[PATCH] bpf: replace deprecated strncpy with strscpy

[PATCH] bpf: replace deprecated strncpy with strscpy

[Justin Stitt]

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>

Re: [PATCH] bpf: replace deprecated strncpy with strscpy

[Ratheesh Kannoth]

On 2024-04-03 at 05:22:50, Justin Stitt (justinstitt@google.com) 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: 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);
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 <justinstitt@google.com>
>

Re: [PATCH] bpf: replace deprecated strncpy with strscpy

[Daniel Borkmann]

On 4/3/24 5:06 AM, Ratheesh Kannoth wrote:
> On 2024-04-03 at 05:22:50, Justin Stitt (justinstitt@google.com) 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: 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);
> You dont have to check return value of strscpy for errors ?

That would be overkill, it can be easily audited that both pointers are
of size KSYM_NAME_LEN, as is the count arg.

Thanks,
Daniel

Re: [PATCH] bpf: replace deprecated strncpy with strscpy

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to bpf/bpf-next.git (master)
by Daniel Borkmann <daniel@iogearbox.net>:

On Tue, 02 Apr 2024 23:52:50 +0000 you 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).
> 
> [...]

Here is the summary with links:
  - bpf: replace deprecated strncpy with strscpy
    https://git.kernel.org/bpf/bpf-next/c/2e114248e086

You are awesome, thank you!
-- 
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