Re: [PATCH 16/20] tracing/probe: Manual replacement of the deprecated strlcpy() with return values

Romain Perier
2021-02-25T08:39:23Z

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Le lun. 22 févr. 2021 à 18:49, Steven Rostedt <rostedt@goodmis.org> a
écrit :

> > - if (unlikely(!maxlen))
> > - return -ENOMEM;
>
> Don't remove the above. You just broke the else side.
>
> > -
> > - if (addr == FETCH_TOKEN_COMM)
> > - ret = strlcpy(dst, current->comm, maxlen);
> > - else
> > + if (addr == FETCH_TOKEN_COMM) {
> > + ret = strscpy(dst, current->comm, maxlen);
> > + if (ret == -E2BIG)
> > + return -ENOMEM;
>
> I'm not sure the above is what we want. current->comm is always nul
> terminated, and not only that, it will never be bigger than TASK_COMM_LEN.
> If the "dst" location is smaller than comm (maxlen < TASK_COMM_LEN), it is
> still OK to copy a partial string. It should not return -ENOMEM which looks
> to be what happens with this patch.
>
> In other words, it looks like this patch breaks the current code in more
> ways than one.
>
> -- Steve
>

Hello,

Mhhh, *I think* that I had an issue during rebase, I don't remember to have
removed the " if (unlikely(!maxlen))" (sorry for that).
Well, strscpy always returns a truncated string even in case of possible
overflow, the function copies what it can in "dst", it will just return
-E2BIG when
it does not fit or when "count" has a bad value (zero or > INT_MAX). We
have just to make a difference between "-E2BIG, data has been copied to dst
and it is truncated" and "-E2BIG, possible wrong size passed as argument".

I agree that it needs at least to work like before, and I think we can
preserve the old behaviour even with strscpy (we just need to adapt the
error handling accordingly).
I will fix this in v2.

Thanks,
Romain

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