linux-kernel - Re: [PATCH] proc: pid/status: show all supplementary groups

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Message-ID: <20121109152854.GA6778@sergelap>
Date:	Fri, 9 Nov 2012 09:28:54 -0600
From:	Serge Hallyn <serge.hallyn@...onical.com>
To:	Artem Bityutskiy <dedekind1@...il.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Kees Cook <keescook@...omium.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] proc: pid/status: show all supplementary groups

Quoting Artem Bityutskiy (dedekind1@...il.com):
> From: Artem Bityutskiy <artem.bityutskiy@...ux.intel.com>
> 
> We display a list of supplementary group for each process in the
> /proc/<pid>/status. However, we show only the first 32 groups, not all of them.
> 
> Although this is rare, but sometimes processes do have more than 32
> supplementary groups, and this kernel limitation breaks user-space apps
> that rely on the group list in /proc/<pid>/status.
> 
> Number 32 comes from the internal NGROUPS_SMALL macro which defines the
> length for the internal kernel "small" groups buffer. There is no apparent
> reason to limit to this value.
> 
> This patch removes the 32 groups printing limit.
> 
> The Linux kernel limits the amount of supplementary groups by NGROUPS_MAX,
> which is currently set to 65536. And this is the maximum count of groups we
> may possibly print.
> 
> Signed-off-by: Artem Bityutskiy <artem.bityutskiy@...ux.intel.com>

The 'min' is older than git history, but at that dawn of time the code
was just sprintf()ing into a large buffer.

I don't *really* see a problem with this, though if someone did have 1000
groups /proc/$$/status would be sort of annoying to read.  So on the one 
hand adding a '...' in /proc/self/status after 32, and adding a /proc/$$/creds
file seems more pleasant, but then you get into the whole adding files to
/proc kerfuffle, so...

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

> Cc: stable@...r.kernel.org
> ---
>  fs/proc/array.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> NOTE: I consider this to be a bug which breaks user-space, so I add -stable.
> 
> diff --git a/fs/proc/array.c b/fs/proc/array.c
> index c1c207c..bd31e02 100644
> --- a/fs/proc/array.c
> +++ b/fs/proc/array.c
> @@ -212,7 +212,7 @@ static inline void task_state(struct seq_file *m, struct pid_namespace *ns,
>  	group_info = cred->group_info;
>  	task_unlock(p);
>  
> -	for (g = 0; g < min(group_info->ngroups, NGROUPS_SMALL); g++)
> +	for (g = 0; g < group_info->ngroups; g++)
>  		seq_printf(m, "%d ",
>  			   from_kgid_munged(user_ns, GROUP_AT(group_info, g)));
>  	put_cred(cred);
> -- 
> 1.7.7.6
> 
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