BACKPORT: Sanitize 'move_pages()' permission checks

The 'move_paghes()' system call was introduced long long ago with the
same permission checks as for sending a signal (except using
CAP_SYS_NICE instead of CAP_SYS_KILL for the overriding capability).

That turns out to not be a great choice - while the system call really
only moves physical page allocations around (and you need other
capabilities to do a lot of it), you can check the return value to map
out some the virtual address choices and defeat ASLR of a binary that
still shares your uid.

So change the access checks to the more common 'ptrace_may_access()'
model instead.

This tightens the access checks for the uid, and also effectively
changes the CAP_SYS_NICE check to CAP_SYS_PTRACE, but it's unlikely that
anybody really _uses_ this legacy system call any more (we hav ebetter
NUMA placement models these days), so I expect nobody to notice.

Famous last words.

Reported-by: Otto Ebeling <otto.ebeling@iki.fi>
Acked-by: Eric W. Biederman <ebiederm@xmission.com>
Cc: Willy Tarreau <w@1wt.eu>
Cc: stable@kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

cherry-picked from: 197e7e521384a23b9e585178f3f11c9fa08274b9

This branch does not have the PTRACE_MODE_REALCREDS flag but its
default behavior is the same as PTRACE_MODE_REALCREDS. So use
PTRACE_MODE_READ instead of PTRACE_MODE_READ_REALCREDS.

Change-Id: I75364561d91155c01f78dd62cdd41c5f0f418854
This commit is contained in:
Marissa Wall 2017-10-09 09:37:32 -07:00 committed by LuK1337
parent ff0eab26dc
commit 88344f35ca

View file

@ -38,6 +38,7 @@
#include <linux/gfp.h>
#include <linux/balloon_compaction.h>
#include <trace/events/kmem.h>
#include <linux/ptrace.h>
#include <asm/tlbflush.h>
@ -1396,7 +1397,6 @@ SYSCALL_DEFINE6(move_pages, pid_t, pid, unsigned long, nr_pages,
const int __user *, nodes,
int __user *, status, int, flags)
{
const struct cred *cred = current_cred(), *tcred;
struct task_struct *task;
struct mm_struct *mm;
int err;
@ -1420,14 +1420,9 @@ SYSCALL_DEFINE6(move_pages, pid_t, pid, unsigned long, nr_pages,
/*
* Check if this process has the right to modify the specified
* process. The right exists if the process has administrative
* capabilities, superuser privileges or the same
* userid as the target process.
* process. Use the regular "ptrace_may_access()" checks.
*/
tcred = __task_cred(task);
if (!uid_eq(cred->euid, tcred->suid) && !uid_eq(cred->euid, tcred->uid) &&
!uid_eq(cred->uid, tcred->suid) && !uid_eq(cred->uid, tcred->uid) &&
!capable(CAP_SYS_NICE)) {
if (!ptrace_may_access(task, PTRACE_MODE_READ)) {
rcu_read_unlock();
err = -EPERM;
goto out;