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Tsirkin" To: Matthew Wilcox Cc: "Vishal Moola (Oracle)" , David Hildenbrand , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton , Paul Moore , Stephen Smalley , Ondrej Mosnacek , selinux@vger.kernel.org Subject: Re: [PATCH v2 7/7] virtio_balloon: Stop calling page_address() in free_pages() Message-ID: <20250830074747-mutt-send-email-mst@kernel.org> References: <20250826205617.1032945-1-vishal.moola@gmail.com> <20250826205617.1032945-8-vishal.moola@gmail.com> <5ee2b684-94d9-40be-b01c-b0538ced33bc@redhat.com> MIME-Version: 1.0 In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: cfNngryrmGQTpyQ2XJafVUZuaVBeeK1zpjGF6d3H_7k_1756554504 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline X-Rspamd-Queue-Id: E23E84000D X-Stat-Signature: xduok5huawbssoqd4tbc1963upy7qc7h X-Rspam-User: X-Rspamd-Server: rspam06 X-HE-Tag: 1756554508-503662 X-HE-Meta: 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 ecZD07vy 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 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: List-Subscribe: List-Unsubscribe: On Thu, Aug 28, 2025 at 03:53:56PM +0100, Matthew Wilcox wrote: > On Wed, Aug 27, 2025 at 11:29:22AM -0700, Vishal Moola (Oracle) wrote: > > I imagine theres more of these lingering in the kernel, but theres so > > many callers and I only looked for the ones that were calling > > page_address() inline :(. > > There's only 841 callers of free_page() and free_pages()! > > It's a bit of a disease we have, to be honest, Almost all of > them should be using kmalloc() instead. To pick on one at random, > sel_read_bool() in security/selinux/selinuxfs.c is the implementation > of read() for some file in selinux. All it's trying to do is output two > numbers, so it allocates an entire page of memory, prints two numbers > to it (while being VERY CAREFUL not to overflow the buffer!) and copies > the buffer to userspace. > > It should just use kmalloc. Why even kmalloc? Why not have a small array on stack? > Oh, and it should avoid leaking the buffer > if security_get_bool_value() returns an error.