Re: [PATCH] waitid(): Avoid unbalanced user_access_end() on access_ok() error

[David Daney]

On 10/20/2017 07:36 AM, Kees Cook wrote:
> As pointed out by Linus and David, the earlier waitid() fix resulted in a
> (currently harmless) unbalanced user_access_end() call. This fixes it to
> just directly return EFAULT on access_ok() failure.
>
> Fixes: 96ca579a1ecc ("waitid(): Add missing access_ok() checks")
> Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
> Cc: David Daney <ddaney@xxxxxxxxxxxxxxxxxx>
> Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>

Thanks Kees,  this looks better to me ...

Acked-by: David Daney <david.daney@xxxxxxxxxx>

> ---
> This seems best to get fixed up now (in the same release where it was
> introduced) before it tries to bite us at some later time.
> ---
>   kernel/exit.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/exit.c b/kernel/exit.c
> index cf28528842bc..f6cad39f35df 100644
> --- a/kernel/exit.c
> +++ b/kernel/exit.c
> @@ -1611,7 +1611,7 @@ SYSCALL_DEFINE5(waitid, int, which, pid_t, upid, struct siginfo __user *,
>   		return err;
>   
>   	if (!access_ok(VERIFY_WRITE, infop, sizeof(*infop)))
> -		goto Efault;
> +		return -EFAULT;
>   
>   	user_access_begin();
>   	unsafe_put_user(signo, &infop->si_signo, Efault);
> @@ -1739,7 +1739,7 @@ COMPAT_SYSCALL_DEFINE5(waitid,
>   		return err;
>   
>   	if (!access_ok(VERIFY_WRITE, infop, sizeof(*infop)))
> -		goto Efault;
> +		return -EFAULT;
>   
>   	user_access_begin();
>   	unsafe_put_user(signo, &infop->si_signo, Efault);