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Diffstat (limited to 'open_issues/dbus.mdwn')
| -rw-r--r-- | open_issues/dbus.mdwn | 112 |
1 files changed, 112 insertions, 0 deletions
diff --git a/open_issues/dbus.mdwn b/open_issues/dbus.mdwn index a41515a1..4473fba0 100644 --- a/open_issues/dbus.mdwn +++ b/open_issues/dbus.mdwn @@ -253,3 +253,115 @@ See [[glibc]], *Missing interfaces, amongst many more*, *`SOCK_CLOEXEC`*. to know how to find this sendmsg.c file? <pinotree> (it's in glibc, but otherwise the remark is valid) <pinotree> s/otherwise/anyway/ + + +# Emails + +# IRC, freenode, #hurd, 2013-10-16 + + <braunr> gnu_srs: how could you fail to understand credentials need to be + checked ? + <gnu_srs> braunr: If data is sent via sendmsg, no problem, right? + <braunr> gnu_srs: that's irrelevant + <gnu_srs> It's just to move the check to the receive side. + <braunr> and that is the whole problem + <braunr> it's not "just" doing it + <braunr> first, do you know what the receive side is ? + <braunr> do you know what it can be ? + <braunr> do you know where the corresponding source code is to be found ? + <gnu_srs> please, describe a scenario where receiving faulty ancillary data + could be a problem instead + <braunr> dbus + <braunr> a user starting privileged stuff although he's not part of a + privileged group of users for example + <braunr> gnome, kde and others use dbus to pass user ids around + <braunr> if you can't rely on these ids being correct, you can compromise + the whole system + <braunr> because dbus runs as root and can give root privileges + <braunr> or maybe not root, i don't remember but a system user probably + <pinotree> "messagebus" + <gnu_srs> k! + <braunr> see http://www.gnu.org/software/hurd/open_issues/dbus.html + <braunr> IRC, freenode, #hurd, 2013-07-17 + <braunr> <teythoon> and the proper fix is to patch pflocal to query the + auth server and add the credentials? + <braunr> <pinotree> possibly + <braunr> <teythoon> that doesn't sound to bad, did you give it a try? + + +# IRC, freenode, #hurd, 2013-10-22 + + <gnu_srs> I think I have a solution on the receive side for SCM_CREDS :) + + <gnu_srs> A question related to SCM_CREDS: dbus use a zero data byte to get + credentials sent. + <gnu_srs> however, kfreebsd does not care which data (and credentials) is + sent, they report the credentials anyway + <gnu_srs> should the hurd implementation do the same as kfreebsd? + <youpi> gnu_srs: I'm not sure to understand: what happens on linux then? + <youpi> does it see zero data byte as being bogus, and refuse to send the + creds? + <gnu_srs> linux is also transparent, it sends the credentials independent + of the data (but data has to be non-null) + <youpi> ok + <youpi> anyway, what the sending application writes does not matter indeed + <youpi> so we can just ignore that + <youpi> and have creds sent anyway + <braunr> i think the interface normally requires at least a byte of data + for ancilliary data + <youpi> possibly, yes + <braunr> To pass file descriptors or credentials over a SOCK_STREAM, + you need to send or + <braunr> receive at least one byte of non-ancillary data in + the same sendmsg(2) or + <braunr> recvmsg(2) call. + <braunr> but that may simply be linux specific + <braunr> gnu_srs: how do you plan on implementing right checking ? + <gnu_srs> Yes, data has to be sent, at least one byte, I was asking about + e.g. sending an integer + <braunr> just send a zero + <braunr> well + <braunr> dbus already does that + <braunr> just don't change anything + <braunr> let applications pass the data they want + <braunr> the socket interface already deals with port rights correctly + <braunr> what you need to do is make sure the rights received match the + credentials + <gnu_srs> The question is to special case on a zero byte, and forbid + anything else, or allow any data. + <braunr> why would you forbid + <braunr> ? + <gnu_srs> linux and kfreebsd does not special case on a received zero byte + <braunr> same question, why would you want to do that ? + <gnu_srs> linux sends credentials data even if no SCM_CREDENTIALS structure + is created, kfreebsd don't + <braunr> i doubt that + <gnu_srs> To be specific:msgh.msg_control = NULL; msgh.msg_controllen = 0; + <braunr> bbl + <gnu_srs> see the test code: + http://lists.debian.org/debian-hurd/2013/08/msg00091.html + <braunr> back + <braunr> why would the hurd include groups when sending a zero byte, but + only uid when not ? + <gnu_srs> ? + <braunr> 1) Sent credentials are correct: + <braunr> no flags: Hurd: OK, only sent ids + <braunr> -z Hurd: OK, sent IDs + groups + <braunr> and how can it send more than one uid and gid ? + <braunr> "sent credentials are not honoured, received ones are created" + <gnu_srs> Sorry, the implementation is changed by now. And I don't special + case on a zero byte. + <braunr> what does this mean ? + <braunr> then why give me that link ? + <gnu_srs> The code still applies for Linux and kFreeBSD. + <gnu_srs> It means that whatever you send, the kernel emits does not read + that data: see + <gnu_srs> socket.h: before struct cmsgcred: the sender's structure is + ignored ... + <braunr> do you mean receiving on a socket can succeed with gaining + credentials, although the sender sent wrong ones ? + <gnu_srs> Looks like it. I don't have a kfreebsd image available right now. + <gnu_srs> linux returns EPERM + <braunr> anyway + <braunr> how do you plan to implement credential checking ? + <gnu_srs> I'll mail patches RSN |