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BACKPORT: Sanitize 'move_pages()' permission checks

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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
Bug: 65468230
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 Artem Borisov
parent 064762f51a
commit 1ceefbf411
1 changed files with 3 additions and 8 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

11
mm/migrate.c
View file

@ -35,6 +35,7 @@
#include <linux/syscalls.h> #include <linux/syscalls.h>
#include <linux/hugetlb.h> #include <linux/hugetlb.h>
#include <linux/gfp.h> #include <linux/gfp.h>
#include <linux/ptrace.h>
#include <asm/tlbflush.h> #include <asm/tlbflush.h>
@ -1372,7 +1373,6 @@ SYSCALL_DEFINE6(move_pages, pid_t, pid, unsigned long, nr_pages,
const int __user *, nodes, const int __user *, nodes,
int __user *, status, int, flags) int __user *, status, int, flags)
{ {
const struct cred *cred = current_cred(), *tcred;
struct task_struct *task; struct task_struct *task;
struct mm_struct *mm; struct mm_struct *mm;
int err; int err;
@ -1396,14 +1396,9 @@ SYSCALL_DEFINE6(move_pages, pid_t, pid, unsigned long, nr_pages,
/* /*
* Check if this process has the right to modify the specified * Check if this process has the right to modify the specified
* process. The right exists if the process has administrative * process. Use the regular "ptrace_may_access()" checks.
* capabilities, superuser privileges or the same
* userid as the target process.
*/ */
tcred = __task_cred(task); if (!ptrace_may_access(task, PTRACE_MODE_READ)) {
if (cred->euid != tcred->suid && cred->euid != tcred->uid &&
cred->uid != tcred->suid && cred->uid != tcred->uid &&
!capable(CAP_SYS_NICE)) {
rcu_read_unlock(); rcu_read_unlock();
err = -EPERM; err = -EPERM;
goto out; goto out;