netdev - [PATCH bpf] libbpf: Prevent overriding errno when logging errors

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Date:   Thu, 13 Aug 2020 16:29:05 +0200
From:   Toke Høiland-Jørgensen <toke@...hat.com>
To:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>
Cc:     Toke Høiland-Jørgensen <toke@...hat.com>,
        netdev@...r.kernel.org, bpf@...r.kernel.org
Subject: [PATCH bpf] libbpf: Prevent overriding errno when logging errors

Turns out there were a few more instances where libbpf didn't save the
errno before writing an error message, causing errno to be overridden by
the printf() return and the error disappearing if logging is enabled.

Signed-off-by: Toke Høiland-Jørgensen <toke@...hat.com>
---
 tools/lib/bpf/libbpf.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 0a06124f7999..fd256440e233 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -3478,10 +3478,11 @@ bpf_object__probe_global_data(struct bpf_object *obj)
 
 	map = bpf_create_map_xattr(&map_attr);
 	if (map < 0) {
-		cp = libbpf_strerror_r(errno, errmsg, sizeof(errmsg));
+		ret = -errno;
+		cp = libbpf_strerror_r(-ret, errmsg, sizeof(errmsg));
 		pr_warn("Error in %s():%s(%d). Couldn't create simple array map.\n",
-			__func__, cp, errno);
-		return -errno;
+			__func__, cp, -ret);
+		return ret;
 	}
 
 	insns[0].imm = map;
@@ -6012,9 +6013,10 @@ int bpf_program__pin_instance(struct bpf_program *prog, const char *path,
 	}
 
 	if (bpf_obj_pin(prog->instances.fds[instance], path)) {
-		cp = libbpf_strerror_r(errno, errmsg, sizeof(errmsg));
+		err = -errno;
+		cp = libbpf_strerror_r(-err, errmsg, sizeof(errmsg));
 		pr_warn("failed to pin program: %s\n", cp);
-		return -errno;
+		return err;
 	}
 	pr_debug("pinned program '%s'\n", path);
 
-- 
2.28.0