Fix: kernel/ptrace.c: ptrace_peek_siginfo() missing __put_user() validation

This __put_user() could be used by unprivileged processes to write into
kernel memory.  The issue here is that even if copy_siginfo_to_user()
fails, the error code is not checked before __put_user() is executed.

Luckily, ptrace_peek_siginfo() has been added within the 3.10-rc cycle,
so it has not hit a stable release yet.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Acked-by: Oleg Nesterov <oleg@redhat.com>
Cc: Andrey Vagin <avagin@openvz.org>
Cc: Roland McGrath <roland@redhat.com>
Cc: Paul McKenney <paulmck@linux.vnet.ibm.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Dave Jones <davej@redhat.com>
Cc: Pavel Emelyanov <xemul@parallels.com>
Cc: Pedro Alves <palves@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 11 insertions, 9 deletions

diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index aed981a3f69c..335a7ae697f5 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -665,20 +665,22 @@ static int ptrace_peek_siginfo(struct task_struct *child,
                 if (unlikely(is_compat_task())) {
                         compat_siginfo_t __user *uinfo = compat_ptr(data);
 
-                        ret = copy_siginfo_to_user32(uinfo, &info);
-                        ret |= __put_user(info.si_code, &uinfo->si_code);
+                        if (copy_siginfo_to_user32(uinfo, &info) ||
+                            __put_user(info.si_code, &uinfo->si_code)) {
+                                ret = -EFAULT;
+                                break;
+                        }
+
                 } else
 #endif
                 {
                         siginfo_t __user *uinfo = (siginfo_t __user *) data;
 
-                        ret = copy_siginfo_to_user(uinfo, &info);
-                        ret |= __put_user(info.si_code, &uinfo->si_code);
-                }
-
-                if (ret) {
-                        ret = -EFAULT;
-                        break;
+                        if (copy_siginfo_to_user(uinfo, &info) ||
+                            __put_user(info.si_code, &uinfo->si_code)) {
+                                ret = -EFAULT;
+                                break;
+                        }
                 }
 
                 data += sizeof(siginfo_t);