linux-kernel - Re: [PATCH v2] net: Protect INET_ADDR

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Date:   Fri, 8 May 2020 20:50:25 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Stephen Kitt <steve@....org>
Cc:     "David S . Miller" <davem@...emloft.net>,
        Joe Perches <joe@...ches.com>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] net: Protect INET_ADDR_COOKIE on 32-bit
 architectures

On Fri,  8 May 2020 14:04:57 +0200 Stephen Kitt wrote:
> Commit c7228317441f ("net: Use a more standard macro for
> INET_ADDR_COOKIE") added a __deprecated marker to the cookie name on
> 32-bit architectures, with the intent that the compiler would flag
> uses of the name. However since commit 771c035372a0 ("deprecate the
> '__deprecated' attribute warnings entirely and for good"),
> __deprecated doesn't do anything and should be avoided.
> 
> This patch changes INET_ADDR_COOKIE to declare a dummy struct so that
> any subsequent use of the cookie's name will in all likelihood break
> the build. It also removes the __deprecated marker.
> 
> Signed-off-by: Stephen Kitt <steve@....org>
> ---
> Changes since v1:
>   - use a dummy struct rather than a typedef
> 
>  include/net/inet_hashtables.h | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/include/net/inet_hashtables.h b/include/net/inet_hashtables.h
> index ad64ba6a057f..889d9b00c905 100644
> --- a/include/net/inet_hashtables.h
> +++ b/include/net/inet_hashtables.h
> @@ -301,8 +301,9 @@ static inline struct sock *inet_lookup_listener(struct net *net,
>  	  ((__sk)->sk_bound_dev_if == (__sdif)))		&&	\
>  	 net_eq(sock_net(__sk), (__net)))
>  #else /* 32-bit arch */
> +/* Break the build if anything tries to use the cookie's name. */

I think the macro is supposed to cause a warning when the variable
itself is accessed. And I don't think that happens with your patch
applied.

diff --git a/net/ipv4/inet_hashtables.c b/net/ipv4/inet_hashtables.c
index 2bbaaf0c7176..6c4a3904ed8b 100644
--- a/net/ipv4/inet_hashtables.c
+++ b/net/ipv4/inet_hashtables.c
@@ -360,6 +360,8 @@ struct sock *__inet_lookup_established(struct net *net,
        unsigned int slot = hash & hashinfo->ehash_mask;
        struct inet_ehash_bucket *head = &hashinfo->ehash[slot];
 
+       kfree(&acookie);
 begin:
        sk_nulls_for_each_rcu(sk, node, &head->chain) {
                if (sk->sk_hash != hash)

$ make ARCH=i386
make[1]: Entering directory `/netdev/net-next/build_allmodconfig_warn_32bit'
  GEN     Makefile
  CALL    ../scripts/atomic/check-atomics.sh
  CALL    ../scripts/checksyscalls.sh
  CHK     include/generated/compile.h
  CC      net/ipv4/inet_hashtables.o
  CHK     kernel/kheaders_data.tar.xz
  AR      net/ipv4/built-in.a
  AR      net/built-in.a
  GEN     .version
  CHK     include/generated/compile.h
  UPD     include/generated/compile.h
  CC      init/version.o
  AR      init/built-in.a
  LD      vmlinux.o
  MODPOST vmlinux.o

Builds fine.

>  #define INET_ADDR_COOKIE(__name, __saddr, __daddr) \
> -	const int __name __deprecated __attribute__((unused))
> +	struct {} __name __attribute__((unused))
>  
>  #define INET_MATCH(__sk, __net, __cookie, __saddr, __daddr, __ports, __dif, __sdif) \
>  	(((__sk)->sk_portpair == (__ports))		&&		\