queue-4.4/signal-ptrace-don-t-leak-unitialized-kernel-memory-with-ptrace_peek_siginfo.patch

   1 From f6e2aa91a46d2bc79fce9b93a988dbe7655c90c0 Mon Sep 17 00:00:00 2001
   2 From: "Eric W. Biederman" <ebiederm@xmission.com>
   3 Date: Tue, 28 May 2019 18:46:37 -0500
   4 Subject: signal/ptrace: Don't leak unitialized kernel memory with PTRACE_PEEK_SIGINFO
   5
   6 From: Eric W. Biederman <ebiederm@xmission.com>
   7
   8 commit f6e2aa91a46d2bc79fce9b93a988dbe7655c90c0 upstream.
   9
  10 Recently syzbot in conjunction with KMSAN reported that
  11 ptrace_peek_siginfo can copy an uninitialized siginfo to userspace.
  12 Inspecting ptrace_peek_siginfo confirms this.
  13
  14 The problem is that off when initialized from args.off can be
  15 initialized to a negaive value.  At which point the "if (off >= 0)"
  16 test to see if off became negative fails because off started off
  17 negative.
  18
  19 Prevent the core problem by adding a variable found that is only true
  20 if a siginfo is found and copied to a temporary in preparation for
  21 being copied to userspace.
  22
  23 Prevent args.off from being truncated when being assigned to off by
  24 testing that off is <= the maximum possible value of off.  Convert off
  25 to an unsigned long so that we should not have to truncate args.off,
  26 we have well defined overflow behavior so if we add another check we
  27 won't risk fighting undefined compiler behavior, and so that we have a
  28 type whose maximum value is easy to test for.
  29
  30 Cc: Andrei Vagin <avagin@gmail.com>
  31 Cc: stable@vger.kernel.org
  32 Reported-by: syzbot+0d602a1b0d8c95bdf299@syzkaller.appspotmail.com
  33 Fixes: 84c751bd4aeb ("ptrace: add ability to retrieve signals without removing from a queue (v4)")
  34 Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
  35 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  36
  37 ---
  38  kernel/ptrace.c |    9 +++++++--
  39  1 file changed, 7 insertions(+), 2 deletions(-)
  40
  41 --- a/kernel/ptrace.c
  42 +++ b/kernel/ptrace.c
  43 @@ -673,6 +673,10 @@ static int ptrace_peek_siginfo(struct ta
  44         if (arg.nr < 0)
  45                 return -EINVAL;
  46
  47 +       /* Ensure arg.off fits in an unsigned long */
  48 +       if (arg.off > ULONG_MAX)
  49 +               return 0;
  50 +
  51         if (arg.flags & PTRACE_PEEKSIGINFO_SHARED)
  52                 pending = &child->signal->shared_pending;
  53         else
  54 @@ -680,7 +684,8 @@ static int ptrace_peek_siginfo(struct ta
  55
  56         for (i = 0; i < arg.nr; ) {
  57                 siginfo_t info;
  58 -               s32 off = arg.off + i;
  59 +               unsigned long off = arg.off + i;
  60 +               bool found = false;
  61
  62                 spin_lock_irq(&child->sighand->siglock);
  63                 list_for_each_entry(q, &pending->list, list) {
  64 @@ -691,7 +696,7 @@ static int ptrace_peek_siginfo(struct ta
  65                 }
  66                 spin_unlock_irq(&child->sighand->siglock);
  67
  68 -               if (off >= 0) /* beyond the end of the list */
  69 +               if (!found) /* beyond the end of the list */
  70                         break;
  71
  72  #ifdef CONFIG_COMPAT