From: Stanislav Fomichev <sdf@google.com>
Date: Wed, 25 Mar 2020 12:55:21 -0700
Subject: libbpf: Don't allocate 16M for log buffer by default
Patch-mainline: v5.7-rc1
Git-commit: 8395f320b407509819cc112f61a1de05780c8cba
References: bsc#1177028

For each prog/btf load we allocate and free 16 megs of verifier buffer.
On production systems it doesn't really make sense because the
programs/btf have gone through extensive testing and (mostly) guaranteed
to successfully load.

Let's assume successful case by default and skip buffer allocation
on the first try. If there is an error, start with BPF_LOG_BUF_SIZE
and double it on each ENOSPC iteration.

v3:
* Return -ENOMEM when can't allocate log buffer (Andrii Nakryiko)

v2:
* Don't allocate the buffer at all on the first try (Andrii Nakryiko)

Signed-off-by: Stanislav Fomichev <sdf@google.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Link: https://lore.kernel.org/bpf/20200325195521.112210-1-sdf@google.com
Acked-by: Gary Lin <glin@suse.com>
---
 tools/lib/bpf/btf.c    |   20 +++++++++++++++-----
 tools/lib/bpf/libbpf.c |   22 ++++++++++++++--------
 2 files changed, 29 insertions(+), 13 deletions(-)

--- a/tools/lib/bpf/btf.c
+++ b/tools/lib/bpf/btf.c
@@ -657,22 +657,32 @@ int btf__finalize_data(struct bpf_object
 
 int btf__load(struct btf *btf)
 {
-	__u32 log_buf_size = BPF_LOG_BUF_SIZE;
+	__u32 log_buf_size = 0;
 	char *log_buf = NULL;
 	int err = 0;
 
 	if (btf->fd >= 0)
 		return -EEXIST;
 
-	log_buf = malloc(log_buf_size);
-	if (!log_buf)
-		return -ENOMEM;
+retry_load:
+	if (log_buf_size) {
+		log_buf = malloc(log_buf_size);
+		if (!log_buf)
+			return -ENOMEM;
 
-	*log_buf = 0;
+		*log_buf = 0;
+	}
 
 	btf->fd = bpf_load_btf(btf->data, btf->data_size,
 			       log_buf, log_buf_size, false);
 	if (btf->fd < 0) {
+		if (!log_buf || errno == ENOSPC) {
+			log_buf_size = max((__u32)BPF_LOG_BUF_SIZE,
+					   log_buf_size << 1);
+			free(log_buf);
+			goto retry_load;
+		}
+
 		err = -errno;
 		pr_warning("Error loading BTF: %s(%d)\n", strerror(errno), errno);
 		if (*log_buf)
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -4853,8 +4853,8 @@ load_program(struct bpf_program *prog, s
 {
 	struct bpf_load_program_attr load_attr;
 	char *cp, errmsg[STRERR_BUFSIZE];
-	int log_buf_size = BPF_LOG_BUF_SIZE;
-	char *log_buf;
+	size_t log_buf_size = 0;
+	char *log_buf = NULL;
 	int btf_fd, ret;
 
 	if (!insns || !insns_cnt)
@@ -4894,22 +4894,28 @@ load_program(struct bpf_program *prog, s
 	load_attr.prog_flags = prog->prog_flags;
 
 retry_load:
-	log_buf = malloc(log_buf_size);
-	if (!log_buf)
-		pr_warning("Alloc log buffer for bpf loader error, continue without log\n");
+	if (log_buf_size) {
+		log_buf = malloc(log_buf_size);
+		if (!log_buf)
+			return -ENOMEM;
+
+		*log_buf = 0;
+	}
 
 	ret = bpf_load_program_xattr(&load_attr, log_buf, log_buf_size);
 
 	if (ret >= 0) {
-		if (load_attr.log_level)
+		if (log_buf && load_attr.log_level)
 			pr_debug("verifier log:\n%s", log_buf);
 		*pfd = ret;
 		ret = 0;
 		goto out;
 	}
 
-	if (errno == ENOSPC) {
-		log_buf_size <<= 1;
+	if (!log_buf || errno == ENOSPC) {
+		log_buf_size = max((size_t)BPF_LOG_BUF_SIZE,
+				   log_buf_size << 1);
+
 		free(log_buf);
 		goto retry_load;
 	}