tcp: take care of mixed splice()/sendmsg(MSG_ZEROCOPY) case
syzbot found that mixing sendpage() and sendmsg(MSG_ZEROCOPY) calls over the same TCP socket would again trigger the infamous warning in inet_sock_destruct() WARN_ON(sk_forward_alloc_get(sk)); While Talal took into account a mix of regular copied data and MSG_ZEROCOPY one in the same skb, the sendpage() path has been forgotten. We want the charging to happen for sendpage(), because pages could be coming from a pipe. What is missing is the downgrading of pure zerocopy status to make sure sk_forward_alloc will stay synced. Add tcp_downgrade_zcopy_pure() helper so that we can use it from the two callers. Fixes: 9b65b17d ("net: avoid double accounting for pure zerocopy skbs") Signed-off-by: Eric Dumazet <edumazet@google.com> Reported-by: syzbot <syzkaller@googlegroups.com> Cc: Talal Ahmad <talalahmad@google.com> Cc: Arjun Roy <arjunroy@google.com> Cc: Willem de Bruijn <willemb@google.com> Acked-by: Soheil Hassas Yeganeh <soheil@google.com> Link: https://lore.kernel.org/r/20220203225547.665114-1-eric.dumazet@gmail.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>
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