On Wed, Oct 02, 2013 at 10:48:55AM -0700, Kees Cook wrote: > On Wed, Oct 2, 2013 at 9:51 AM, Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote: > > On Wed, Oct 2, 2013 at 3:37 PM, Djalal Harouni <tixxdz@xxxxxxxxxx> wrote: > >> On Tue, Oct 01, 2013 at 06:40:41PM -0700, Andy Lutomirski wrote: > >>> On 10/01/2013 01:26 PM, Djalal Harouni wrote: > >>> > /proc/<pid>/* entries varies at runtime, appropriate permission checks > >>> > need to happen during each system call. > >>> > > >>> > Currently some of these sensitive entries are protected by performing > >>> > the ptrace_may_access() check. However even with that the /proc file > >>> > descriptors can be passed to a more privileged process > >>> > (e.g. a suid-exec) which will pass the classic ptrace_may_access() > >>> > check. In general the ->open() call will be issued by an unprivileged > >>> > process while the ->read(),->write() calls by a more privileged one. > >>> > > >>> > Example of these files are: > >>> > /proc/*/syscall, /proc/*/stack etc. > >>> > > >>> > And any open(/proc/self/*) then suid-exec to read()/write() /proc/self/* > >>> > > >>> > > >>> > These files are protected during read() by the ptrace_may_access(), > >>> > however the file descriptor can be passed to a suid-exec which can be > >>> > used to read data and bypass ASLR. Of course this was discussed several > >>> > times on LKML. > >>> > >>> Can you elaborate on what it is that you're fixing? That is, can you > >>> give a concrete example of what process opens what file and passes the > >>> fd to what process? > >> Yes, the references were already given in this email: > >> https://lkml.org/lkml/2013/8/31/209 > >> > >> This has been discussed several times on lkml: > >> https://lkml.org/lkml/2013/8/28/544 > >> > >> https://lkml.org/lkml/2013/8/28/564 (check Kees's references) > >> > >> > >>> I'm having trouble following your description. > >> Process open a /proc file and pass the fd to a more privilaged process > >> that will pass the ptrace_may_access() check, while the original process > >> that opened that file should fail at the ptrace_may_access() > > > > So we're talking about two kinds of attacks, right? > > Correct. > > > Type 1: Unprivileged process does something like open("/proc/1/maps", > > O_RDONLY) and then passes the resulting fd to something privileged. > > ... and then leaks contents back to unprivileged process. > > > Type 2: Unprivileged process does something like > > open("/proc/self/maps", O_RDONLY) and then forks. The parent calls > > execve on something privileged. > > ... and then parent snoops on file contents for the privileged child. > > (Type 2 is solved currently, IIUC. Type 1 could be reduced in scope by > changing these file modes back to 0400.) Kees for 0400 on /proc/*/maps, it was reported that it could break glibc Even with 0444 this series will catch it, take a look at /proc/*/stat example, we just delay the check that is suposed to be done during ->open() into ->read(), if the cred change of course -- Djalal Harouni http://opendz.org -- 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
