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Mon, 19 Nov 2018 21:26:11 -0800 (PST) From: "Joel Fernandes (Google)" To: linux-man@vger.kernel.org Cc: "Joel Fernandes (Google)" , Andrew Morton , Andy Lutomirski , Hugh Dickins , Jann Horn , John Stultz , linux-api@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-mm@kvack.org, =?UTF-8?q?Marc-Andr=C3=A9=20Lureau?= , Matthew Wilcox , Mike Kravetz , Shuah Khan , Stephen Rothwell Subject: [PATCH -manpage 1/2] fcntl.2: Update manpage with new memfd F_SEAL_FUTURE_WRITE seal Date: Mon, 19 Nov 2018 21:25:44 -0800 Message-Id: <20181120052545.76560-1-joel@joelfernandes.org> X-Mailer: git-send-email 2.19.1.1215.g8438c0b245-goog MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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) --- man2/fcntl.2 | 15 +++++++++++++++ 1 file changed, 15 insertions(+) diff --git a/man2/fcntl.2 b/man2/fcntl.2 index 03533d65b49d..54772f94964c 100644 --- a/man2/fcntl.2 +++ b/man2/fcntl.2 @@ -1525,6 +1525,21 @@ Furthermore, if there are any asynchronous I/O operations .RB ( io_submit (2)) pending on the file, all outstanding writes will be discarded. +.TP +.BR F_SEAL_FUTURE_WRITE +If this seal is set, the contents of the file can be modified only from +existing writeable mappings that were created prior to the seal being set. +Any attempt to create a new writeable mapping on the memfd via +.BR mmap (2) +will fail with +.BR EPERM. +Also any attempts to write to the memfd via +.BR write (2) +will fail with +.BR EPERM. +This is useful in situations where existing writable mapped regions need to be +kept intact while preventing any future writes. For example, to share a +read-only memory buffer to other processes that only the sender can write to. .\" .SS File read/write hints Write lifetime hints can be used to inform the kernel about the relative -- 2.19.1.1215.g8438c0b245-goog