Re: [PATCH net-next v3] sctp: add bpf_bypass_getsockopt proto callback

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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@xxxxxxxxxxxxx/
> 
> Fixes: 0d01da6afc54 ("bpf: implement getsockopt and setsockopt hooks")
> Cc: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
> Cc: Christian Brauner <brauner@xxxxxxxxxx>
> Cc: Stanislav Fomichev <sdf@xxxxxxxxxx>
> Cc: Neil Horman <nhorman@xxxxxxxxxxxxx>
> Cc: Marcelo Ricardo Leitner <marcelo.leitner@xxxxxxxxx>
> Cc: Xin Long <lucien.xin@xxxxxxxxx>
> Cc: linux-sctp@xxxxxxxxxxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> Cc: netdev@xxxxxxxxxxxxxxx
> Suggested-by: Stanislav Fomichev <sdf@xxxxxxxxxx>
> Acked-by: Stanislav Fomichev <sdf@xxxxxxxxxx>
> Signed-off-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@xxxxxxxxxxxxx>
> ---

Reviewed-by: Christian Brauner <brauner@xxxxxxxxxx>



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