linux-kernel - Re: [PATCH] proc: return on proc

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Date:	Mon, 19 Aug 2013 16:33:07 -0400
From:	Marc Dionne <marc.c.dionne@...il.com>
To:	Richard Genoud <richard.genoud@...il.com>
Cc:	Al Viro <viro@...iv.linux.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] proc: return on proc_readdir error

On Mon, Aug 19, 2013 at 12:30 PM, Richard Genoud
<richard.genoud@...il.com> wrote:
>
> commit f0c3b5093addc8bfe9fe3a5b01acb7ec7969eafa
> "[readdir] convert procfs" introduced a bug on the listing of the proc
> file-system.
> The return value of proc_readdir() isn't tested anymore in the
> proc_root_readdir function.
>
> This lead to an "interesting" behaviour when we are using the getdents()
> system call with a buffer too small:
> Instead of failing, it returns the first entries of /proc (enough to
> fill the given buffer), plus the PID directories.
>
> This is not triggered on glibc (as getdents is called with a 32KB
> buffer), but on uclibc, the buffer size is only 1KB, thus some proc
> entries are missing.
> (described more in details here: https://lkml.org/lkml/2013/8/12/288 )
>
> Signed-off-by: Richard Genoud <richard.genoud@...il.com>
> ---
> [added Linus Torvalds and Andrew Morton in CC since Al Viro seems to be
> on holidays and it's starting to getting late in the -rc cycles]
>
>  fs/proc/root.c |    4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/fs/proc/root.c b/fs/proc/root.c
> index 229e366..e0a790d 100644
> --- a/fs/proc/root.c
> +++ b/fs/proc/root.c
> @@ -205,7 +205,9 @@ static struct dentry *proc_root_lookup(struct inode * dir, struct dentry * dentr
>  static int proc_root_readdir(struct file *file, struct dir_context *ctx)
>  {
>         if (ctx->pos < FIRST_PROCESS_ENTRY) {
> -               proc_readdir(file, ctx);
> +               int error = proc_readdir(file, ctx);
> +               if (unlikely(error <= 0))
> +                       return error;
>                 ctx->pos = FIRST_PROCESS_ENTRY;
>         }

By my reading that commit (f0c3b5093add) also made proc_readdir always
return 0, so with this patch the effect I see is that no pid entries
are listed under /proc, breaking ps for instance.  I don't see how
even the previous version of proc_readdir could return a negative
value; looks like 1 and 0 were the only possible return values.

Marc
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