From: "Joel Fernandes (Google)" <joel@joelfernandes.org>
To: linux-man@vger.kernel.org
Cc: "Joel Fernandes (Google)" <joel@joelfernandes.org>,
"Andrew Morton" <akpm@linux-foundation.org>,
"Andy Lutomirski" <luto@kernel.org>,
dancol@google.com, "Hugh Dickins" <hughd@google.com>,
"Jann Horn" <jannh@google.com>,
"John Stultz" <john.stultz@linaro.org>,
linux-api@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-mm@kvack.org,
"Marc-André Lureau" <marcandre.lureau@redhat.com>,
"Matthew Wilcox" <willy@infradead.org>,
"Mike Kravetz" <mike.kravetz@oracle.com>,
"Shuah Khan" <shuah@kernel.org>,
"Stephen Rothwell" <sfr@canb.auug.org.au>
Subject: [PATCH -manpage 2/2] memfd_create.2: Update manpage with new memfd F_SEAL_FUTURE_WRITE seal
Date: Wed, 12 Dec 2018 14:05:14 -0800 [thread overview]
Message-ID: <20181212220514.205269-2-joel@joelfernandes.org> (raw)
In-Reply-To: <20181212220514.205269-1-joel@joelfernandes.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) <joel@joelfernandes.org>
---
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 3cd392d1b4d9..fce2bf8d0fff 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, "\\t\\tg \- F_SEAL_GROW\\n");
fprintf(stderr, "\\t\\ts \- F_SEAL_SHRINK\\n");
fprintf(stderr, "\\t\\tw \- F_SEAL_WRITE\\n");
+ fprintf(stderr, "\\t\\tW \- F_SEAL_FUTURE_WRITE\\n");
fprintf(stderr, "\\t\\tS \- F_SEAL_SEAL\\n");
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("\\n");
--
2.20.0.rc1.387.gf8505762e3-goog
next prev parent reply other threads:[~2018-12-12 22:05 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-12-12 22:05 [PATCH -manpage 1/2] fcntl.2: Update manpage with new memfd F_SEAL_FUTURE_WRITE seal Joel Fernandes (Google)
2018-12-12 22:05 ` Joel Fernandes (Google) [this message]
-- strict thread matches above, loose matches on Subject: below --
2019-03-14 21:48 [PATCH -manpage 0/2] Joel Fernandes (Google)
2019-03-14 21:48 ` [PATCH -manpage 2/2] memfd_create.2: Update manpage with new memfd F_SEAL_FUTURE_WRITE seal Joel Fernandes (Google)
2020-02-08 11:58 ` Michael Kerrisk (man-pages)
2019-01-13 0:14 [PATCH -manpage 0/2] Document " Joel Fernandes
2019-01-13 0:14 ` [PATCH -manpage 2/2] memfd_create.2: Update manpage with new " Joel Fernandes
2018-11-20 5:25 [PATCH -manpage 1/2] fcntl.2: " Joel Fernandes (Google)
2018-11-20 5:25 ` [PATCH -manpage 2/2] memfd_create.2: " Joel Fernandes (Google)
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