From: Christoph Hellwig

Sent: 23 July 2020 07:09

The bpfilter user mode helper processes the optval address using
process_vm_readv.  Don't send it kernel addresses fed under
set_fs(KERNEL_DS) as that won't work.

What sort of operations is the bpf filter doing on the sockopt buffers?

Any attempts to reject some requests can be thwarted by a second
application thread modifying the buffer after the bpf filter has
checked that it allowed.

You can't do security by reading a user buffer twice.

	David

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