On 2024-04-03 at 05:22:50, Justin Stitt ([email protected]) wrote:
> strncpy() is deprecated for use on NUL-terminated destination strings
> [1] and as such we should prefer more robust and less ambiguous string
> interfaces.
>
> bpf sym names get looked up and compared/cleaned with various string
> apis. This suggests they need to be NUL-terminated (strncpy() suggests
> this but does not guarantee it).
>
> | static int compare_symbol_name(const char *name, char *namebuf)
> | {
> | cleanup_symbol_name(namebuf);
> | return strcmp(name, namebuf);
> | }
>
> | static void cleanup_symbol_name(char *s)
> | {
> | ...
> | res = strstr(s, ".llvm.");
> | ...
> | }
>
> Use strscpy() as this method guarantees NUL-termination on the
> destination buffer.
>
> This patch also replaces two uses of strncpy() used in log.c. These are
> simple replacements as postfix has been zero-initialized on the stack
> and has source arguments with a size less than the destination's size.
>
> Note that this patch uses the new 2-argument version of strscpy
> introduced in Commit e6584c3964f2f ("string: Allow 2-argument
> strscpy()").
>
> Link:
> https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings
> [1]
> Link: https://manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html
> [2]
> Link: https://github.com/KSPP/linux/issues/90
> Cc: [email protected]
> Signed-off-by: Justin Stitt <[email protected]>
> ---
> Note: build-tested only.
>
> Found with: $ rg "strncpy\("
> ---
> kernel/bpf/core.c | 4 ++--
> kernel/bpf/log.c | 4 ++--
> 2 files changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
> index 696bc55de8e8..8c9078f4549c 100644
> --- a/kernel/bpf/core.c
> +++ b/kernel/bpf/core.c
> @@ -747,7 +747,7 @@ const char *__bpf_address_lookup(unsigned long addr,
> unsigned long *size,
> unsigned long symbol_start = ksym->start;
> unsigned long symbol_end = ksym->end;
>
> - strncpy(sym, ksym->name, KSYM_NAME_LEN);
> + strscpy(sym, ksym->name, KSYM_NAME_LEN);
You dont have to check return value of strscpy for errors ?
>
> ret = sym;
> if (size)
> @@ -813,7 +813,7 @@ int bpf_get_kallsym(unsigned int symnum, unsigned long
> *value, char *type,
> if (it++ != symnum)
> continue;
>
> - strncpy(sym, ksym->name, KSYM_NAME_LEN);
> + strscpy(sym, ksym->name, KSYM_NAME_LEN);
>
> *value = ksym->start;
> *type = BPF_SYM_ELF_TYPE;
> diff --git a/kernel/bpf/log.c b/kernel/bpf/log.c
> index 2a243cf37c60..4bd8f17a9f24 100644
> --- a/kernel/bpf/log.c
> +++ b/kernel/bpf/log.c
> @@ -467,9 +467,9 @@ const char *reg_type_str(struct bpf_verifier_env *env,
> enum bpf_reg_type type)
>
> if (type & PTR_MAYBE_NULL) {
> if (base_type(type) == PTR_TO_BTF_ID)
> - strncpy(postfix, "or_null_", 16);
> + strscpy(postfix, "or_null_");
> else
> - strncpy(postfix, "_or_null", 16);
> + strscpy(postfix, "_or_null");
> }
>
> snprintf(prefix, sizeof(prefix), "%s%s%s%s%s%s%s",
>
> ---
> base-commit: 026e680b0a08a62b1d948e5a8ca78700bfac0e6e
> change-id: 20240402-strncpy-kernel-bpf-core-c-4d8297f95e18
>
> Best regards,
> --
> Justin Stitt <[email protected]>
>
