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bh=qmfN1/nZWFYxeYB8LHJmYXp/zoyQ9JZ4CGLm4sEKFQs=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=hw3Jox4le087rkMSVEXUWHYw3A5AGUk8FE4Rf5JhrZBD1A33Hc4JEDG7/+pFbio56 tkUykuJxMXDFbbyy5V40rf/CdWLMa/D90ZdQGHSdR4+l4Tph/lvSfF7Ao76rW7TkuK wchTJPzFkwEr021R2I7kxNpHowo/90buDdLNQoFc= Date: Wed, 5 Apr 2023 20:09:23 -0700 From: Andrew Morton To: jaewon31.kim@samsung.com Cc: "jstultz@google.com" , "tjmercier@google.com" , "sumit.semwal@linaro.org" , "daniel.vetter@ffwll.ch" , "hannes@cmpxchg.org" , "mhocko@kernel.org" , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , "jaewon31.kim@gmail.com" Subject: Re: [PATCH v2] dma-buf/heaps: system_heap: Avoid DoS by limiting single allocations to half of all memory Message-Id: <20230405200923.9b0dca2165ef3335a0f6b112@linux-foundation.org> In-Reply-To: <20230406021712epcms1p216f274040d25d18380668ffbfa809c48@epcms1p2> References: <20230405185650.239f9721f066aa480e83d543@linux-foundation.org> <20230405172524.e25b62e1c548a95564b1d324@linux-foundation.org> <20230406000854.25764-1-jaewon31.kim@samsung.com> <20230406014419epcms1p3f285b6e3fdbb1457db1bcbaab9e863be@epcms1p3> <20230406021712epcms1p216f274040d25d18380668ffbfa809c48@epcms1p2> X-Mailer: Sylpheed 3.7.0 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 09B9C100011 X-Rspam-User: X-Stat-Signature: ttwj4qmeboju6az8swpykruw9ct3satm X-HE-Tag: 1680750565-194667 X-HE-Meta: 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 cWGnJhuD X4PoePr3OmkoUmjlBygB2mv8a4hC7Ngz78a6rKm2EtobVo5ACLVCovr5qCRz+/WLK8ALzqdHnm3Tn8ZLvOOmbwKhvCmid54QuWwHWd90yYI81O531dFowtjtN8CDITodr3t1nYnqcBzg8sFXWVRnNQmYTaYCneSGSsSg2FMe2a1Q+c61LjwsrvmwgC/AK4SYUCBjNU1YHuDuO//xgUHW7VDBcdsoWjmuEKF+zFB0g8vJDrkjEK7FNHsef7MW1yWCkjkxb35QuqvJXM04RyIS5EEU8HGuw+4k4EAWF7z+/Y5M9YZwBv7La9iS50p4eA0VKF6ROc5gXku0gxDNmRlTjHCOr+mgaCQ7SHSEN6eUyW3M9+KjN8uzqGfk6FAHavYT0fblzK5cfYa4WwxH0XWwHUBF+WMZdhyT3fVlBbPdhdUy0SEN/5xgwG1tMqILJXJOPSKqD0fTc+fmmFJ9SU9GAHh8ojYjTFQVFFJah5sC0Jz+de5T9b2SgZIh+xQyMbhtZVoII7bQVF2nuy6RiKvrgJqjmhQ== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Thu, 06 Apr 2023 11:17:12 +0900 Jaewon Kim wrote: > >> + if (len / PAGE_SIZE > totalram_pages()) > >> + return ERR_PTR(-ENOMEM); > > > >We're catering for a buggy caller here, aren't we? Are such large > >requests ever reasonable? > > > >How about we decide what's the largest reasonable size and do a > >WARN_ON(larger-than-that), so the buggy caller gets fixed? > > Yes we're considering a buggy caller. I thought even totalram_pages() / 2 in > the old ion system is also unreasonable. To avoid the /2, I changed it to > totalram_pages() though. > > Because userspace can request that size repeately, I think WARN_ON() may be > called to too often, so that it would fill the kernel log buffer. Oh geeze. I trust that userspace needs elevated privileges of some form? If so, then spamming dmesg isn't an issue - root can do much worse than that. > Even we think WARN_ON_ONCE rather than WARN_ON, the buggy point is not kernel > layer. Unlike page fault mechanism, this dma-buf system heap gets the size from > userspace, and it is allowing unlimited size. I think we can't fix the buggy > user space with the kernel warning log. So I think warning is not enough, > and we need a safeguard in kernel layer. I really dislike that ram/2 thing - it's so arbitrary, hence is surely wrong for all cases. Is there something more thoughtful we can do? I mean, top priority here is to inform userspace that it's buggy so that it gets fixed (assuming this requires elevated privileges). And userspace which requests (totalram_pages()/2 - 1) bytes is still buggy, but we did nothing to get the bug fixed.