Replace the deprecated[1] strncpy() with strnlen() on the source followed by memcpy(). Normally strscpy() would be used in this case, but skel_internal.h is shared between kernel and userspace tools, and strscpy() is not available in the userspace build context.
The source map_name is a NUL-terminated C string (the only caller passes a 12 character string literal). The destination attr.map_name is char[BPF_OBJ_NAME_LEN] (16 bytes) in union bpf_attr, passed to the bpf() syscall. The kernel's bpf_obj_name_cpy() requires a NUL terminator within the 16-byte field, rejecting names that use all 16 bytes. Valid names are therefore at most 15 characters. The attr is pre-zeroed with memset() at the top of the function, so the byte at position 15 is always NUL. The copy is bounded to sizeof(attr.map_name) - 1 (15 bytes) to guarantee NUL-termination is preserved. This is safe because the kernel would reject a 16-byte unterminated name anyway, and the only in-tree caller passes "__loader.map" (12 characters). While the original strncpy() would have copied a full 16 bytes from an overlong name (producing an unterminated field that the syscall rejects), but this shouldn't be a reachable state. Forcing truncation to 15 bytes, however, seemed to induce a (unrelated?) BPF selftest failure: https://github.com/kernel-patches/bpf/actions/runs/23472955268/job/68300440546 Allow the literal to exceed 15 characters and exactly reproduce the original strncpy() behavior (potentially lacking a NUL termination). Link: https://github.com/KSPP/linux/issues/90 [1] Signed-off-by: Kees Cook <[email protected]> --- v2: don't force truncation v1: https://lore.kernel.org/lkml/[email protected]/ Cc: Andrii Nakryiko <[email protected]> Cc: Eduard Zingerman <[email protected]> Cc: Alexei Starovoitov <[email protected]> Cc: Daniel Borkmann <[email protected]> Cc: Martin KaFai Lau <[email protected]> Cc: Song Liu <[email protected]> Cc: Yonghong Song <[email protected]> Cc: John Fastabend <[email protected]> Cc: KP Singh <[email protected]> Cc: Stanislav Fomichev <[email protected]> Cc: Hao Luo <[email protected]> Cc: Jiri Olsa <[email protected]> Cc: <[email protected]> --- tools/lib/bpf/skel_internal.h | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/tools/lib/bpf/skel_internal.h b/tools/lib/bpf/skel_internal.h index 6a8f5c7a02eb..8702d6612978 100644 --- a/tools/lib/bpf/skel_internal.h +++ b/tools/lib/bpf/skel_internal.h @@ -243,7 +243,8 @@ static inline int skel_map_create(enum bpf_map_type map_type, attr.excl_prog_hash = (unsigned long) excl_prog_hash; attr.excl_prog_hash_size = excl_prog_hash_sz; - strncpy(attr.map_name, map_name, sizeof(attr.map_name)); + memcpy(attr.map_name, map_name, + strnlen(map_name, sizeof(attr.map_name))); attr.key_size = key_size; attr.value_size = value_size; attr.max_entries = max_entries; -- 2.34.1
