Commit 9fc205b4 authored by Andrii Nakryiko's avatar Andrii Nakryiko Committed by Daniel Borkmann
Browse files

libbpf: Add sane strncpy alternative and use it internally 



strncpy() has a notoriously error-prone semantics which makes GCC
complain about it a lot (and quite often completely completely falsely
at that). Instead of pleasing GCC all the time (-Wno-stringop-truncation
is unfortunately only supported by GCC, so it's a bit too messy to just
enable it in Makefile), add libbpf-internal libbpf_strlcpy() helper
which follows what FreeBSD's strlcpy() does and what most people would
expect from strncpy(): copies up to N-1 first bytes from source string
into destination string and ensures zero-termination afterwards.

Replace all the relevant uses of strncpy/strncat/memcpy in libbpf with
libbpf_strlcpy().

This also fixes the issue reported by Emmanuel Deloget in xsk.c where
memcpy() could access source string beyond its end.

Fixes: 2f6324a3 (libbpf: Support shared umems between queues and devices)
Reported-by: default avatarEmmanuel Deloget <emmanuel.deloget@eho.link>
Signed-off-by: default avatarAndrii Nakryiko <andrii@kernel.org>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20211211004043.2374068-1-andrii@kernel.org
parent 4581e676

tools/lib/bpf/bpf.c

+2 −2
Original line number Diff line number Diff line
@@ -112,7 +112,7 @@ int bpf_map_create(enum bpf_map_type map_type, 


	attr.map_type = map_type;

	if (map_name)

		strncat(attr.map_name, map_name, sizeof(attr.map_name) - 1);

		libbpf_strlcpy(attr.map_name, map_name, sizeof(attr.map_name));

	attr.key_size = key_size;

	attr.value_size = value_size;

	attr.max_entries = max_entries;
@@ -271,7 +271,7 @@ int bpf_prog_load_v0_6_0(enum bpf_prog_type prog_type, 
	attr.kern_version = OPTS_GET(opts, kern_version, 0);



	if (prog_name)

		strncat(attr.prog_name, prog_name, sizeof(attr.prog_name) - 1);

		libbpf_strlcpy(attr.prog_name, prog_name, sizeof(attr.prog_name));

	attr.license = ptr_to_u64(license);



	if (insn_cnt > UINT_MAX)

tools/lib/bpf/btf_dump.c

+2 −2
Original line number Diff line number Diff line
@@ -2321,8 +2321,8 @@ int btf_dump__dump_type_data(struct btf_dump *d, __u32 id, 
	if (!opts->indent_str)

		d->typed_dump->indent_str[0] = '\t';

	else

		strncat(d->typed_dump->indent_str, opts->indent_str,

			sizeof(d->typed_dump->indent_str) - 1);

		libbpf_strlcpy(d->typed_dump->indent_str, opts->indent_str,

			       sizeof(d->typed_dump->indent_str));



	d->typed_dump->compact = OPTS_GET(opts, compact, false);

	d->typed_dump->skip_names = OPTS_GET(opts, skip_names, false);

tools/lib/bpf/gen_loader.c

+2 −4
Original line number Diff line number Diff line
@@ -463,8 +463,7 @@ void bpf_gen__map_create(struct bpf_gen *gen, 
	attr.map_flags = map_attr->map_flags;

	attr.map_extra = map_attr->map_extra;

	if (map_name)

		memcpy(attr.map_name, map_name,

		       min((unsigned)strlen(map_name), BPF_OBJ_NAME_LEN - 1));

		libbpf_strlcpy(attr.map_name, map_name, sizeof(attr.map_name));

	attr.numa_node = map_attr->numa_node;

	attr.map_ifindex = map_attr->map_ifindex;

	attr.max_entries = max_entries;
@@ -970,8 +969,7 @@ void bpf_gen__prog_load(struct bpf_gen *gen, 
	core_relos = add_data(gen, gen->core_relos,

			     attr.core_relo_cnt * attr.core_relo_rec_size);



	memcpy(attr.prog_name, prog_name,

	       min((unsigned)strlen(prog_name), BPF_OBJ_NAME_LEN - 1));

	libbpf_strlcpy(attr.prog_name, prog_name, sizeof(attr.prog_name));

	prog_load_attr = add_data(gen, &attr, attr_size);



	/* populate union bpf_attr with a pointer to license */

tools/lib/bpf/libbpf.c

+3 −5
Original line number Diff line number Diff line
@@ -1201,12 +1201,10 @@ static struct bpf_object *bpf_object__new(const char *path, 


	strcpy(obj->path, path);

	if (obj_name) {

		strncpy(obj->name, obj_name, sizeof(obj->name) - 1);

		obj->name[sizeof(obj->name) - 1] = 0;

		libbpf_strlcpy(obj->name, obj_name, sizeof(obj->name));

	} else {

		/* Using basename() GNU version which doesn't modify arg. */

		strncpy(obj->name, basename((void *)path),

			sizeof(obj->name) - 1);

		libbpf_strlcpy(obj->name, basename((void *)path), sizeof(obj->name));

		end = strchr(obj->name, '.');

		if (end)

			*end = 0;
@@ -1358,7 +1356,7 @@ static int bpf_object__check_endianness(struct bpf_object *obj) 
static int

bpf_object__init_license(struct bpf_object *obj, void *data, size_t size)

{

	memcpy(obj->license, data, min(size, sizeof(obj->license) - 1));

	libbpf_strlcpy(obj->license, data, sizeof(obj->license));

	pr_debug("license of %s is %s\n", obj->path, obj->license);

	return 0;

}

tools/lib/bpf/libbpf_internal.h

+19 −0
Original line number Diff line number Diff line
@@ -169,6 +169,25 @@ static inline void *libbpf_reallocarray(void *ptr, size_t nmemb, size_t size) 
	return realloc(ptr, total);

}



/* Copy up to sz - 1 bytes from zero-terminated src string and ensure that dst

 * is zero-terminated string no matter what (unless sz == 0, in which case

 * it's a no-op). It's conceptually close to FreeBSD's strlcpy(), but differs

 * in what is returned. Given this is internal helper, it's trivial to extend

 * this, when necessary. Use this instead of strncpy inside libbpf source code.

 */

static inline void libbpf_strlcpy(char *dst, const char *src, size_t sz)

{

	size_t i;



	if (sz == 0)

		return;



	sz--;

	for (i = 0; i < sz && src[i]; i++)

		dst[i] = src[i];

	dst[i] = '\0';

}



struct btf;

struct btf_type;