Re: [PATCH v2 0/5] Fix ELF / FDPIC ELF core dumping, and use mmap_sem properly in there

From: ebiederm@xmission.com (Eric W. Biederman)
To: Greg Ungerer <gerg@linux-m68k.org>
Cc: Mark Salter <msalter@redhat.com>, Rich Felker <dalias@libc.org>,
	linux-c6x-dev@linux-c6x.org,
	Yoshinori Sato <ysato@users.sourceforge.jp>,
	Nicolas Pitre <nico@fluxnic.net>,
	Linux-sh list <linux-sh@vger.kernel.org>,
	Jann Horn <jannh@google.com>,
	Russell King - ARM Linux admin <linux@armlinux.org.uk>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Linux-MM <linux-mm@kvack.org>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Oleg Nesterov <oleg@redhat.com>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Aurelien Jacquiot <jacquiot.aurelien@gmail.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Christoph Hellwig <hch@lst.de>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH v2 0/5] Fix ELF / FDPIC ELF core dumping, and use mmap_sem properly in there
Date: Fri, 01 May 2020 11:13:24 +0000	[thread overview]
Message-ID: <87wo5vx60b.fsf@x220.int.ebiederm.org> (raw)
In-Reply-To: <9dd76936-0009-31e4-d869-f64d01886642@linux-m68k.org> (Greg Ungerer's message of "Fri, 1 May 2020 15:44:03 +1000")

Greg Ungerer <gerg@linux-m68k.org> writes:

> On 1/5/20 5:07 am, Eric W. Biederman wrote:
>> Linus Torvalds <torvalds@linux-foundation.org> writes:
>>
>>> On Thu, Apr 30, 2020 at 7:10 AM Greg Ungerer <gerg@linux-m68k.org> wrote:
>>
>>>>> Most of that file goes back to pre-git days. And most of the commits
>>>>> since are not so much about binfmt_flat, as they are about cleanups or
>>>>> changes elsewhere where binfmt_flat was just a victim.
>>>>
>>>> I'll have a look at this.
>>>
>>> Thanks.
>>>
>>>> Quick hack test shows moving setup_new_exec(bprm) to be just before
>>>> install_exec_creds(bprm) works fine for the static binaries case.
>>>> Doing the flush_old_exec(bprm) there too crashed out - I'll need to
>>>> dig into that to see why.
>>>
>>> Just moving setup_new_exec() would at least allow us to then join the
>>> two together, and just say "setup_new_exec() does the credential
>>> installation too".
>>
>> But it is only half a help if we allow failure points between
>> flush_old_exec and install_exec_creds.
>>
>> Greg do things work acceptably if install_exec_creds is moved to right
>> after setup_new_exec? (patch below)
>
> Yes, confirmed. Worked fine with that patch applied.

Good.  Thank you.

That is what we need for other cleanups.  All three of those together.

>> This is what I was thinking about applying.
>>
>> diff --git a/fs/binfmt_flat.c b/fs/binfmt_flat.c
>> index 831a2b25ba79..1a1d1fcb893f 100644
>> --- a/fs/binfmt_flat.c
>> +++ b/fs/binfmt_flat.c
>> @@ -541,6 +541,7 @@ static int load_flat_file(struct linux_binprm *bprm,
>>   		/* OK, This is the point of no return */
>>   		set_personality(PER_LINUX_32BIT);
>>   		setup_new_exec(bprm);
>> +		install_exec_creds(bprm);
>>   	}
>>     	/*
>> @@ -963,8 +964,6 @@ static int load_flat_binary(struct linux_binprm *bprm)
>>   		}
>>   	}
>>   -	install_exec_creds(bprm);
>> -
>>   	set_binfmt(&flat_format);
>>     #ifdef CONFIG_MMU

Eric