[PATCH v3] mm/memfd: Add write seals when apply SEAL_EXEC to executable memfd

[jeffxu@chromium.org]

From: Jeff Xu <jeffxu@chromium.org>

When apply F_SEAL_EXEC to an executable memfd, add write seals also to
prevent modification of memfd.

Signed-off-by: Jeff Xu <jeffxu@chromium.org>
---
 mm/memfd.c                                 |  3 +++
 tools/testing/selftests/memfd/memfd_test.c | 25 ++++++++++++++++++++++
 2 files changed, 28 insertions(+)

diff --git a/mm/memfd.c b/mm/memfd.c
index 96dcfbfed09e..3a04c0698957 100644
--- a/mm/memfd.c
+++ b/mm/memfd.c
@@ -222,6 +222,9 @@ static int memfd_add_seals(struct file *file, unsigned int seals)
 		}
 	}
 
+	if (seals & F_SEAL_EXEC && inode->i_mode & 0111)
+		seals |= F_ALL_SEALS;
+
 	*file_seals |= seals;
 	error = 0;
 
diff --git a/tools/testing/selftests/memfd/memfd_test.c b/tools/testing/selftests/memfd/memfd_test.c
index 775c9e6c061e..0731e5b3cdce 100644
--- a/tools/testing/selftests/memfd/memfd_test.c
+++ b/tools/testing/selftests/memfd/memfd_test.c
@@ -32,6 +32,13 @@
 #define F_SEAL_EXEC	0x0020
 #endif
 
+#define F_ALL_SEALS (F_SEAL_SEAL | \
+		     F_SEAL_SHRINK | \
+		     F_SEAL_GROW | \
+		     F_SEAL_WRITE | \
+		     F_SEAL_FUTURE_WRITE | \
+		     F_SEAL_EXEC)
+
 #ifndef MAX_PATH
 #define MAX_PATH 256
 #endif
@@ -1006,6 +1013,7 @@ static void test_exec_seal(void)
 
 	printf("%s SEAL-EXEC\n", memfd_str);
 
+	printf("%s	Apply SEAL_EXEC\n", memfd_str);
 	fd = mfd_assert_new("kern_memfd_seal_exec",
 			    mfd_def_size,
 			    MFD_CLOEXEC | MFD_ALLOW_SEALING | MFD_EXEC);
@@ -1024,7 +1032,24 @@ static void test_exec_seal(void)
 	mfd_fail_chmod(fd, 0700);
 	mfd_fail_chmod(fd, 0100);
 	mfd_assert_chmod(fd, 0666);
+	mfd_assert_write(fd);
+	close(fd);
+
+	printf("%s	Apply ALL_SEALS\n", memfd_str);
+	fd = mfd_assert_new("kern_memfd_seal_exec",
+			    mfd_def_size,
+			    MFD_CLOEXEC | MFD_ALLOW_SEALING | MFD_EXEC);
 
+	mfd_assert_mode(fd, 0777);
+	mfd_assert_chmod(fd, 0700);
+
+	mfd_assert_has_seals(fd, 0);
+	mfd_assert_add_seals(fd, F_SEAL_EXEC);
+	mfd_assert_has_seals(fd, F_ALL_SEALS);
+
+	mfd_fail_chmod(fd, 0711);
+	mfd_fail_chmod(fd, 0600);
+	mfd_fail_write(fd);
 	close(fd);
 }
 
-- 
2.39.0.rc0.267.gcb52ba06e7-goog