This is a note to let you know that I've just added the patch titled
Sanitize 'move_pages()' permission checks
to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
sanitize-move_pages-permission-checks.patch
and it can be found in the queue-4.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 197e7e521384a23b9e585178f3f11c9fa08274b9 Mon Sep 17 00:00:00 2001
From: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Date: Sun, 20 Aug 2017 13:26:27 -0700
Subject: Sanitize 'move_pages()' permission checks
From: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
commit 197e7e521384a23b9e585178f3f11c9fa08274b9 upstream.
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@xxxxxx>
Acked-by: Eric W. Biederman <ebiederm@xxxxxxxxxxxx>
Cc: Willy Tarreau <w@xxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
mm/migrate.c | 13 ++++---------
1 file changed, 4 insertions(+), 9 deletions(-)
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -38,6 +38,7 @@
#include <linux/balloon_compaction.h>
#include <linux/mmu_notifier.h>
#include <linux/page_idle.h>
+#include <linux/ptrace.h>
#include <asm/tlbflush.h>
@@ -1483,7 +1484,6 @@ SYSCALL_DEFINE6(move_pages, pid_t, pid,
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;
@@ -1507,14 +1507,9 @@ SYSCALL_DEFINE6(move_pages, pid_t, pid,
/*
* 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.
- */
- 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)) {
+ * process. Use the regular "ptrace_may_access()" checks.
+ */
+ if (!ptrace_may_access(task, PTRACE_MODE_READ_REALCREDS)) {
rcu_read_unlock();
err = -EPERM;
goto out;
Patches currently in stable-queue which might be from torvalds@xxxxxxxxxxxxxxxxxxxx are
queue-4.4/x86-asm-64-clear-ac-on-nmi-entries.patch
queue-4.4/sanitize-move_pages-permission-checks.patch
queue-4.4/mm-mempolicy-fix-use-after-free-when-calling-get_mempolicy.patch
queue-4.4/mm-revert-x86_64-and-arm64-elf_et_dyn_base-base-changes.patch