Re: [PATCH 3.10-rc7] Fix: kernel/ptrace.c: ptrace_peek_siginfo() missing __put_user() validation

[Oleg Nesterov <oleg@redhat.com>]

On 06/28, Mathieu Desnoyers wrote:
>
> 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.

Agreed, this looks like 3.10 material.

Acked-by: Oleg Nesterov <oleg@redhat.com>

> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
> CC: Andrey Vagin <avagin@openvz.org>
> CC: Roland McGrath <roland@redhat.com>
> CC: Oleg Nesterov <oleg@redhat.com>
> CC: "Paul E. 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: Linus Torvalds <torvalds@linux-foundation.org>
> Cc: Pedro Alves <palves@redhat.com>
> CC: Andrew Morton <akpm@linux-foundation.org>
> CC: Linus Torvalds <torvalds@linux-foundation.org>
> ---
>  kernel/ptrace.c |   20 +++++++++++---------
>  1 file changed, 11 insertions(+), 9 deletions(-)
> 
> Index: linux/kernel/ptrace.c
> ===================================================================
> --- linux.orig/kernel/ptrace.c
> +++ linux/kernel/ptrace.c
> @@ -665,20 +665,22 @@ static int ptrace_peek_siginfo(struct ta
>  		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);
> 
> -- 
> Mathieu Desnoyers
> EfficiOS Inc.
> http://www.efficios.com