linux-kernel - Re: [PATCH] waitid(): Avoid unbalanced user_access_end() on access

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Message-ID: <67a64016-edb1-98fe-10f9-10cf9ab463a2@caviumnetworks.com>
Date:   Fri, 20 Oct 2017 08:11:40 -0700
From:   David Daney <ddaney@...iumnetworks.com>
To:     Kees Cook <keescook@...omium.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Al Viro <viro@...iv.linux.org.uk>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] waitid(): Avoid unbalanced user_access_end() on
 access_ok() error

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@...iv.linux.org.uk>
> Cc: David Daney <ddaney@...iumnetworks.com>
> Signed-off-by: Kees Cook <keescook@...omium.org>

Thanks Kees,  this looks better to me ...

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

> ---
> 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);
>