On Wed, Oct 2, 2013 at 11:48 AM, Djalal Harouni <tixxdz@xxxxxxxxxx> wrote: > On Wed, Oct 02, 2013 at 11:35:45AM -0700, Kees Cook wrote: >> On Wed, Oct 2, 2013 at 11:22 AM, Djalal Harouni <tixxdz@xxxxxxxxxx> wrote: >> > 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 >> >> I didn't mean maps should be 0400. The maps file is already handled >> differently (pinning mm at open time). I didn't think it was one of >> the problematic files. > Kees currently all these files can be used to leak data, except for > /proc/*/{mem,environ} > > These are the only one that pin the mm at open time. But I'm not sure > that this solution will work for /proc/*/maps since they need vma info > which will be perhaps freed if task execv, Need to check it. Ah, yes, you're totally right. I had misremembered. -Kees -- Kees Cook Chrome OS Security -- 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
