linux-kernel - Re: [PATCH net-next v3] sctp: add bpf_bypass

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Message-ID: <20230515-unberechenbar-ergoss-4a2fc34870a0@brauner>
Date:   Mon, 15 May 2023 10:16:03 +0200
From:   Christian Brauner <brauner@...nel.org>
To:     Alexander Mikhalitsyn <aleksandr.mikhalitsyn@...onical.com>
Cc:     nhorman@...driver.com, davem@...emloft.net,
        Daniel Borkmann <daniel@...earbox.net>,
        Stanislav Fomichev <sdf@...gle.com>,
        Marcelo Ricardo Leitner <marcelo.leitner@...il.com>,
        Xin Long <lucien.xin@...il.com>, linux-sctp@...r.kernel.org,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH net-next v3] sctp: add bpf_bypass_getsockopt proto
 callback

On Thu, May 11, 2023 at 03:25:06PM +0200, Alexander Mikhalitsyn wrote:
> Implement ->bpf_bypass_getsockopt proto callback and filter out
> SCTP_SOCKOPT_PEELOFF, SCTP_SOCKOPT_PEELOFF_FLAGS and SCTP_SOCKOPT_CONNECTX3
> socket options from running eBPF hook on them.
> 
> SCTP_SOCKOPT_PEELOFF and SCTP_SOCKOPT_PEELOFF_FLAGS options do fd_install(),
> and if BPF_CGROUP_RUN_PROG_GETSOCKOPT hook returns an error after success of
> the original handler sctp_getsockopt(...), userspace will receive an error
> from getsockopt syscall and will be not aware that fd was successfully
> installed into a fdtable.
> 
> As pointed by Marcelo Ricardo Leitner it seems reasonable to skip
> bpf getsockopt hook for SCTP_SOCKOPT_CONNECTX3 sockopt too.
> Because internaly, it triggers connect() and if error is masked
> then userspace will be confused.
> 
> This patch was born as a result of discussion around a new SCM_PIDFD interface:
> https://lore.kernel.org/all/20230413133355.350571-3-aleksandr.mikhalitsyn@canonical.com/
> 
> Fixes: 0d01da6afc54 ("bpf: implement getsockopt and setsockopt hooks")
> Cc: Daniel Borkmann <daniel@...earbox.net>
> Cc: Christian Brauner <brauner@...nel.org>
> Cc: Stanislav Fomichev <sdf@...gle.com>
> Cc: Neil Horman <nhorman@...driver.com>
> Cc: Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
> Cc: Xin Long <lucien.xin@...il.com>
> Cc: linux-sctp@...r.kernel.org
> Cc: linux-kernel@...r.kernel.org
> Cc: netdev@...r.kernel.org
> Suggested-by: Stanislav Fomichev <sdf@...gle.com>
> Acked-by: Stanislav Fomichev <sdf@...gle.com>
> Signed-off-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@...onical.com>
> ---

Reviewed-by: Christian Brauner <brauner@...nel.org>