On Thu, 2014-06-12 at 20:36 +0100, Ben Hutchings wrote:
> Control: tag -1 security upstream patch moreinfo
> Control: severity -1 grave
> Control: found -1 3.14.5-1
Aurelien Jarno pointed out this appears to be fixed upstream in 3.15:
commit 137f7df8cead00688524c82360930845396b8a21
Author: Markos Chandras <markos.chandras@imgtec.com>
Date: Wed Jan 22 14:40:00 2014 +0000
MIPS: asm: thread_info: Add _TIF_SECCOMP flag
It looks like this can be cherry-picked cleanly onto stable branches for
3.13 and 3.14. For 3.11 and 3.12, it will need trivial adjustment.
For branches older than 3.11, this needs to be cherry-picked first:
commit e7f3b48af7be9f8007a224663a5b91340626fed5
Author: Ralf Baechle <ralf@linux-mips.org>
Date: Wed May 29 01:02:18 2013 +0200
MIPS: Cleanup flags in syscall flags handlers.
Ben.
> On Thu, 2014-06-12 at 16:19 +0000, Plamen Alexandrov wrote:
> > Package: src:linux
> > Version: 3.2.51-1
> > Severity: normal
> >
> > Under MIPS the system call prctl(PR_SET_SECCOMP, 1, ...) does not behave as expected.
> > According to the manual page, after calling it with 1 as a second argument, any consecutive system calls other than read(), write(), _exit() and sigreturn() should result in the delivery of SIGKILL. However, under MIPS any consecutive system call behaves as if prctl(PR_SET_SECCOMP, 1, ...) was never called.
> >
> > Here is a simple example that can be used to reproduce the bug:
> >
> > plamen@debian-mips:/tmp$ id
> > uid=1000(plamen) gid=1000(user) groups=1000(user)
> > plamen@debian-mips:/tmp$ cat prctl.c
> > #include <unistd.h>
> > #include <sys/prctl.h>
> > #include <stdio.h>
> >
> > int main(void)
> > {
> > if (prctl(PR_SET_SECCOMP, 1, 0, 0, 0) != 0)
> > return 0;
> > uid_t uid = getuid();
> > printf("%u\n", (unsigned)uid);
> > return 0;
> > }
> > plamen@debian-mips:/tmp$ gcc prctl.c -o prctl
> > plamen@debian-mips:/tmp$ ./prctl
> > 1000
> >
> > There is no change if I replace
> > if (prctl(PR_SET_SECCOMP, 1, 0, 0, 0) != 0)
> > with
> > if (prctl(PR_SET_SECCOMP, SECCOMP_MODE_STRICT, 0, 0, 0) != 0)
> > and I add #include <linux/seccomp.h>
>
> Indeed, I see no check for seccomp on the MIPS syscall 'fast path'. The
> seccomp check appears to be done on the 'slow path' which is used only
> if tracing or audit is also enabled for the task. If I run the above
> program under strace, it is killed as expected.
>
> Could you test whether the attached patches fix this? (Instructions for
> rebuilding the Debian kernel package with patches can be found at
> <http://kernel-handbook.alioth.debian.org/ch-common-tasks.html#s-common-official>. These patches apply to 'wheezy'.)
>
> Ben.
>
--
Ben Hutchings
The program is absolutely right; therefore, the computer must be wrong.
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