loading programs without hitting the error;
propagating it even in this case makes it possible for the caller to react
appropriately (and, e.g., attempt to raise the rlimit before retrying).

Signed-off-by: Toke Høiland-Jørgensen <toke@...hat.com>
---
 tools/lib/bpf/libbpf.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index cea61b2ec9d3..582c0fd16697 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -3721,7 +3721,7 @@ load_program(struct bpf_program *prog, struct bpf_insn *insns, int insns_cnt,
 		free(log_buf);
 		goto retry_load;
 	}
-	ret = -LIBBPF_ERRNO__LOAD;
+	ret = (errno == EPERM) ? -errno : -LIBBPF_ERRNO__LOAD;
 	cp = libbpf_strerror_r(errno, errmsg, sizeof(errmsg));
 	pr_warn("load bpf program failed: %s\n", cp);

@@ -3749,7 +3749,7 @@ load_program(struct bpf_program *prog, struct bpf_insn *insns, int insns_cnt,
 			}
 		}

-		if (log_buf)
+		if (log_buf && ret != -EPERM)
 			ret = -LIBBPF_ERRNO__KVER;
 	}