mm/memfd: MFD_NOEXEC for memfd_create

Basic tests to ensure that user/group/other execute bits cannot be changed after applying F_SEAL_EXEC to a memfd.

Signed-off-by Daniel Verkamp <[email protected]>

---
  tools/testing/selftests/memfd/memfd_test.c | 80 ++++++++++++++++++++++
  1 file changed, 80 insertions(+)

tools/testing/selftests/memfd/memfd_test.c +4 -0

index 94df2692e6e4..fdb0e46e9df9 100644
@@ -28,6 +28,10 @@
  #define MFD_DEF_SIZE 8192
  #define STACK_SIZE 65536
 
+#ifndef F_SEAL_EXEC
+#define F_SEAL_EXEC	0x0020
+#endif
+
  /*
   * Default is not to test hugetlbfs
   */

tools/testing/selftests/memfd/memfd_test.c +40 -0

+		abort();
+	}
+
+	/* verify that file mode bits did not change */
+	mfd_assert_mode(fd, st.st_mode & 07777);
+}
+
  static int idle_thread_fn(void *arg)
  {
  	sigset_t set;

@@ -880,6 +926,39 @@ static void test_seal_resize(void)
  	close(fd);
  }
 
+/*
+ * Test SEAL_EXEC
+ * Test that chmod() cannot change x bits after sealing
+ */
+static void test_seal_exec(void)
+{
+	int fd;
+
+	printf("%s SEAL-EXEC\n", memfd_str);
+
+	fd = mfd_assert_new("kern_memfd_seal_exec",
+			    mfd_def_size,
+			    MFD_CLOEXEC | MFD_ALLOW_SEALING);
+
+	mfd_assert_mode(fd, 0777);
+
+	mfd_assert_chmod(fd, 0644);
+
+	mfd_assert_has_seals(fd, 0);
+	mfd_assert_add_seals(fd, F_SEAL_EXEC);
+	mfd_assert_has_seals(fd, F_SEAL_EXEC);
+
+	mfd_assert_chmod(fd, 0600);
+	mfd_fail_chmod(fd, 0777);
+	mfd_fail_chmod(fd, 0670);
+	mfd_fail_chmod(fd, 0605);
+	mfd_fail_chmod(fd, 0700);
+	mfd_fail_chmod(fd, 0100);
+	mfd_assert_chmod(fd, 0666);
+
+	close(fd);
+}
+
  /*
   * Test sharing via dup()
   * Test that seals are shared between dupped FDs and they're all equal.

tools/testing/selftests/memfd/memfd_test.c static void test_seal_exec(void) · line 1026

Quoted 4 lines

+ /* Create with NOEXEC and ALLOW_SEALING */
+ fd = mfd_assert_new("kern_memfd_noexec",

tools/testing/selftests/memfd/memfd_test.c +2 -0

+    mfd_def_size,
+    MFD_CLOEXEC | MFD_ALLOW_SEALING | MFD_NOEXEC);

Don't we need to check fd here?

From: Daniel Verkamp <[email protected]>

Tests that ensure MFD_NOEXEC memfds have the appropriate mode bits and cannot be chmod-ed into being executable.

Co-developed-by Jeff Xu <[email protected]>

Signed-off-by Jeff Xu <[email protected]>

Signed-off-by Daniel Verkamp <[email protected]>

---
 tools/testing/selftests/memfd/memfd_test.c | 34 ++++++++++++++++++++++
 1 file changed, 34 insertions(+)

tools/testing/selftests/memfd/memfd_test.c +34 -1

index 1d7e7b36bbdd..4906f778564e 100644
@@ -36,6 +36,10 @@
 #define MAX_PATH 256
 #endif
 
+#ifndef MFD_NOEXEC
+#define MFD_NOEXEC     0x0008U
+#endif
+
 /*
  * Default is not to test hugetlbfs
  */

@@ -1006,6 +1010,35 @@ static void test_seal_exec(void)
        close(fd);
 }
 
+/*
+ * Test memfd_create with MFD_NOEXEC flag
+ * Test that MFD_NOEXEC applies F_SEAL_EXEC and prevents change of exec bits
+ */
+static void test_noexec(void)
+{
+       int fd;
+
+       printf("%s NOEXEC\n", memfd_str);
+
+       /* Create with NOEXEC and ALLOW_SEALING */
+       fd = mfd_assert_new("kern_memfd_noexec",
+                           mfd_def_size,
+                           MFD_CLOEXEC | MFD_ALLOW_SEALING | MFD_NOEXEC);
+       mfd_assert_mode(fd, 0666);
+       mfd_assert_has_seals(fd, F_SEAL_EXEC);
+       mfd_fail_chmod(fd, 0777);
+       close(fd);
+
+       /* Create with NOEXEC but without ALLOW_SEALING */
+       fd = mfd_assert_new("kern_memfd_noexec",
+                           mfd_def_size,
+                           MFD_CLOEXEC | MFD_NOEXEC);
+       mfd_assert_mode(fd, 0666);
+       mfd_assert_has_seals(fd, F_SEAL_EXEC | F_SEAL_SEAL);
+       mfd_fail_chmod(fd, 0777);
+       close(fd);
+}
+
 /*
  * Test sharing via dup()
  * Test that seals are shared between dupped FDs and they're all equal.

@@ -1179,6 +1212,7 @@ int main(int argc, char **argv)
 
        test_create();
        test_basic();
+       test_noexec();
 
        test_seal_write();
        test_seal_future_write();
--

2.37.1.455.g008518b4e5-goog

From: Daniel Verkamp <[email protected]>

Basic tests to ensure that user/group/other execute bits cannot be changed after applying F_SEAL_EXEC to a memfd.

Co-developed-by Jeff Xu <[email protected]>

Signed-off-by Jeff Xu <[email protected]>

Signed-off-by Daniel Verkamp <[email protected]>

---
 tools/testing/selftests/memfd/memfd_test.c | 129 ++++++++++++++++++++-
 1 file changed, 128 insertions(+), 1 deletion(-)

tools/testing/selftests/memfd/memfd_test.c +94 -1

index 94df2692e6e4..1d7e7b36bbdd 100644
@@ -28,12 +28,44 @@
 #define MFD_DEF_SIZE 8192
 #define STACK_SIZE 65536
 
+#ifndef F_SEAL_EXEC
+#define F_SEAL_EXEC    0x0020
+#endif
+
+#ifndef MAX_PATH
+#define MAX_PATH 256
+#endif
+
 /*
  * Default is not to test hugetlbfs
  */
 static size_t mfd_def_size = MFD_DEF_SIZE;
 static const char *memfd_str = MEMFD_STR;
 
+static ssize_t fd2name(int fd, char *buf, size_t bufsize)
+{
+       char buf1[MAX_PATH];
+       int size;
+       ssize_t nbytes;
+
+       size = snprintf(buf1, MAX_PATH, "/proc/self/fd/%d", fd);
+       if (size < 0) {
+               printf("snprintf(%d) failed on %m\n", fd);
+               abort();
+       }
+
+       /*
+        * reserver one byte for string termination.
+        */
+       nbytes = readlink(buf1, buf, bufsize-1);
+       if (nbytes == -1) {
+               printf("readlink(%s) failed %m\n", buf1);
+               abort();
+       }
+       buf[nbytes] = '\0';
+       return nbytes;
+}
+
 static int mfd_assert_new(const char *name, loff_t sz, unsigned int flags)
 {
        int r, fd;

@@ -98,11 +130,14 @@ static unsigned int mfd_assert_get_seals(int fd)
 
 static void mfd_assert_has_seals(int fd, unsigned int seals)
 {
+       char buf[MAX_PATH];
+       int nbytes;
        unsigned int s;
+       fd2name(fd, buf, MAX_PATH);
 
        s = mfd_assert_get_seals(fd);
        if (s != seals) {
-               printf("%u != %u = GET_SEALS(%d)\n", seals, s, fd);
+               printf("%u != %u = GET_SEALS(%s)\n", seals, s, buf);
                abort();
        }
 }

@@ -594,6 +629,64 @@ static void mfd_fail_grow_write(int fd)
        }
 }
 
+static void mfd_assert_mode(int fd, int mode)
+{
+       struct stat st;
+       char buf[MAX_PATH];
+       int nbytes;
+
+       fd2name(fd, buf, MAX_PATH);
+
+       if (fstat(fd, &st) < 0) {
+               printf("fstat(%s) failed: %m\n", buf);
+               abort();
+       }
+
+       if ((st.st_mode & 07777) != mode) {
+               printf("fstat(%s) wrong file mode 0%04o, but expected
 0%04o\n",
+                      buf, (int)st.st_mode & 07777, mode);
+               abort();
+       }
+}
+
+static void mfd_assert_chmod(int fd, int mode)
+{
+       char buf[MAX_PATH];
+       int nbytes;
+
+       fd2name(fd, buf, MAX_PATH);
+
+       if (fchmod(fd, mode) < 0) {
+               printf("fchmod(%s, 0%04o) failed: %m\n", buf, mode);
+               abort();
+       }
+
+       mfd_assert_mode(fd, mode);
+}
+
+static void mfd_fail_chmod(int fd, int mode)
+{
+       struct stat st;
+       char buf[MAX_PATH];
+       int nbytes;
+
+       fd2name(fd, buf, MAX_PATH);
+
+       if (fstat(fd, &st) < 0) {
+               printf("fstat(%s) failed: %m\n", buf);
+               abort();
+       }
+
+       if (fchmod(fd, mode) == 0) {
+               printf("fchmod(%s, 0%04o) didn't fail as expected\n",
+                      buf, mode);
+               abort();
+       }
+
+       /* verify that file mode bits did not change */
+       mfd_assert_mode(fd, st.st_mode & 07777);
+}
+
 static int idle_thread_fn(void *arg)
 {

        sigset_t set;

tools/testing/selftests/memfd/memfd_test.c +34 -1

@@ -880,6 +973,39 @@ static void test_seal_resize(void)
        close(fd);
 }
 
+/*
+ * Test SEAL_EXEC
+ * Test that chmod() cannot change x bits after sealing
+ */
+static void test_seal_exec(void)
+{
+       int fd;
+
+       printf("%s SEAL-EXEC\n", memfd_str);
+
+       fd = mfd_assert_new("kern_memfd_seal_exec",
+                           mfd_def_size,
+                           MFD_CLOEXEC | MFD_ALLOW_SEALING);
+
+       mfd_assert_mode(fd, 0777);
+
+       mfd_assert_chmod(fd, 0644);
+
+       mfd_assert_has_seals(fd, 0);
+       mfd_assert_add_seals(fd, F_SEAL_EXEC);
+       mfd_assert_has_seals(fd, F_SEAL_EXEC);
+
+       mfd_assert_chmod(fd, 0600);
+       mfd_fail_chmod(fd, 0777);
+       mfd_fail_chmod(fd, 0670);
+       mfd_fail_chmod(fd, 0605);
+       mfd_fail_chmod(fd, 0700);
+       mfd_fail_chmod(fd, 0100);
+       mfd_assert_chmod(fd, 0666);
+
+       close(fd);
+}
+
 /*
  * Test sharing via dup()
  * Test that seals are shared between dupped FDs and they're all equal.

@@ -1059,6 +1185,7 @@ int main(int argc, char **argv)
        test_seal_shrink();
        test_seal_grow();
        test_seal_resize();
+       test_seal_exec();
 
        test_share_dup("SHARE-DUP", "");
        test_share_mmap("SHARE-MMAP", "");
--

2.37.1.455.g008518b4e5-goog

From: Daniel Verkamp <[email protected]>

Basic tests to ensure that user/group/other execute bits cannot be changed after applying F_SEAL_EXEC to a memfd.

Co-developed-by Jeff Xu <[email protected]>

Signed-off-by Jeff Xu <[email protected]>

Signed-off-by Daniel Verkamp <[email protected]>

---
 tools/testing/selftests/memfd/memfd_test.c | 129 ++++++++++++++++++++-
 1 file changed, 128 insertions(+), 1 deletion(-)

tools/testing/selftests/memfd/memfd_test.c +128 -2

index 94df2692e6e4..1d7e7b36bbdd 100644
@@ -28,12 +28,44 @@
 #define MFD_DEF_SIZE 8192
 #define STACK_SIZE 65536
 
+#ifndef F_SEAL_EXEC
+#define F_SEAL_EXEC    0x0020
+#endif
+
+#ifndef MAX_PATH
+#define MAX_PATH 256
+#endif
+
 /*
  * Default is not to test hugetlbfs
  */
 static size_t mfd_def_size = MFD_DEF_SIZE;
 static const char *memfd_str = MEMFD_STR;
 
+static ssize_t fd2name(int fd, char *buf, size_t bufsize)
+{
+       char buf1[MAX_PATH];
+       int size;
+       ssize_t nbytes;
+
+       size = snprintf(buf1, MAX_PATH, "/proc/self/fd/%d", fd);
+       if (size < 0) {
+               printf("snprintf(%d) failed on %m\n", fd);
+               abort();
+       }
+
+       /*
+        * reserver one byte for string termination.
+        */
+       nbytes = readlink(buf1, buf, bufsize-1);
+       if (nbytes == -1) {
+               printf("readlink(%s) failed %m\n", buf1);
+               abort();
+       }
+       buf[nbytes] = '\0';
+       return nbytes;
+}
+
 static int mfd_assert_new(const char *name, loff_t sz, unsigned int flags)
 {
        int r, fd;

@@ -98,11 +130,14 @@ static unsigned int mfd_assert_get_seals(int fd)
 
 static void mfd_assert_has_seals(int fd, unsigned int seals)
 {
+       char buf[MAX_PATH];
+       int nbytes;
        unsigned int s;
+       fd2name(fd, buf, MAX_PATH);
 
        s = mfd_assert_get_seals(fd);
        if (s != seals) {
-               printf("%u != %u = GET_SEALS(%d)\n", seals, s, fd);
+               printf("%u != %u = GET_SEALS(%s)\n", seals, s, buf);
                abort();
        }
 }

@@ -594,6 +629,64 @@ static void mfd_fail_grow_write(int fd)
        }
 }
 
+static void mfd_assert_mode(int fd, int mode)
+{
+       struct stat st;
+       char buf[MAX_PATH];
+       int nbytes;
+
+       fd2name(fd, buf, MAX_PATH);
+
+       if (fstat(fd, &st) < 0) {
+               printf("fstat(%s) failed: %m\n", buf);
+               abort();
+       }
+
+       if ((st.st_mode & 07777) != mode) {
+               printf("fstat(%s) wrong file mode 0%04o, but expected 0%04o\n",
+                      buf, (int)st.st_mode & 07777, mode);
+               abort();
+       }
+}
+
+static void mfd_assert_chmod(int fd, int mode)
+{
+       char buf[MAX_PATH];
+       int nbytes;
+
+       fd2name(fd, buf, MAX_PATH);
+
+       if (fchmod(fd, mode) < 0) {
+               printf("fchmod(%s, 0%04o) failed: %m\n", buf, mode);
+               abort();
+       }
+
+       mfd_assert_mode(fd, mode);
+}
+
+static void mfd_fail_chmod(int fd, int mode)
+{
+       struct stat st;
+       char buf[MAX_PATH];
+       int nbytes;
+
+       fd2name(fd, buf, MAX_PATH);
+
+       if (fstat(fd, &st) < 0) {
+               printf("fstat(%s) failed: %m\n", buf);
+               abort();
+       }
+
+       if (fchmod(fd, mode) == 0) {
+               printf("fchmod(%s, 0%04o) didn't fail as expected\n",
+                      buf, mode);
+               abort();
+       }
+
+       /* verify that file mode bits did not change */
+       mfd_assert_mode(fd, st.st_mode & 07777);
+}
+
 static int idle_thread_fn(void *arg)
 {
        sigset_t set;

@@ -880,6 +973,39 @@ static void test_seal_resize(void)
        close(fd);
 }
 
+/*
+ * Test SEAL_EXEC
+ * Test that chmod() cannot change x bits after sealing
+ */
+static void test_seal_exec(void)
+{
+       int fd;
+
+       printf("%s SEAL-EXEC\n", memfd_str);
+
+       fd = mfd_assert_new("kern_memfd_seal_exec",
+                           mfd_def_size,
+                           MFD_CLOEXEC | MFD_ALLOW_SEALING);
+
+       mfd_assert_mode(fd, 0777);
+
+       mfd_assert_chmod(fd, 0644);
+
+       mfd_assert_has_seals(fd, 0);
+       mfd_assert_add_seals(fd, F_SEAL_EXEC);
+       mfd_assert_has_seals(fd, F_SEAL_EXEC);
+
+       mfd_assert_chmod(fd, 0600);
+       mfd_fail_chmod(fd, 0777);
+       mfd_fail_chmod(fd, 0670);
+       mfd_fail_chmod(fd, 0605);
+       mfd_fail_chmod(fd, 0700);
+       mfd_fail_chmod(fd, 0100);
+       mfd_assert_chmod(fd, 0666);
+
+       close(fd);
+}
+
 /*
  * Test sharing via dup()
  * Test that seals are shared between dupped FDs and they're all equal.

@@ -1059,6 +1185,7 @@ int main(int argc, char **argv)
        test_seal_shrink();
        test_seal_grow();
        test_seal_resize();
+       test_seal_exec();
 
        test_share_dup("SHARE-DUP", "");
        test_share_mmap("SHARE-MMAP", "");
--

2.37.1.455.g008518b4e5-goog

Tests that ensure MFD_NOEXEC memfds have the appropriate mode bits and cannot be chmod-ed into being executable.

Signed-off-by Daniel Verkamp <[email protected]>

---
  tools/testing/selftests/memfd/memfd_test.c | 34 ++++++++++++++++++++++
  1 file changed, 34 insertions(+)

tools/testing/selftests/memfd/memfd_test.c +8 -0

index fdb0e46e9df9..a79567161cdf 100644
@@ -32,6 +32,10 @@
  #define F_SEAL_EXEC	0x0020
  #endif
 
+#ifndef MFD_NOEXEC
+#define MFD_NOEXEC	0x0008U
+#endif
+
  /*
   * Default is not to test hugetlbfs
   */

@@ -959,6 +963,35 @@ static void test_seal_exec(void)
  	close(fd);
  }
 
+/*
+ * Test memfd_create with MFD_NOEXEC flag
+ * Test that MFD_NOEXEC applies F_SEAL_EXEC and prevents change of exec bits
+ */

tools/testing/selftests/memfd/memfd_test.c +6 -0

+	mfd_assert_mode(fd, 0666);
+	mfd_assert_has_seals(fd, F_SEAL_EXEC | F_SEAL_SEAL);
+	mfd_fail_chmod(fd, 0777);
+	close(fd);
+}
+
  /*
   * Test sharing via dup()
   * Test that seals are shared between dupped FDs and they're all equal.