netdev - Re: [PATCH net] tools: ynl: fix string attribute length to include null terminator

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Message-ID: <dqevhqjn5fa2p6v5c4tqjup2hmqndeyemd6bnqssbe2oddaws2@azuqby7offil>
Date: Sat, 25 Oct 2025 21:05:48 +0200
From: Zahari Doychev <zahari.doychev@...ux.com>
To: Petr Oros <poros@...hat.com>
Cc: Jakub Kicinski <kuba@...nel.org>, 
	Donald Hunter <donald.hunter@...il.com>, "David S. Miller" <davem@...emloft.net>, 
	Eric Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>, 
	Jacob Keller <jacob.e.keller@...el.com>, Asbjørn Sloth Tønnesen <ast@...erby.net>, 
	netdev@...r.kernel.org, Ivan Vecera <ivecera@...hat.com>, 
	Michal Schmidt <mschmidt@...hat.com>
Subject: Re: [PATCH net] tools: ynl: fix string attribute length to include
 null terminator

On Sat, Oct 25, 2025 at 08:43:27PM +0200, Petr Oros wrote:
> Yeah, that must be it.
> 
> Regards,
> -Petr

This fixes my problem as well.

thanks

> 
> Dne so 25. 10. 2025 2:03 uživatel Jakub Kicinski <kuba@...nel.org> napsal:
> 
> > On Fri, 24 Oct 2025 15:24:38 +0200 Petr Oros wrote:
> > > The ynl_attr_put_str() function was not including the null terminator
> > > in the attribute length calculation. This caused kernel to reject
> > > CTRL_CMD_GETFAMILY requests with EINVAL:
> > > "Attribute failed policy validation".
> > >
> > > For a 4-character family name like "dpll":
> > > - Sent: nla_len=8 (4 byte header + 4 byte string without null)
> > > - Expected: nla_len=9 (4 byte header + 5 byte string with null)
> > >
> > > The bug was introduced in commit 15d2540e0d62 ("tools: ynl: check for
> > > overflow of constructed messages") when refactoring from stpcpy() to
> > > strlen(). The original code correctly included the null terminator:
> > >
> > >   end = stpcpy(ynl_attr_data(attr), str);
> > >   attr->nla_len = NLA_HDRLEN + NLA_ALIGN(end -
> > >                                 (char *)ynl_attr_data(attr));
> > >
> > > Since stpcpy() returns a pointer past the null terminator, the length
> > > included it. The refactored version using strlen() omitted the +1.
> > >
> > > The fix also removes NLA_ALIGN() from nla_len calculation, since
> > > nla_len should contain actual attribute length, not aligned length.
> > > Alignment is only for calculating next attribute position. This makes
> > > the code consistent with ynl_attr_put().
> > >
> > > CTRL_ATTR_FAMILY_NAME uses NLA_NUL_STRING policy which requires
> > > null terminator. Kernel validates with memchr() and rejects if not
> > > found.
> > >
> > > Fixes: 15d2540e0d62 ("tools: ynl: check for overflow of constructed
> > messages")
> > > Signed-off-by: Petr Oros <poros@...hat.com>
> > > ---
> > >  tools/net/ynl/lib/ynl-priv.h | 4 ++--
> > >  1 file changed, 2 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/tools/net/ynl/lib/ynl-priv.h b/tools/net/ynl/lib/ynl-priv.h
> > > index 29481989ea7662..ced7dce44efb43 100644
> > > --- a/tools/net/ynl/lib/ynl-priv.h
> > > +++ b/tools/net/ynl/lib/ynl-priv.h
> > > @@ -313,7 +313,7 @@ ynl_attr_put_str(struct nlmsghdr *nlh, unsigned int
> > attr_type, const char *str)
> > >       struct nlattr *attr;
> > >       size_t len;
> > >
> > > -     len = strlen(str);
> > > +     len = strlen(str) + 1;
> > >       if (__ynl_attr_put_overflow(nlh, len))
> > >               return;
> > >
> > > @@ -321,7 +321,7 @@ ynl_attr_put_str(struct nlmsghdr *nlh, unsigned int
> > attr_type, const char *str)
> > >       attr->nla_type = attr_type;
> > >
> > >       strcpy((char *)ynl_attr_data(attr), str);
> > > -     attr->nla_len = NLA_HDRLEN + NLA_ALIGN(len);
> > > +     attr->nla_len = NLA_HDRLEN + len;
> > >
> > >       nlh->nlmsg_len += NLMSG_ALIGN(attr->nla_len);
> > >  }
> >
> > looks familiar...
> >
> > Link:
> > https://lore.kernel.org/20251018151737.365485-3-zahari.doychev@linux.com
> >
> >