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Message-ID: <alpine.LFD.2.21.1904020000230.4710@ja.home.ssi.bg> Date: Tue, 2 Apr 2019 00:05:20 +0300 (EEST) From: Julian Anastasov <ja@....bg> To: Eric Dumazet <edumazet@...gle.com> cc: "David S . Miller" <davem@...emloft.net>, netdev <netdev@...r.kernel.org>, Eric Dumazet <eric.dumazet@...il.com> Subject: Re: [PATCH net] tcp: fix tcp_inet6_sk() for 32bit kernels Hello, On Mon, 1 Apr 2019, Eric Dumazet wrote: > It turns out that struct ipv6_pinfo is not located as we think. > > inet6_sk_generic() and tcp_inet6_sk() disagree on 32bit kernels by 4-bytes, > because struct tcp_sock has 8-bytes alignment, > but ipv6_pinfo size is not a multiple of 8. > > sizeof(struct ipv6_pinfo): 116 (not padded to 8) > > I actually first coded tcp_inet6_sk() as this patch does, but thought > that "container_of(tcp_sk(sk), struct tcp6_sock, tcp)" was cleaner. > > As Julian told me : Nobody should use tcp6_sock.inet6 > directly, it should be accessed via tcp_inet6_sk() or inet6_sk(). > > This happened when we added the first u64 field in struct tcp_sock. > > Fixes: 93a77c11ae79 ("tcp: add tcp_inet6_sk() helper") > Signed-off-by: Eric Dumazet <edumazet@...gle.com> > Bisected-by: Julian Anastasov <ja@....bg> > --- > net/ipv6/tcp_ipv6.c | 5 +++-- > 1 file changed, 3 insertions(+), 2 deletions(-) > > diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c > index eec814fe53b817106bc1d1eaa89dadcb96c974fa..82018bdce863165eba72e1ccf0c12ee558042ae8 100644 > --- a/net/ipv6/tcp_ipv6.c > +++ b/net/ipv6/tcp_ipv6.c > @@ -93,12 +93,13 @@ static struct tcp_md5sig_key *tcp_v6_md5_do_lookup(const struct sock *sk, > /* Helper returning the inet6 address from a given tcp socket. > * It can be used in TCP stack instead of inet6_sk(sk). > * This avoids a dereference and allow compiler optimizations. > + * It is a specialized version of inet6_sk_generic(). > */ > static struct ipv6_pinfo *tcp_inet6_sk(const struct sock *sk) > { > - struct tcp6_sock *tcp6 = container_of(tcp_sk(sk), struct tcp6_sock, tcp); > + unsigned int offset = sizeof(struct tcp6_sock) - sizeof(struct ipv6_pinfo); > > - return &tcp6->inet6; > + return (struct ipv6_pinfo *)(((u8 *)sk) + offset); > } > > static void inet6_sk_rx_dst_set(struct sock *sk, const struct sk_buff *skb) Thanks Eric! It is working here. Regards -- Julian Anastasov <ja@....bg>
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