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([2001:a61:251f:d701:c8c9:6ecf:205c:abb7]) by smtp.gmail.com with ESMTPSA id h13sm8318098wrw.54.2020.02.08.03.58.33 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 08 Feb 2020 03:58:33 -0800 (PST) Cc: mtk.manpages@gmail.com, Andrew Morton , Andy Lutomirski , dancol@google.com, Jann Horn , John Stultz , kernel-team@android.com, linux-api@vger.kernel.org, linux-man@vger.kernel.org, linux-mm@kvack.org, Matthew Wilcox , Mike Kravetz , Shuah Khan , Stephen Rothwell Subject: Re: [PATCH -manpage 2/2] memfd_create.2: Update manpage with new memfd F_SEAL_FUTURE_WRITE seal To: "Joel Fernandes (Google)" , linux-kernel@vger.kernel.org References: <20190314214844.207430-1-joel@joelfernandes.org> <20190314214844.207430-3-joel@joelfernandes.org> From: "Michael Kerrisk (man-pages)" Message-ID: <3349d0f2-6ea0-4e3a-1d9b-5a105edc34c8@gmail.com> Date: Sat, 8 Feb 2020 12:58:33 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.3.1 MIME-Version: 1.0 In-Reply-To: <20190314214844.207430-3-joel@joelfernandes.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello Joel, On 3/14/19 10:48 PM, Joel Fernandes (Google) wrote: > More details of the seal can be found in the LKML patch: > https://lore.kernel.org/lkml/20181120052137.74317-1-joel@joelfernandes.org/T/#t > > Signed-off-by: Joel Fernandes (Google) Thanks! Patch applied Cheers, Michael > --- > man2/memfd_create.2 | 15 ++++++++++++++- > 1 file changed, 14 insertions(+), 1 deletion(-) > > diff --git a/man2/memfd_create.2 b/man2/memfd_create.2 > index 15b1362f5525..3b7f032407ed 100644 > --- a/man2/memfd_create.2 > +++ b/man2/memfd_create.2 > @@ -280,7 +280,15 @@ in order to restrict further modifications on the file. > (If placing the seal > .BR F_SEAL_WRITE , > then it will be necessary to first unmap the shared writable mapping > -created in the previous step.) > +created in the previous step. Otherwise, behavior similar to > +.BR F_SEAL_WRITE > +can be achieved, by using > +.BR F_SEAL_FUTURE_WRITE > +which will prevent future writes via > +.BR mmap (2) > +and > +.BR write (2) > +from succeeding, while keeping existing shared writable mappings). > .IP 4. > A second process obtains a file descriptor for the > .BR tmpfs (5) > @@ -425,6 +433,7 @@ main(int argc, char *argv[]) > fprintf(stderr, "\et\etg \- F_SEAL_GROW\en"); > fprintf(stderr, "\et\ets \- F_SEAL_SHRINK\en"); > fprintf(stderr, "\et\etw \- F_SEAL_WRITE\en"); > + fprintf(stderr, "\et\etW \- F_SEAL_FUTURE_WRITE\en"); > fprintf(stderr, "\et\etS \- F_SEAL_SEAL\en"); > exit(EXIT_FAILURE); > } > @@ -463,6 +472,8 @@ main(int argc, char *argv[]) > seals |= F_SEAL_SHRINK; > if (strchr(seals_arg, \(aqw\(aq) != NULL) > seals |= F_SEAL_WRITE; > + if (strchr(seals_arg, \(aqW\(aq) != NULL) > + seals |= F_SEAL_FUTURE_WRITE; > if (strchr(seals_arg, \(aqS\(aq) != NULL) > seals |= F_SEAL_SEAL; > > @@ -518,6 +529,8 @@ main(int argc, char *argv[]) > printf(" GROW"); > if (seals & F_SEAL_WRITE) > printf(" WRITE"); > + if (seals & F_SEAL_FUTURE_WRITE) > + printf(" FUTURE_WRITE"); > if (seals & F_SEAL_SHRINK) > printf(" SHRINK"); > printf("\en"); > -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Linux/UNIX System Programming Training: http://man7.org/training/