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

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