Messages in this thread | | | Date | Fri, 8 May 2009 11:20:39 +0200 | From | Ingo Molnar <> | Subject | Re: [RFC 1/1] seccomp: Add bitmask of allowed system calls. |
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* Frederic Weisbecker <fweisbec@gmail.com> 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
tracing/filters may lag behind - i'd suggest to use the master branch, that's the most stable stuff generally. Or tracing/core for any Git based tree.
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