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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id p70sm226890pjp.47.2020.03.25.15.54.09 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 25 Mar 2020 15:54:10 -0700 (PDT) Date: Wed, 25 Mar 2020 15:54:09 -0700 From: Kees Cook To: "Eric W. Biederman" Cc: Vlastimil Babka , Luis Chamberlain , Iurii Zaikin , linux-kernel@vger.kernel.org, linux-api@vger.kernel.org, linux-mm@kvack.org, Ivan Teterevkov , Michal Hocko , David Rientjes , Matthew Wilcox , "Guilherme G . Piccoli" Subject: Re: [RFC v2 1/2] kernel/sysctl: support setting sysctl parameters from kernel command line Message-ID: <202003251544.7ECB392A7@keescook> References: <20200325120345.12946-1-vbabka@suse.cz> <874kuc5b5z.fsf@x220.int.ebiederm.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <874kuc5b5z.fsf@x220.int.ebiederm.org> 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 Wed, Mar 25, 2020 at 05:20:40PM -0500, Eric W. Biederman wrote: > Hmm. There is a big gotcha in here and I think it should be mentioned. > This code only works because no one has done set_fs(KERNEL_DS). Which > means this only works with strings that are kernel addresses essentially > by mistake. A big fat comment documenting why it is safe to pass in > kernel addresses to a function that takes a "char __user*" pointer > would be very good. Yeah, I was going to mention this too just now as I went looking through one of the handlers and was reminded that the args are marked __user. :P I suspect we might need to add some __force __user markings or something (with a comment as you say above), to keep sparse from going crazy. :) -- Kees Cook