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Message-ID: <12824789.NeILaJ7Kvc@machine> Date: Sat, 17 Oct 2020 10:50:00 +0200 From: Francis Laniel <laniel_francis@...vacyrequired.com> To: Kees Cook <keescook@...omium.org> Cc: linux-hardening@...r.kernel.org Subject: Re: [PATCH v1 1/3] Fix unefficient call to memset before memcpu in nla_strlcpy. Le samedi 17 octobre 2020, 01:19:59 CEST Kees Cook a écrit : > On Fri, Oct 16, 2020 at 02:52:14PM +0200, laniel_francis@...vacyrequired.com wrote: > > From: Francis Laniel <laniel_francis@...vacyrequired.com> > > > > This patch solves part 1 of issue: > > https://github.com/KSPP/linux/issues/110 > > > > Signed-off-by: Francis Laniel <laniel_francis@...vacyrequired.com> > > --- > > > > lib/nlattr.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/lib/nlattr.c b/lib/nlattr.c > > index 74019c8ebf6b..ab96a5f4b9b8 100644 > > --- a/lib/nlattr.c > > +++ b/lib/nlattr.c > > @@ -731,8 +731,8 @@ size_t nla_strlcpy(char *dst, const struct nlattr > > *nla, size_t dstsize)> > > if (dstsize > 0) { > > > > size_t len = (srclen >= dstsize) ? dstsize - 1 : srclen; > > > > - memset(dst, 0, dstsize); > > > > memcpy(dst, src, len); > > > > + dst[len] = '\0'; > > I don't think this is right: callers are likely depending on the entire > destination buffer to be zero-padded. I think you probably want: > > memset(dst + len, 0, dstsize - len); > memcpy(dst, src, len); > > (but double-check my pointer math) > I did not understand that the content has to be zero-padded, now your comment on github is clearer! I will modifiy it for next version and check the math on the paper. > > } > > > > return srclen;
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