Re: [PATCH] net: revert "align SO_RCVMARK required privileges with SO_MARK"

[Simon Horman <simon.horman@corigine.com>]

On Mon, Jun 05, 2023 at 05:27:32PM +0200, Larysa Zaremba wrote:
> On Mon, Jun 05, 2023 at 01:12:18AM -0700, Maciej Żenczykowski wrote:
> > This reverts:
> >     commit 1f86123b97491cc2b5071d7f9933f0e91890c976
> >     net: align SO_RCVMARK required privileges with SO_MARK
> > 
> >     The commit referenced in the "Fixes" tag added the SO_RCVMARK socket
> >     option for receiving the skb mark in the ancillary data.
> > 
> >     Since this is a new capability, and exposes admin configured details
> >     regarding the underlying network setup to sockets, let's align the
> >     needed capabilities with those of SO_MARK.
> > 
> 
> No need to copy-paste reverted commit in full. Others are supposed to look it up 
> in the log. The proper way to reference another commit is [0]:
> 
> Commit e21d2170f36602ae2708 ("video: remove unnecessary
> platform_set_drvdata()") removed the unnecessary
> platform_set_drvdata(), but left the variable "dev" unused,
> delete it.
> 
> Have you checked your patch with checkpatch? I am quite sure it would not allow 
> copy-pasted commit message.
> 
> [0] kernel.org/doc/html/v4.17/process/submitting-patches.html
> 
> Also, please add patch prefix with tree name specified (net/net-next).

To add some colour to that, assuming 'net', and with a slightly
fixed-up subject:

	[PATCH net]: Revert "net: align SO_RCVMARK required privileges with SO_MARK"

> 
> > This reasoning is not really correct:
> >   SO_RCVMARK is used for 'reading' incoming skb mark (via cmsg), as such
> >   it is more equivalent to 'getsockopt(SO_MARK)' which has no priv check
> >   and retrieves the socket mark, rather than 'setsockopt(SO_MARK) which
> >   sets the socket mark and does require privs.
> > 
> >   Additionally incoming skb->mark may already be visible if
> >   sysctl_fwmark_reflect and/or sysctl_tcp_fwmark_accept are enabled.
> > 
> >   Furthermore, it is easier to block the getsockopt via bpf
> >   (either cgroup setsockopt hook, or via syscall filters)
> >   then to unblock it if it requires CAP_NET_RAW/ADMIN.
> > 
> > On Android the socket mark is (among other things) used to store
> > the network identifier a socket is bound to.  Setting it is privileged,
> > but retrieving it is not.  We'd like unprivileged userspace to be able
> > to read the network id of incoming packets (where mark is set via iptables
> > [to be moved to bpf])...
> > 
> > An alternative would be to add another sysctl to control whether
> > setting SO_RCVMARK is privilged or not.
> > (or even a MASK of which bits in the mark can be exposed)
> > But this seems like over-engineering...
> > 
> > Note: This is a non-trivial revert, due to later merged:
> >   commit e42c7beee71d0d84a6193357e3525d0cf2a3e168
> >   bpf: net: Consider has_current_bpf_ctx() when testing capable() in sk_setsockopt()
> > which changed both 'ns_capable' into 'sockopt_ns_capable' calls.
> > 
> > Fixes: 1f86123b9749 ("align SO_RCVMARK required privileges with SO_MARK")
> 
> I have never seen a reverted commit referenced with a "Fixes: " tag.

Yes, maybe. Though an example seems to be:

	e7480a44d7c4 ("Revert "net: Remove low_thresh in ip defrag"")

If we do want a fixes tag, then I think it should be:

Fixes: 1f86123b9749 ("net: align SO_RCVMARK required privileges with SO_MARK")

> > Cc: Eyal Birger <eyal.birger@gmail.com>
> > Cc: Jakub Kicinski <kuba@kernel.org>
> > Cc: Eric Dumazet <edumazet@google.com>
> > Cc: Patrick Rohr <prohr@google.com>
> > Signed-off-by: Maciej Żenczykowski <maze@google.com>
> > ---
> >  net/core/sock.c | 6 ------
> >  1 file changed, 6 deletions(-)
> > 
> > diff --git a/net/core/sock.c b/net/core/sock.c
> > index 24f2761bdb1d..6e5662ca00fe 100644
> > --- a/net/core/sock.c
> > +++ b/net/core/sock.c
> > @@ -1362,12 +1362,6 @@ int sk_setsockopt(struct sock *sk, int level, int optname,
> >  		__sock_set_mark(sk, val);
> >  		break;
> >  	case SO_RCVMARK:
> > -		if (!sockopt_ns_capable(sock_net(sk)->user_ns, CAP_NET_RAW) &&
> > -		    !sockopt_ns_capable(sock_net(sk)->user_ns, CAP_NET_ADMIN)) {
> > -			ret = -EPERM;
> > -			break;
> > -		}
> > -
> >  		sock_valbool_flag(sk, SOCK_RCVMARK, valbool);
> >  		break;
> >  
> 
> Both code and your reasoning seem fine.

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