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Date: Fri, 29 Jun 2018 10:13:30 -0700
From: Paul Burton <paul.burton@mips.com>
To: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: "Maciej W. Rozycki" <macro@mips.com>,
        James Hogan <jhogan@kernel.org>,
        Ralf Baechle <ralf@linux-mips.org>,
        linux-fsdevel@vger.kernel.org, linux-mips@linux-mips.org,
        linux-kernel@vger.kernel.org, stable@vger.kernel.org
Subject: Re: [PATCH 1/3] binfmt_elf: Respect error return from
 `regset->active'
Message-ID: <20180629171330.4giikc5x2cbxxuyc@pburton-laptop>
References: <alpine.DEB.2.00.1804301557320.11756@tp.orcam.me.uk>
 <alpine.DEB.2.00.1805102009380.10896@tp.orcam.me.uk>
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Hi Alexander,

On Tue, May 15, 2018 at 11:32:45PM +0100, Maciej W. Rozycki wrote:
> The regset API documented in <linux/regset.h> defines -ENODEV as the 
> result of the `->active' handler to be used where the feature requested 
> is not available on the hardware found.  However code handling core file 
> note generation in `fill_thread_core_info' interpretes any non-zero 
> result from the `->active' handler as the regset requested being active. 
> Consequently processing continues (and hopefully gracefully fails later 
> on) rather than being abandoned right away for the regset requested.
> 
> Fix the problem then by making the code proceed only if a positive 
> result is returned from the `->active' handler.
> 
> Cc: stable@vger.kernel.org # 2.6.25+
> Fixes: 4206d3aa1978 ("elf core dump: notes user_regset")
> Signed-off-by: Maciej W. Rozycki <macro@mips.com>

<snip>

> --- linux-jhogan-test.orig/fs/binfmt_elf.c	2018-03-21 17:14:55.000000000 +0000
> +++ linux-jhogan-test/fs/binfmt_elf.c	2018-05-09 23:25:50.742255000 +0100
> @@ -1739,7 +1739,7 @@ static int fill_thread_core_info(struct 
>  		const struct user_regset *regset = &view->regsets[i];
>  		do_thread_regset_writeback(t->task, regset);
>  		if (regset->core_note_type && regset->get &&
> -		    (!regset->active || regset->active(t->task, regset))) {
> +		    (!regset->active || regset->active(t->task, regset) > 0)) {
>  			int ret;
>  			size_t size = regset_size(t->task, regset);
>  			void *data = kmalloc(size, GFP_KERNEL);
> 

This looks obviously right to me, although I don't think it affects
anything until commit 25847fb195ae ("powerpc/ptrace: Enable support for
NT_PPC_CGPR") in v4.8-rc1 & even then not in a harmful way so I'd drop
the stable tag.

You show up as maintainer for fs/binfmt_elf.c though, so before I go
applying this to mips-next does it look good to you?

Thanks,
    Paul