linux-kernel - Re: [PATCH] exec: clarify reasoning for euid/egid reset

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Message-ID: <20160412165452.GC19101@ubuntumail>
Date:	Tue, 12 Apr 2016 16:54:52 +0000
From:	Serge Hallyn <serge.hallyn@...ntu.com>
To:	Kees Cook <keescook@...omium.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	David Howells <dhowells@...hat.com>, Willy Tarreau <w@....eu>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] exec: clarify reasoning for euid/egid reset

Quoting Kees Cook (keescook@...omium.org):
> This section of code initially looks redundant, but is required. This
> improves the comment to explain more clearly why the reset is needed.
> 
> Signed-off-by: Kees Cook <keescook@...omium.org>

Thanks, Kees.

Acked-by: Serge E. Hallyn <serge.hallyn@...ntu.com>

> ---
>  fs/exec.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/exec.c b/fs/exec.c
> index c4010b8207a1..889221bbfdb3 100644
> --- a/fs/exec.c
> +++ b/fs/exec.c
> @@ -1387,7 +1387,12 @@ static void bprm_fill_uid(struct linux_binprm *bprm)
>  	kuid_t uid;
>  	kgid_t gid;
>  
> -	/* clear any previous set[ug]id data from a previous binary */
> +	/*
> +	 * Since this can be called multiple times (via prepare_binprm),
> +	 * we must clear any previous work done when setting set[ug]id
> +	 * bits from any earlier bprm->file uses (for example when run
> +	 * first for a script then for its interpreter).
> +	 */
>  	bprm->cred->euid = current_euid();
>  	bprm->cred->egid = current_egid();
>  
> -- 
> 2.6.3
> 
> 
> -- 
> Kees Cook
> Chrome OS & Brillo Security