Re: [PATCH v2 1/1] net: gro: fix misuse of CB in udp socket lookup

[Paolo Abeni <pabeni@redhat.com>]

Hi Richard,

On Thu, 2023-07-20 at 18:26 +0200, Richard Gobert wrote:
> This patch fixes a misuse of IP{6}CB(skb) in GRO, while calling to
> `udp6_lib_lookup2` when handling udp tunnels. `udp6_lib_lookup2` fetch the
> device from CB. The fix changes it to fetch the device from `skb->dev`.
> l3mdev case requires special attention since it has a master and a slave
> device.
> 
> Fixes: a6024562ffd7 ("udp: Add GRO functions to UDP socket")
> Reported-by: Gal Pressman <gal@nvidia.com>
> Signed-off-by: Richard Gobert <richardbgobert@gmail.com>
> ---
>  include/net/udp.h      |  2 ++
>  net/ipv4/udp.c         | 28 ++++++++++++++++++++++++++--
>  net/ipv4/udp_offload.c |  7 +++++--
>  net/ipv6/udp.c         | 29 +++++++++++++++++++++++++++--
>  net/ipv6/udp_offload.c |  7 +++++--
>  5 files changed, 65 insertions(+), 8 deletions(-)
> 
> diff --git a/include/net/udp.h b/include/net/udp.h
> index 4d13424f8f72..48af1479882f 100644
> --- a/include/net/udp.h
> +++ b/include/net/udp.h
> @@ -299,6 +299,7 @@ int udp_lib_getsockopt(struct sock *sk, int level, int optname,
>  int udp_lib_setsockopt(struct sock *sk, int level, int optname,
>  		       sockptr_t optval, unsigned int optlen,
>  		       int (*push_pending_frames)(struct sock *));
> +void udp4_get_iif_sdif(const struct sk_buff *skb, int *iif, int *sdif);
>  struct sock *udp4_lib_lookup(struct net *net, __be32 saddr, __be16 sport,
>  			     __be32 daddr, __be16 dport, int dif);
>  struct sock *__udp4_lib_lookup(struct net *net, __be32 saddr, __be16 sport,
> @@ -310,6 +311,7 @@ struct sock *udp6_lib_lookup(struct net *net,
>  			     const struct in6_addr *saddr, __be16 sport,
>  			     const struct in6_addr *daddr, __be16 dport,
>  			     int dif);
> +void udp6_get_iif_sdif(const struct sk_buff *skb, int *iif, int *sdif);
>  struct sock *__udp6_lib_lookup(struct net *net,
>  			       const struct in6_addr *saddr, __be16 sport,
>  			       const struct in6_addr *daddr, __be16 dport,
> diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
> index 8c3ebd95f5b9..85eb9977db2c 100644
> --- a/net/ipv4/udp.c
> +++ b/net/ipv4/udp.c
> @@ -550,15 +550,39 @@ static inline struct sock *__udp4_lib_lookup_skb(struct sk_buff *skb,
>  				 inet_sdif(skb), udptable, skb);
>  }
>  
> +/* This function is the alternative to 'inet_iif' and 'inet_sdif'
> + * functions in case we can not rely on fields of IPCB.
> + *
> + * The caller must verify skb_valid_dst(skb) is false and skb->dev is initialized.
> + * The caller must hold the RCU read lock.
> + */
> +inline void udp4_get_iif_sdif(const struct sk_buff *skb, int *iif, int *sdif)

I think you misread David Ahern's suggestion on v1. The idea would be
to move this function (and udp6_get_iif_sdif) in an header file, as
'static inline'[1]. Additionally there is nothing specific about UDP
here so I would rename them inet{,6}_gro_iif_sdif and place them in
include/net/gro.h.

Otherwise LGTM.

Thanks,

Paolo

[1] the usage of the "inline" keyword is basically allowed only in
header files