4.12-stable review patch. If anyone has any objections, please let me know.
------------------
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
@@ -41,6 +41,7 @@
#include <linux/page_idle.h>
#include <linux/page_owner.h>
#include <linux/sched/mm.h>
+#include <linux/ptrace.h>
#include <asm/tlbflush.h>
@@ -1649,7 +1650,6 @@ 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;
@@ -1673,14 +1673,9 @@ 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;