On Sun, Oct 30, 2016 at 11:14:04PM -0500, Eric W. Biederman wrote: > Jann Horn <jann@xxxxxxxxx> writes: > > > On Sat, Oct 01, 2016 at 08:16:00PM -0700, Krister Johansen wrote: > >> On Fri, Sep 23, 2016 at 10:40:38PM +0200, Jann Horn wrote: > >> > +===================== > >> > +FILESYSTEM DEBUG APIS > >> > +===================== > >> > + > >> > +The pid / tgid entries in procfs contain various entries that allow debugging > >> > +access to a process. Interesting entries are: > >> > + > >> > + - auxv permits an ASLR bypass > >> > + - cwd can permit bypassing filesystem restrictions in some cases > >> > + - environ can leak secret tokens > >> > + - fd can permit bypassing filesystem restrictions or leak access to things like > >> > + pipes > >> > + - maps permits an ASLR bypass > >> > + - mem grants R+W access to process memory > >> > + - stat permits an ASLR bypass > >> > + > >> > +Of these, all use both a normal filesystem DAC check (where the file owner is > >> > +the process owner for a dumpable process, root for a nondumpable process) and a > >> > +ptrace_may_access() check; however, the DAC check may be modified, and the > >> > +ptrace_may_access() is performed under PTRACE_FSCREDS, meaning that instead of > >> > +the caller's ruid, rgid and permitted capabilities, the fsuid, fsgid and > >> > +effective capabilities are used, causing the case where a daemon drops its euid > >> > +prior to accessing a file for the user to be treated correctly for this check. > >> > >> Thanks for writing this up. > >> > >> Is it worth mentioning some of the less obvious aspects of how user > >> namespaces interact with the filesystem debug APIs? Of particular note: > >> a nondumpable process will always be assigned the global root ids. > >> Checks against capabilities for procfs require that the uid and gid have > >> a mapping in the current namepsace. That's enforced through > >> capable_wrt_inode_uidgid(). > > > > Yeah, makes sense. Added that. Thanks! > > That will actually be changing for 4.10. mm->user_ns allows me to use > the user namespace id 0 if that id is mapped. I'll be excited to sync up with this change once you land it in 4.10. There are a bunch of tools that get confused if you run them in a user namespace but they can't access /proc/[pid]/whatever. -K -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
