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libbpf: Add sane strncpy alternative and use it internally

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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: 2f6324a3937f8 (libbpf: Support shared umems between queues and devices)
Reported-by: Emmanuel Deloget <emmanuel.deloget@eho.link>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20211211004043.2374068-1-andrii@kernel.org
This commit is contained in:
Andrii Nakryiko
2021-12-10 16:40:43 -08:00
committed by Andrii Nakryiko
parent df5689f1c8
commit a4e725f8f5
6 changed files with 31 additions and 19 deletions
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8
src/libbpf.c
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@@ -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;
}