On Wed, Sep 30, 2015 at 02:48:47PM -0700, Andy Lutomirski wrote: > On Wed, Sep 30, 2015 at 2:39 PM, Tycho Andersen > <tycho.andersen@xxxxxxxxxxxxx> wrote: > > On Wed, Sep 30, 2015 at 11:56:25AM -0700, Andy Lutomirski wrote: > >> On Wed, Sep 30, 2015 at 11:55 AM, Tycho Andersen > >> <tycho.andersen@xxxxxxxxxxxxx> wrote: > >> > On Wed, Sep 30, 2015 at 11:47:05AM -0700, Andy Lutomirski wrote: > >> >> On Wed, Sep 30, 2015 at 11:41 AM, Tycho Andersen > >> >> <tycho.andersen@xxxxxxxxxxxxx> wrote: > >> >> > On Wed, Sep 30, 2015 at 11:25:41AM -0700, Andy Lutomirski wrote: > >> >> >> On Wed, Sep 30, 2015 at 11:13 AM, Tycho Andersen > >> >> >> <tycho.andersen@xxxxxxxxxxxxx> wrote: > >> >> >> > This command allows comparing the underling private data of two fds. This > >> >> >> > is useful e.g. to find out if a seccomp filter is inherited, since struct > >> >> >> > seccomp_filter are unique across tasks and are the private_data seccomp > >> >> >> > fds. > >> >> >> > >> >> >> This is very implementation-specific and may have nasty ABI > >> >> >> consequences far outside seccomp. Let's do something specific to > >> >> >> seccomp and/or eBPF. > >> >> > > >> >> > We could change the name to a less generic KCMP_SECCOMP_FD or > >> >> > something, but without some sort of GUID on each struct > >> >> > seccomp_filter, the implementation would be effectively the same as it > >> >> > is today. Is that enough, or do we need a GUID? > >> >> > > >> >> > >> >> I don't care about the GUID. I think we should name it > >> >> KCMP_SECCOMP_FD and make it only work on seccomp fds. > >> > > >> > Ok, I can do that. > >> > > >> >> Alternatively, we could figure out why KCMP_FILE doesn't do the trick > >> >> and consider fixing it. IMO it's really too bad that struct file is > >> >> so heavyweight that we can't really just embed one in all kinds of > >> >> structures. > >> > > >> > The problem is that KCMP_FILE compares the file objects themselves, > >> > instead of the underlying data. If I ask for a seccomp fd for filter 0 > >> > twice, I'll have two different file objects and they won't be equal. I > >> > suppose we could add some special logic inside KCMP_FILE to compare > >> > the underlying data in special cases (seccomp, ebpf, others?), but it > >> > seems cleaner to have a separate command as you described above. > >> > > >> > >> What I meant was that maybe we could get the two requests to actually > >> produce the same struct file. But that could get very messy > >> memory-wise. > > > > I see. The attached patch seems to work with KCMP_FILE and doesn't > > look too bad if you don't mind the circular references. What do you > > think? > > > > Could be reasonable. I'm not that well versed on what fd_release > does. Are we guaranteed that it's called when the last fd goes away > even if the struct file is pinned by the struct seccomp filter but is > otherwise unreferenced? After thinking about the patch a bit more, I think it's not safe. There is a race where the last referenced is closed at the same time someone else asks for the strcut file via ptrace(). I thought the lock would fix this, but it doesn't. I'll see if I can find another way. Tycho -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
