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@xxxxxxxxxx) 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@xxxxxxxxxxxxxxx
> > Signed-off-by: Justin Stitt <justinstitt@xxxxxxxxxx>
> > ---
> > 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