Re: [PATCH net v4 2/3] net: prevent rewrite of msg_name in sock_sendmsg()

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Jordan Rife wrote:
> Callers of sock_sendmsg(), and similarly kernel_sendmsg(), in kernel
> space may observe their value of msg_name change in cases where BPF
> sendmsg hooks rewrite the send address. This has been confirmed to break
> NFS mounts running in UDP mode and has the potential to break other
> systems.
> This patch:
> 1) Creates a new function called __sock_sendmsg() with same logic as the
>    old sock_sendmsg() function.
> 2) Replaces calls to sock_sendmsg() made by __sys_sendto() and
>    __sys_sendmsg() with __sock_sendmsg() to avoid an unnecessary copy,
>    as these system calls are already protected.
> 3) Modifies sock_sendmsg() so that it makes a copy of msg_name if
>    present before passing it down the stack to insulate callers from
>    changes to the send address.
> Link:
> Fixes: 1cedee13d25a ("bpf: Hooks for sys_sendmsg")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Jordan Rife <jrife@xxxxxxxxxx>

Reviewed-by: Willem de Bruijn <willemb@xxxxxxxxxx>

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