netdev - [PATCH bpf-next] [tools/bpf] fix a few ubsan warning

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Date:   Tue, 9 Apr 2019 17:37:41 -0700
From:   Yonghong Song <yhs@...com>
To:     <bpf@...r.kernel.org>, <netdev@...r.kernel.org>
CC:     Alexei Starovoitov <ast@...com>,
        Daniel Borkmann <daniel@...earbox.net>, <kernel-team@...com>,
        Yonghong Song <yhs@...com>
Subject: [PATCH bpf-next] [tools/bpf] fix a few ubsan warning

The issue is reported at https://github.com/libbpf/libbpf/issues/28.

Basically, per C standard, for
  void *memcpy(void *dest, const void *src, size_t n)
if "dest" or "src" is NULL, regardless of whether "n" is 0 or not,
the result of memcpy is undefined. clang ubsan reported three such
instances in bpf.c with the following pattern:
  memcpy(dest, 0, 0).

Although in practice, no known compiler will cause issues when
copy size is 0. Let us still fix the issue to silence ubsan
warnings.

Signed-off-by: Yonghong Song <yhs@...com>
---
 tools/lib/bpf/bpf.c | 19 +++++++++----------
 1 file changed, 9 insertions(+), 10 deletions(-)

diff --git a/tools/lib/bpf/bpf.c b/tools/lib/bpf/bpf.c
index a1db869a6fda..78f2400dd2d1 100644
--- a/tools/lib/bpf/bpf.c
+++ b/tools/lib/bpf/bpf.c
@@ -79,7 +79,6 @@ static inline int sys_bpf_prog_load(union bpf_attr *attr, unsigned int size)
 
 int bpf_create_map_xattr(const struct bpf_create_map_attr *create_attr)
 {
-	__u32 name_len = create_attr->name ? strlen(create_attr->name) : 0;
 	union bpf_attr attr;
 
 	memset(&attr, '\0', sizeof(attr));
@@ -89,8 +88,9 @@ int bpf_create_map_xattr(const struct bpf_create_map_attr *create_attr)
 	attr.value_size = create_attr->value_size;
 	attr.max_entries = create_attr->max_entries;
 	attr.map_flags = create_attr->map_flags;
-	memcpy(attr.map_name, create_attr->name,
-	       min(name_len, BPF_OBJ_NAME_LEN - 1));
+	if (create_attr->name)
+		memcpy(attr.map_name, create_attr->name,
+		       min(strlen(create_attr->name), BPF_OBJ_NAME_LEN - 1));
 	attr.numa_node = create_attr->numa_node;
 	attr.btf_fd = create_attr->btf_fd;
 	attr.btf_key_type_id = create_attr->btf_key_type_id;
@@ -155,7 +155,6 @@ int bpf_create_map_in_map_node(enum bpf_map_type map_type, const char *name,
 			       int key_size, int inner_map_fd, int max_entries,
 			       __u32 map_flags, int node)
 {
-	__u32 name_len = name ? strlen(name) : 0;
 	union bpf_attr attr;
 
 	memset(&attr, '\0', sizeof(attr));
@@ -166,7 +165,9 @@ int bpf_create_map_in_map_node(enum bpf_map_type map_type, const char *name,
 	attr.inner_map_fd = inner_map_fd;
 	attr.max_entries = max_entries;
 	attr.map_flags = map_flags;
-	memcpy(attr.map_name, name, min(name_len, BPF_OBJ_NAME_LEN - 1));
+	if (name)
+		memcpy(attr.map_name, name,
+		       min(strlen(name), BPF_OBJ_NAME_LEN - 1));
 
 	if (node >= 0) {
 		attr.map_flags |= BPF_F_NUMA_NODE;
@@ -216,7 +217,6 @@ int bpf_load_program_xattr(const struct bpf_load_program_attr *load_attr,
 	void *finfo = NULL, *linfo = NULL;
 	union bpf_attr attr;
 	__u32 log_level;
-	__u32 name_len;
 	int fd;
 
 	if (!load_attr || !log_buf != !log_buf_sz)
@@ -226,8 +226,6 @@ int bpf_load_program_xattr(const struct bpf_load_program_attr *load_attr,
 	if (log_level > (4 | 2 | 1) || (log_level && !log_buf))
 		return -EINVAL;
 
-	name_len = load_attr->name ? strlen(load_attr->name) : 0;
-
 	memset(&attr, 0, sizeof(attr));
 	attr.prog_type = load_attr->prog_type;
 	attr.expected_attach_type = load_attr->expected_attach_type;
@@ -253,8 +251,9 @@ int bpf_load_program_xattr(const struct bpf_load_program_attr *load_attr,
 	attr.line_info_rec_size = load_attr->line_info_rec_size;
 	attr.line_info_cnt = load_attr->line_info_cnt;
 	attr.line_info = ptr_to_u64(load_attr->line_info);
-	memcpy(attr.prog_name, load_attr->name,
-	       min(name_len, BPF_OBJ_NAME_LEN - 1));
+	if (load_attr->name)
+		memcpy(attr.prog_name, load_attr->name,
+		       min(strlen(load_attr->name), BPF_OBJ_NAME_LEN - 1));
 
 	fd = sys_bpf_prog_load(&attr, sizeof(attr));
 	if (fd >= 0)
-- 
2.17.1