Messages in this thread | | | From | Linus Torvalds <> | Date | Mon, 29 Jun 2020 10:02:48 -0700 | Subject | Re: [PATCH 03/11] fs: add new read_uptr and write_uptr file operations |
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On Mon, Jun 29, 2020 at 8:29 AM Christoph Hellwig <hch@lst.de> wrote: > > So based on that I'd rather get away without our flag and tag the > kernel pointer case in setsockopt explicitly.
Yeah, I'd be ok to pass that kind of flag around for setsockopt, in ways I _don't_ want to do for some very core vfs thing like 'read()'.
That said, is there no practical limit on how big "optlen" can be? Sure, I realize that a lot of setsockopt users may not use all of the data, but let's say that "optlen" is 128, but the actual low-level setsockopt operation only uses the first 16 bytes, maybe we could always just copy the 128 bytes from user space into kernel space, and just say "setsockopt() always gets a kernel pointer".
Then the bpf use is even simpler. It would just pass the kernel pointer natively.
Because that seems to be what the BPF code really wants to do: it takes the user optval, and munges it into a kernel optval, and then (if that has been done) runs the low-level sock_setsockopt() under KERNEL_DS.
Couldn't we switch things around instead, and just *always* copy things from user space, and sock_setsockopt (and sock->ops->setsockopt) _always_ get a kernel buffer?
And avoid the set_fs(KERNEL_DS) games entirely that way?
Attached it a RFC patch just for __sys_setsockopt() - note that it does *not* change all the low-level setsockopt callers to just do the kernel access instead, so this is completely broken, but you can kind of see what I mean.
Wouldn't this work? In fact, wouldn't this simplify all the setsockopt places that now don't need to do "get_user()" etc any more?
It would be better if we could limit "optlen" to something sane, but right now it just does a kmalloc() of whatever the user claims the opt len is..
Linus [unhandled content-type:application/octet-stream] | |