Suspicious pattern for use of function xt_register_template()

Suspicious pattern for use of function xt_register_template()

[Lukas Bulwahn]

Dear Florian, dear netfilter maintainers,

Commit fdacd57c79b ("netfilter: x_tables: never register tables by
default") on linux-next
introduces the function xt_register_template() and in all cases but
one, the calls to that function are followed by:

    if (ret < 0)
        return ret;

All these checks were also added with the commit above.

In the one case, for iptable_mangle_init() in
./net/ipv4/netfilter/iptable_mangle.c, this pattern was not followed.
This makes this ret assignment in this function a Dead Store and
hence, clang-analyzer warns about that.

Are we missing here an early return for a negative return value as
well, or is this case for iptable_mangle_init() in
./net/ipv4/netfilter/iptable_mangle.c special?


Best regards,

Lukas

Re: Suspicious pattern for use of function xt_register_template()

[Florian Westphal]

Lukas Bulwahn <lukas.bulwahn@gmail.com> wrote:
> Dear Florian, dear netfilter maintainers,
> 
> Commit fdacd57c79b ("netfilter: x_tables: never register tables by
> default") on linux-next
> introduces the function xt_register_template() and in all cases but
> one, the calls to that function are followed by:
> 
>     if (ret < 0)
>         return ret;
> 
> All these checks were also added with the commit above.
> 
> In the one case, for iptable_mangle_init() in
> ./net/ipv4/netfilter/iptable_mangle.c, this pattern was not followed.

Thats a bug, the error test is missing.

Re: Suspicious pattern for use of function xt_register_template()

[Lukas Bulwahn]

On Mon, Aug 23, 2021 at 9:10 PM Florian Westphal <fw@strlen.de> wrote:
>
> Lukas Bulwahn <lukas.bulwahn@gmail.com> wrote:
> > Dear Florian, dear netfilter maintainers,
> >
> > Commit fdacd57c79b ("netfilter: x_tables: never register tables by
> > default") on linux-next
> > introduces the function xt_register_template() and in all cases but
> > one, the calls to that function are followed by:
> >
> >     if (ret < 0)
> >         return ret;
> >
> > All these checks were also added with the commit above.
> >
> > In the one case, for iptable_mangle_init() in
> > ./net/ipv4/netfilter/iptable_mangle.c, this pattern was not followed.
>
> Thats a bug, the error test is missing.

I send out a patch addressing the issue, please pick it:

https://lore.kernel.org/lkml/20210823202729.2009-1-lukas.bulwahn@gmail.com/

Thanks,

Lukas