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Date: Tue, 02 Apr 2024 23:52:50 +0000
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Message-ID: <20240402-strncpy-kernel-bpf-core-c-v1-1-7cb07a426e78@google.com>
Subject: [PATCH] bpf: replace deprecated strncpy with strscpy
From: Justin Stitt <justinstitt@google.com>
To: Alexei Starovoitov <ast@kernel.org>, Daniel Borkmann <daniel@iogearbox.net>, 
	John Fastabend <john.fastabend@gmail.com>, Andrii Nakryiko <andrii@kernel.org>, 
	Martin KaFai Lau <martin.lau@linux.dev>, Eduard Zingerman <eddyz87@gmail.com>, Song Liu <song@kernel.org>, 
	Yonghong Song <yonghong.song@linux.dev>, KP Singh <kpsingh@kernel.org>, 
	Stanislav Fomichev <sdf@google.com>, Hao Luo <haoluo@google.com>, Jiri Olsa <jolsa@kernel.org>, 
	Nathan Chancellor <nathan@kernel.org>, Nick Desaulniers <ndesaulniers@google.com>, 
	Bill Wendling <morbo@google.com>
Cc: bpf@vger.kernel.org, linux-kernel@vger.kernel.org, llvm@lists.linux.dev, 
	linux-hardening@vger.kernel.org, Justin Stitt <justinstitt@google.com>
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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: linux-hardening@vger.kernel.org
Signed-off-by: Justin Stitt <justinstitt@google.com>
---
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);
 
 		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 <justinstitt@google.com>