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[PATCH 3.18 08/10] Sanitize move_pages() permission checks

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3.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Linus Torvalds <torvalds@linux-foundation.org>

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@iki.fi>
Acked-by: Eric W. Biederman <ebiederm@xmission.com>
Cc: Willy Tarreau <w@1wt.eu>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 mm/migrate.c |   13 ++++---------
 1 file changed, 4 insertions(+), 9 deletions(-)

--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -37,6 +37,7 @@
 #include <linux/gfp.h>
 #include <linux/balloon_compaction.h>
 #include <linux/mmu_notifier.h>
+#include <linux/ptrace.h>
 
 #include <asm/tlbflush.h>
 
@@ -1468,7 +1469,6 @@ 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;
@@ -1492,14 +1492,9 @@ 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;

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[PATCH 3.18 00/10] 3.18.67-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-08-22 21:10 +0200
  [PATCH 3.18 05/10] mm/mempolicy: fix use after free when calling get_mempolicy Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-08-22 21:20 +0200
  [PATCH 3.18 02/10] audit: Fix use after free in audit_remove_watch_rule() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-08-22 21:40 +0200
  [PATCH 3.18 01/10] netfilter: nf_ct_ext: fix possible panic after nf_ct_extend_unregister Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-08-22 21:40 +0200
  [PATCH 3.18 09/10] pids: make task_tgid_nr_ns() safe Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-08-22 21:40 +0200
  [PATCH 3.18 06/10] irqchip/atmel-aic: Fix unbalanced of_node_put() in aic_common_irq_fixup() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-08-22 21:40 +0200
  [PATCH 3.18 07/10] irqchip/atmel-aic: Fix unbalanced refcount in aic_common_rtc_irq_fixup() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-08-22 21:40 +0200
  [PATCH 3.18 04/10] ALSA: usb-audio: Apply sample rate quirk to Sennheiser headset Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-08-22 21:40 +0200
  [PATCH 3.18 08/10] Sanitize move_pages() permission checks Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-08-22 21:40 +0200
  [PATCH 3.18 10/10] usb: qmi_wwan: add D-Link DWM-222 device ID Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-08-22 21:40 +0200
  Re: [PATCH 3.18 00/10] 3.18.67-stable review Shuah Khan <shuahkh@osg.samsung.com> - 2017-08-23 02:40 +0200

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