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authorLinus Torvalds <torvalds@linux-foundation.org>2017-08-20 13:26:27 -0700
committerBen Hutchings <ben@decadent.org.uk>2017-09-15 18:30:57 +0100
commita9a659c916c81b3385479ee00d4547912f08abf6 (patch)
parent125a66961a14d740fe1a0a5398c2aaf7f715d17e (diff)
Sanitize 'move_pages()' permission checks
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> [bwh: Backported to 3.2: adjust context] Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
1 files changed, 3 insertions, 8 deletions
diff --git a/mm/migrate.c b/mm/migrate.c
index 0f2736b319de..3f95bab563cb 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -34,6 +34,7 @@
#include <linux/syscalls.h>
#include <linux/hugetlb.h>
#include <linux/gfp.h>
+#include <linux/ptrace.h>
#include <asm/tlbflush.h>
@@ -1366,7 +1367,6 @@ 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;
@@ -1390,14 +1390,9 @@ 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 (cred->euid != tcred->suid && cred->euid != tcred->uid &&
- cred->uid != tcred->suid && cred->uid != tcred->uid &&
- !capable(CAP_SYS_NICE)) {
+ if (!ptrace_may_access(task, PTRACE_MODE_READ_REALCREDS)) {
err = -EPERM;
goto out;