bpf: Sanitize the bpf_struct_ops tcp-cc name

The bpf_struct_ops tcp-cc name should be sanitized in order to
avoid problematic chars (e.g. whitespaces).

This patch reuses the bpf_obj_name_cpy() for accepting the same set
of characters in order to keep a consistent bpf programming experience.
A "size" param is added.  Also, the strlen is returned on success so
that the caller (like the bpf_tcp_ca here) can error out on empty name.
The existing callers of the bpf_obj_name_cpy() only need to change the
testing statement to "if (err < 0)".  For all these existing callers,
the err will be overwritten later, so no extra change is needed
for the new strlen return value.

v3:
  - reverse xmas tree style
v2:
  - Save the orig_src to avoid "end - size" (Andrii)

Fixes: 0baf26b0 ("bpf: tcp: Support tcp_congestion_ops in bpf")
Signed-off-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Link: https://lore.kernel.org/bpf/20200314010209.1131542-1-kafai@fb.com

include/linux/bpf.h

@@ -160,6 +160,7 @@ static inline void copy_map_value(struct bpf_map *map, void *dst, void *src)
 }
 void copy_map_value_locked(struct bpf_map *map, void *dst, void *src,
 			   bool lock_src);
+int bpf_obj_name_cpy(char *dst, const char *src, unsigned int size);
 
 struct bpf_offload_dev;
 struct bpf_offloaded_map;

kernel/bpf/syscall.c

@@ -696,14 +696,15 @@ int bpf_get_file_flag(int flags)
 		   offsetof(union bpf_attr, CMD##_LAST_FIELD) - \
 		   sizeof(attr->CMD##_LAST_FIELD)) != NULL
 
-/* dst and src must have at least BPF_OBJ_NAME_LEN number of bytes.
- * Return 0 on success and < 0 on error.
+/* dst and src must have at least "size" number of bytes.
+ * Return strlen on success and < 0 on error.
  */
-static int bpf_obj_name_cpy(char *dst, const char *src)
+int bpf_obj_name_cpy(char *dst, const char *src, unsigned int size)
 {
-	const char *end = src + BPF_OBJ_NAME_LEN;
+	const char *end = src + size;
+	const char *orig_src = src;
 
-	memset(dst, 0, BPF_OBJ_NAME_LEN);
+	memset(dst, 0, size);
 	/* Copy all isalnum(), '_' and '.' chars. */
 	while (src < end && *src) {
 		if (!isalnum(*src) &&
@@ -712,11 +713,11 @@ static int bpf_obj_name_cpy(char *dst, const char *src)
 		*dst++ = *src++;
 	}
 
-	/* No '\0' found in BPF_OBJ_NAME_LEN number of bytes */
+	/* No '\0' found in "size" number of bytes */
 	if (src == end)
 		return -EINVAL;
 
-	return 0;
+	return src - orig_src;
 }
 
 int map_check_no_btf(const struct bpf_map *map,
@@ -810,8 +811,9 @@ static int map_create(union bpf_attr *attr)
 	if (IS_ERR(map))
 		return PTR_ERR(map);
 
-	err = bpf_obj_name_cpy(map->name, attr->map_name);
-	if (err)
+	err = bpf_obj_name_cpy(map->name, attr->map_name,
+			       sizeof(attr->map_name));
+	if (err < 0)
 		goto free_map;
 
 	atomic64_set(&map->refcnt, 1);
@@ -2098,8 +2100,9 @@ static int bpf_prog_load(union bpf_attr *attr, union bpf_attr __user *uattr)
 		goto free_prog;
 
 	prog->aux->load_time = ktime_get_boottime_ns();
-	err = bpf_obj_name_cpy(prog->aux->name, attr->prog_name);
-	if (err)
+	err = bpf_obj_name_cpy(prog->aux->name, attr->prog_name,
+			       sizeof(attr->prog_name));
+	if (err < 0)
 		goto free_prog;
 
 	/* run eBPF verifier */

net/ipv4/bpf_tcp_ca.c

@@ -184,7 +184,6 @@ static int bpf_tcp_ca_init_member(const struct btf_type *t,
 {
 	const struct tcp_congestion_ops *utcp_ca;
 	struct tcp_congestion_ops *tcp_ca;
-	size_t tcp_ca_name_len;
 	int prog_fd;
 	u32 moff;
 
@@ -199,13 +198,11 @@ static int bpf_tcp_ca_init_member(const struct btf_type *t,
 		tcp_ca->flags = utcp_ca->flags;
 		return 1;
 	case offsetof(struct tcp_congestion_ops, name):
-		tcp_ca_name_len = strnlen(utcp_ca->name, sizeof(utcp_ca->name));
-		if (!tcp_ca_name_len ||
-		    tcp_ca_name_len == sizeof(utcp_ca->name))
+		if (bpf_obj_name_cpy(tcp_ca->name, utcp_ca->name,
+				     sizeof(tcp_ca->name)) <= 0)
 			return -EINVAL;
 		if (tcp_ca_find(utcp_ca->name))
 			return -EEXIST;
-		memcpy(tcp_ca->name, utcp_ca->name, sizeof(tcp_ca->name));
 		return 1;
 	}