diff options
authorLinus Torvalds <>2017-08-20 13:26:27 -0700
committerLinus Torvalds <>2017-08-20 13:26:27 -0700
commit197e7e521384a23b9e585178f3f11c9fa08274b9 (patch)
parent7f680d7ec3153dffc4d37aea517ead2b9fb9b8e9 (diff)
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 <> Acked-by: Eric W. Biederman <> Cc: Willy Tarreau <> Cc: Signed-off-by: Linus Torvalds <>
1 files changed, 3 insertions, 8 deletions
diff --git a/mm/migrate.c b/mm/migrate.c
index d68a41da6abb..e84eeb4e4356 100644
--- 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>
@@ -1652,7 +1653,6 @@ 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;
@@ -1676,14 +1676,9 @@ 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_REALCREDS)) {
err = -EPERM;
goto out;