Messages in this thread | | | Date | Fri, 8 May 2009 13:12:23 +0200 | From | Frederic Weisbecker <> | Subject | Re: [RFC 1/1] seccomp: Add bitmask of allowed system calls. |
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On Fri, May 08, 2009 at 12:32:25AM -0500, Tom Zanussi wrote: > On Fri, 2009-05-08 at 01:00 +0200, Frederic Weisbecker wrote: > > On Thu, May 07, 2009 at 03:34:58PM -0700, Adam Langley wrote: > > > > That assessment is incorrect, there's no difference between safety > > > > here really. > > > > > > > > LSM cannot magically inspect user-space memory either when multiple > > > > threads may access it. The point would be to define filters for > > > > system call _arguments_, which are inherently thread-local and safe. > > > > > > If I hook security_operations.socket_connect, I can validate the struct > > > sockaddr after the final copy_from_user. However, since the sockaddr lives in > > > userspace memory, if I try and validate it from ftrace SYSCALL_ENTER, I can't > > > know that it won't change before sys_connect reads it again. > > > > > > Because of that, there are system calls which an LSM hook can safely accept > > > that an ftrace hook cannot. However, as you point out, any arguments passed in > > > registers are inheriently safe and these may be sufficiently powerful. > > > > > > > There are two problems with the bitmap scheme, which i also > > > > suggested in a previous thread but then found it to be lacking: > > > > > > > > 1) enumeration: you define a bitmap. That will be problematic > > > > between compat and native 64-bit (both have different syscall > > > > vectors). > > > > > > I /think/ it works out, but I've been bitten before with subtle 32/64 bit > > > compat issues and accept that it's a bit ugly. > > > > > > > 2) flexibility. It's an on/off selection per syscall. With the > > > > filter we have on, off, or filtered. That's a _whole_ lot more > > > > flexible. > > > > > > Absolutely. > > > > > > Is there a git tree that I can pull this parsing code from? > > > (git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-2.6-trace.git > > > maybe?). I can patch in the seccomp-on-ftrace work and try building the > > > filtering on top of that. I'll see how it turns out anyway. > > > > > > Hi, > > > > The most uptodate one is: > > git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip.git > > on the tracing/filters topic. > > > > See kernel/trace/trace_events_filter.c > > > > You might want to reuse some current syscall tracing facility. > > An automated resolution table is built on bootime, you can look > > at the end of arch/x86/kernel/ftrace.c > > > > This table links each syscalls nr to the matching attribute entry of syscall > > in which you can find: > > > > - parameters names > > - parameters types > > - syscall name > > > > I guess it would be easier for seccomp to make use of the filtering and > reuse the syscall tracing facility if we added filtering to the syscall > tracer first. It would be useful to do for the syscall tracer anyway, > regardless of whether it (or something similar) ended up being used by > seccomp. > > Frederic, did you have any plans for that? If not, I can take a look > when I get the chance... > > Tom
You're totally right! Well, I will not have enough time for that until next week-end. So if you have free slots for that, don't hesitate :)
Thanks!
Frederic.
> > > You can look at the hooks in include/linux/syscall.h: > > The sections inside > > #ifdef CONFIG_FTRACE_SYSCALLS > > > > Well, it's a bit insane to read, so you can also look > > at include/trace/syscall.h and kernel/trace/trace_syscalls.c and > > see how it is used and how it could be reused. > > > > > > Thanks, > > Frederic. > > >
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