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From: Al Viro <viro@zeniv.linux.org.uk>
To: Oleg Nesterov <oleg@redhat.com>
Cc: Jann Horn <jannh@google.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Christoph Hellwig <hch@lst.de>,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	linux-fsdevel@vger.kernel.org,
	"Eric W . Biederman" <ebiederm@xmission.com>
Subject: Re: [PATCH v3 2/5] coredump: Let dump_emit() bail out on short writes
Date: Tue, 18 Aug 2020 16:17:07 +0100	[thread overview]
Message-ID: <20200818151707.GD1236603@ZenIV.linux.org.uk> (raw)
In-Reply-To: <20200818134027.GF29865@redhat.com>

On Tue, Aug 18, 2020 at 03:40:28PM +0200, Oleg Nesterov wrote:
> On 08/18, Jann Horn wrote:
> >
> > +	if (dump_interrupted())
> > +		return 0;
> > +	n = __kernel_write(file, addr, nr, &pos);
> > +	if (n != nr)
> > +		return 0;
> > +	file->f_pos = pos;
> 
> Just curious, can't we simply do
> 
> 	__kernel_write(file, addr, nr, &file->f_pos);
> 
> and avoid "loff_t pos" ?

	Bloody bad pattern; it would be (probably) safe in this case,
but in general ->f_pos is shared data.  Exposing it to fuckloads of
->write() instances is a bad idea - we had bugs like that.

	General rule: never pass an address of ->f_pos to anything,
and limit access to it as much as possible.

  parent reply	other threads:[~2020-08-18 15:18 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-08-18  6:12 [PATCH v3 0/5] Fix ELF / FDPIC ELF core dumping, and use mmap_lock properly in there Jann Horn
2020-08-18  6:12 ` Jann Horn
2020-08-18  6:12 ` [PATCH v3 1/5] binfmt_elf_fdpic: Stop using dump_emit() on user pointers on !MMU Jann Horn
2020-08-18  6:12   ` Jann Horn
2020-08-18  6:12 ` [PATCH v3 2/5] coredump: Let dump_emit() bail out on short writes Jann Horn
2020-08-18  6:12   ` Jann Horn
2020-08-18 13:40   ` Oleg Nesterov
2020-08-18 15:08     ` Jann Horn
2020-08-18 15:08       ` Jann Horn
2020-08-18 15:17     ` Al Viro [this message]
2020-08-18  6:12 ` [PATCH v3 3/5] coredump: Refactor page range dumping into common helper Jann Horn
2020-08-18  6:12   ` Jann Horn
2020-08-18  6:12 ` [PATCH v3 4/5] binfmt_elf, binfmt_elf_fdpic: Use a VMA list snapshot Jann Horn
2020-08-18  6:12   ` Jann Horn
2020-08-18  8:18   ` Linus Torvalds
2020-08-18  8:18     ` Linus Torvalds
2020-08-18  8:31     ` Jann Horn
2020-08-18  8:31       ` Jann Horn
2020-08-18  6:12 ` [PATCH v3 5/5] mm/gup: Take mmap_lock in get_dump_page() Jann Horn
2020-08-18  6:12   ` Jann Horn

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