netdev - Re: [PATCH v7 4/8] bpftool: Ensure task comm is always NUL-terminated

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Message-ID: <CALOAHbAzSAQMtts5x+OMDDy1ZY5icUJv2wAM5w74ffhtEbN1mQ@mail.gmail.com>
Date: Sun, 18 Aug 2024 10:27:01 +0800
From: Yafang Shao <laoar.shao@...il.com>
To: Alejandro Colomar <alx@...nel.org>
Cc: akpm@...ux-foundation.org, torvalds@...ux-foundation.org, 
	justinstitt@...gle.com, ebiederm@...ssion.com, alexei.starovoitov@...il.com, 
	rostedt@...dmis.org, catalin.marinas@....com, 
	penguin-kernel@...ove.sakura.ne.jp, linux-mm@...ck.org, 
	linux-fsdevel@...r.kernel.org, linux-trace-kernel@...r.kernel.org, 
	audit@...r.kernel.org, linux-security-module@...r.kernel.org, 
	selinux@...r.kernel.org, bpf@...r.kernel.org, netdev@...r.kernel.org, 
	dri-devel@...ts.freedesktop.org, Quentin Monnet <qmo@...nel.org>
Subject: Re: [PATCH v7 4/8] bpftool: Ensure task comm is always NUL-terminated

On Sat, Aug 17, 2024 at 4:39 PM Alejandro Colomar <alx@...nel.org> wrote:
>
> Hi Yafang,
>
> On Sat, Aug 17, 2024 at 10:56:20AM GMT, Yafang Shao wrote:
> > Let's explicitly ensure the destination string is NUL-terminated. This way,
> > it won't be affected by changes to the source string.
> >
> > Signed-off-by: Yafang Shao <laoar.shao@...il.com>
> > Reviewed-by: Quentin Monnet <qmo@...nel.org>
> > ---
> >  tools/bpf/bpftool/pids.c | 2 ++
> >  1 file changed, 2 insertions(+)
> >
> > diff --git a/tools/bpf/bpftool/pids.c b/tools/bpf/bpftool/pids.c
> > index 9b898571b49e..23f488cf1740 100644
> > --- a/tools/bpf/bpftool/pids.c
> > +++ b/tools/bpf/bpftool/pids.c
> > @@ -54,6 +54,7 @@ static void add_ref(struct hashmap *map, struct pid_iter_entry *e)
> >               ref = &refs->refs[refs->ref_cnt];
> >               ref->pid = e->pid;
> >               memcpy(ref->comm, e->comm, sizeof(ref->comm));
> > +             ref->comm[sizeof(ref->comm) - 1] = '\0';
>
> Why doesn't this use strscpy()?

bpftool is a userspace tool, so strscpy() is only applicable in kernel
code, correct?

> Isn't the source terminated?

It is currently terminated, but I believe we should avoid relying on
the source. Making it independent of the source would reduce potential
errors.

>
> Both the source and the destination measure 16 characters.  If it is
> true that the source is not terminated, then this copy might truncate
> the (non-)string by overwriting the last byte with a NUL.  Is that
> truncation a good thing?

It's not ideal, but we should still convert it to a string, even if it
ends up being truncated.

--
Regards
Yafang