Re: [PATCH 19/20] signalfd: Fix handling of ssi_ptr and ssi_int in signalfd_copyinfo

[Amanieu d'Antras]

Sorry, this was an old version of the patch that was accidentally
sent. Please ignore it.

On Wed, Oct 14, 2015 at 9:59 PM, Amanieu d'Antras <amanieu@xxxxxxxxx> wrote:
> There are several issues here:
> 1) The value of ssi_ptr was incorrect for 32-bit processes. It was
>    previously copied directly from si_ptr, which contains garbage
>    on 32-bit processes, especially on big-endian architectures.
>
> 2) A SIGSYS would cause various fields to be filled with incorrect
>    values. SIGSYS fields are not in signalfd_siginfo, and it should
>    avoid filling in unrelated fields.
>
> 3) ssi_ptr and ssi_int should not be filled in for any unrecognized
>    si_code, but only for those generated by sigqueue. The si_ptr
>    and si_int fields in siginfo_t may not be initialized otherwise.
>
> Signed-off-by: Amanieu d'Antras <amanieu@xxxxxxxxx>
> ---
>  fs/signalfd.c | 42 +++++++++++++++++++++++++++++++-----------
>  1 file changed, 31 insertions(+), 11 deletions(-)
>
> diff --git a/fs/signalfd.c b/fs/signalfd.c
> index 270221f..4d59de9 100644
> --- a/fs/signalfd.c
> +++ b/fs/signalfd.c
> @@ -80,22 +80,43 @@ static unsigned int signalfd_poll(struct file *file, poll_table *wait)
>  static int signalfd_copyinfo(struct signalfd_siginfo __user *uinfo,
>                              siginfo_t const *kinfo)
>  {
> -       long err;
> +       long err, ssi_ptr;
>
>         BUILD_BUG_ON(sizeof(struct signalfd_siginfo) != 128);
>
>         /*
> +        * ssi_ptr for a compat task should be sourced from si_int instead
> +        * of si_ptr since that is what copy_siginfo_from_user32 and
> +        * get_compat_sigevent use. 32-bit pointer values are sign-extended
> +        * to 64 bits when written to ssi_ptr, which matches the behavior of
> +        * 32-bit kernels.
> +        */
> +       ssi_ptr = is_compat_task() ? kinfo->si_int : (long) kinfo->si_ptr;
> +
> +       /*
>          * Unused members should be zero ...
>          */
>         err = __clear_user(uinfo, sizeof(*uinfo));
>
>         /*
> -        * If you change siginfo_t structure, please be sure
> -        * this code is fixed accordingly.
> +        * If you change siginfo_t structure, please be sure that
> +        * all these functions are fixed accordingly:
> +        * copy_siginfo_to_user
> +        * copy_siginfo_to_user32
> +        * copy_siginfo_from_user32
> +        * signalfd_copyinfo
> +        * They should never copy any pad contained in the structure
> +        * to avoid security leaks, but must copy the generic
> +        * 3 ints plus the relevant union member.
>          */
>         err |= __put_user(kinfo->si_signo, &uinfo->ssi_signo);
>         err |= __put_user(kinfo->si_errno, &uinfo->ssi_errno);
>         err |= __put_user((short) kinfo->si_code, &uinfo->ssi_code);
> +       if (kinfo->si_code < 0) {
> +               /* Write ssi_int and ssi_ptr for sigqueue()-generated signals */
> +               err |= __put_user(ssi_ptr, &uinfo->ssi_ptr);
> +               err |= __put_user(kinfo->si_int, &uinfo->ssi_int);
> +       }
>         switch (kinfo->si_code & __SI_MASK) {
>         case __SI_KILL:
>                 err |= __put_user(kinfo->si_pid, &uinfo->ssi_pid);
> @@ -104,7 +125,7 @@ static int signalfd_copyinfo(struct signalfd_siginfo __user *uinfo,
>         case __SI_TIMER:
>                  err |= __put_user(kinfo->si_tid, &uinfo->ssi_tid);
>                  err |= __put_user(kinfo->si_overrun, &uinfo->ssi_overrun);
> -                err |= __put_user((long) kinfo->si_ptr, &uinfo->ssi_ptr);
> +                err |= __put_user(ssi_ptr, &uinfo->ssi_ptr);
>                  err |= __put_user(kinfo->si_int, &uinfo->ssi_int);
>                 break;
>         case __SI_POLL:
> @@ -139,21 +160,20 @@ static int signalfd_copyinfo(struct signalfd_siginfo __user *uinfo,
>         case __SI_MESGQ: /* But this is */
>                 err |= __put_user(kinfo->si_pid, &uinfo->ssi_pid);
>                 err |= __put_user(kinfo->si_uid, &uinfo->ssi_uid);
> -               err |= __put_user((long) kinfo->si_ptr, &uinfo->ssi_ptr);
> +               err |= __put_user(ssi_ptr, &uinfo->ssi_ptr);
>                 err |= __put_user(kinfo->si_int, &uinfo->ssi_int);
>                 break;
> +#ifdef __ARCH_SIGSYS
> +       case __SI_SYS: /* SIGSYS fields are not in signalfd_siginfo */
> +               break;
> +#endif
>         default:
> -               /*
> -                * This case catches also the signals queued by sigqueue().
> -                */
>                 err |= __put_user(kinfo->si_pid, &uinfo->ssi_pid);
>                 err |= __put_user(kinfo->si_uid, &uinfo->ssi_uid);
> -               err |= __put_user((long) kinfo->si_ptr, &uinfo->ssi_ptr);
> -               err |= __put_user(kinfo->si_int, &uinfo->ssi_int);
>                 break;
>         }
>
> -       return err ? -EFAULT: sizeof(*uinfo);
> +       return err ? -EFAULT : sizeof(*uinfo);
>  }
>
>  static ssize_t signalfd_dequeue(struct signalfd_ctx *ctx, siginfo_t *info,
> --
> 2.6.1
>
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