Modify the DEVRANDOM source so that the files are kept open persistently.

This allows operation inside a chroot environment without having the
random device present.

A new call, RAND_keep_random_devices_open(), has been introduced that can
be used to control file descriptor use by the random seed sources. Some
seed sources maintain open file descriptors by default, which allows
such sources to operate in a chroot(2) jail without the associated device
nodes being available.

Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Matthias St. Pierre <Matthias.St.Pierre@ncp-e.com>
(Merged from https://github.com/openssl/openssl/pull/6432)

4 files changed, 197 insertions, 16 deletions

diff --git a/crypto/rand/rand_lib.c b/crypto/rand/rand_lib.c
index 1a9a7d2ce0..d31735c5c4 100644
--- a/crypto/rand/rand_lib.c
+++ b/crypto/rand/rand_lib.c
@@ -324,8 +324,13 @@ DEFINE_RUN_ONCE_STATIC(do_rand_init)
     if (rand_nonce_lock == NULL)
         goto err2;
 
+    if (!rand_pool_init())
+        goto err3;
+
     return 1;
 
+err3:
+    rand_pool_cleanup();
 err2:
     CRYPTO_THREAD_lock_free(rand_meth_lock);
     rand_meth_lock = NULL;
@@ -343,6 +348,7 @@ void rand_cleanup_int(void)
 
     if (meth != NULL && meth->cleanup != NULL)
         meth->cleanup();
+    rand_pool_cleanup();
     RAND_set_rand_method(NULL);
 #ifndef OPENSSL_NO_ENGINE
     CRYPTO_THREAD_lock_free(rand_engine_lock);
@@ -355,6 +361,15 @@ void rand_cleanup_int(void)
 }
 
 /*
+ * RAND_close_seed_files() ensures that any seed file decriptors are
+ * closed after use.
+ */
+void RAND_keep_random_devices_open(int keep)
+{
+    rand_pool_keep_random_devices_open(keep);
+}
+
+/*
  * RAND_poll() reseeds the default RNG using random input
  *
  * The random input is obtained from polling various entropy
diff --git a/crypto/rand/rand_unix.c b/crypto/rand/rand_unix.c
index a545e08d8c..b64cf27825 100644
--- a/crypto/rand/rand_unix.c
+++ b/crypto/rand/rand_unix.c
@@ -30,6 +30,8 @@
 
 #if defined(OPENSSL_SYS_UNIX) || defined(__DJGPP__)
 # include <sys/types.h>
+# include <sys/stat.h>
+# include <fcntl.h>
 # include <unistd.h>
 # include <sys/time.h>
 
@@ -154,6 +156,14 @@ size_t rand_pool_acquire_entropy(RAND_POOL *pool)
     return rand_pool_entropy_available(pool);
 }
 
+void rand_pool_cleanup(void)
+{
+}
+
+void rand_pool_keep_random_devices_open(int keep)
+{
+}
+
 # else
 
 #  if defined(OPENSSL_RAND_SEED_EGD) && \
@@ -274,6 +284,134 @@ int syscall_random(void *buf, size_t buflen)
     return -1;
 }
 
+#if  !defined(OPENSSL_RAND_SEED_NONE) && defined(OPENSSL_RAND_SEED_DEVRANDOM)
+static const char *random_device_paths[] = { DEVRANDOM };
+static struct random_device {
+    int fd;
+    dev_t dev;
+    ino_t ino;
+    mode_t mode;
+    dev_t rdev;
+} random_devices[OSSL_NELEM(random_device_paths)];
+static int keep_random_devices_open = 1;
+
+/*
+ * Verify that the file descriptor associated with the random source is
+ * still valid. The rationale for doing this is the fact that it is not
+ * uncommon for daemons to close all open file handles when daemonizing.
+ * So the handle might have been closed or even reused for opening
+ * another file.
+ */
+static int check_random_device(struct random_device * rd)
+{
+    struct stat st;
+
+    return rd->fd != -1
+           && fstat(rd->fd, &st) != -1
+           && rd->dev == st.st_dev
+           && rd->ino == st.st_ino
+           && ((rd->mode ^ st.st_mode) & ~(S_IRWXU | S_IRWXG | S_IRWXO)) == 0
+           && rd->rdev == st.st_rdev;
+}
+
+/*
+ * Open a random device if required and return its file descriptor or -1 on error
+ */
+static int get_random_device(size_t n)
+{
+    struct stat st;
+    struct random_device * rd = &random_devices[n];
+
+    /* reuse existing file descriptor if it is (still) valid */
+    if (check_random_device(rd))
+        return rd->fd;
+
+    /* open the random device ... */
+    if ((rd->fd = open(random_device_paths[n], O_RDONLY)) == -1)
+        return rd->fd;
+
+    /* ... and cache its relevant stat(2) data */
+    if (fstat(rd->fd, &st) != -1) {
+        rd->dev = st.st_dev;
+        rd->ino = st.st_ino;
+        rd->mode = st.st_mode;
+        rd->rdev = st.st_rdev;
+    } else {
+        close(rd->fd);
+        rd->fd = -1;
+    }
+
+    return rd->fd;
+}
+
+/*
+ * Close a random device making sure it is a random device
+ */
+static void close_random_device(size_t n)
+{
+    struct random_device * rd = &random_devices[n];
+
+    if (check_random_device(rd))
+        close(rd->fd);
+    rd->fd = -1;
+}
+
+static void open_random_devices(void)
+{
+    size_t i;
+
+    for (i = 0; i < OSSL_NELEM(random_devices); i++)
+        (void)get_random_device(i);
+}
+
+int rand_pool_init(void)
+{
+    size_t i;
+
+    for (i = 0; i < OSSL_NELEM(random_devices); i++)
+        random_devices[i].fd = -1;
+    open_random_devices();
+    return 1;
+}
+
+void rand_pool_cleanup(void)
+{
+    size_t i;
+
+    for (i = 0; i < OSSL_NELEM(random_devices); i++)
+        close_random_device(i);
+}
+
+void rand_pool_keep_random_devices_open(int keep)
+{
+    if (keep)
+        open_random_devices();
+    else
+        rand_pool_cleanup();
+    keep_random_devices_open = keep;
+}
+
+#  else     /* defined(OPENSSL_RAND_SEED_NONE)
+             * || !defined(OPENSSL_RAND_SEED_DEVRANDOM)
+             */
+
+int rand_pool_init(void)
+{
+    return 1;
+}
+
+void rand_pool_cleanup(void)
+{
+}
+
+void rand_pool_keep_random_devices_open(int keep)
+{
+}
+
+#  endif    /* !defined(OPENSSL_RAND_SEED_NONE)
+             * && defined(OPENSSL_RAND_SEED_DEVRANDOM)
+             */
+
 /*
  * Try the various seeding methods in turn, exit when successful.
  *
@@ -324,30 +462,33 @@ size_t rand_pool_acquire_entropy(RAND_POOL *pool)
 
 #   ifdef OPENSSL_RAND_SEED_DEVRANDOM
     bytes_needed = rand_pool_bytes_needed(pool, 1 /*entropy_factor*/);
-    if (bytes_needed > 0) {
-        static const char *paths[] = { DEVRANDOM, NULL };
-        FILE *fp;
-        int i;
+    {
+        size_t i;
 
-        for (i = 0; paths[i] != NULL; i++) {
-            if ((fp = fopen(paths[i], "rb")) == NULL)
+        for (i = 0; bytes_needed > 0 && i < OSSL_NELEM(random_device_paths); i++) {
+            const int fd = get_random_device(i);
+
+            if (fd == -1)
                 continue;
-            setbuf(fp, NULL);
             buffer = rand_pool_add_begin(pool, bytes_needed);
             if (buffer != NULL) {
-                size_t bytes = 0;
-                if (fread(buffer, 1, bytes_needed, fp) == bytes_needed)
-                    bytes = bytes_needed;
+                const ssize_t n = read(fd, buffer, bytes_needed);
 
-                rand_pool_add_end(pool, bytes, 8 * bytes);
-                entropy_available = rand_pool_entropy_available(pool);
+                if (n <= 0) {
+                    close_random_device(i);
+                    continue;
+                }
+
+                rand_pool_add_end(pool, n, 8 * n);
             }
-            fclose(fp);
-            if (entropy_available > 0)
-                return entropy_available;
+            if (!keep_random_devices_open)
+                close_random_device(i);
 
             bytes_needed = rand_pool_bytes_needed(pool, 1 /*entropy_factor*/);
         }
+        entropy_available = rand_pool_entropy_available(pool);
+        if (entropy_available > 0)
+            return entropy_available;
     }
 #   endif
 
@@ -433,7 +574,6 @@ int rand_pool_add_additional_data(RAND_POOL *pool)
 }
 
 
-
 /*
  * Get the current time with the highest possible resolution
  *
diff --git a/crypto/rand/rand_vms.c b/crypto/rand/rand_vms.c
index b263f94208..43dddf3c93 100644
--- a/crypto/rand/rand_vms.c
+++ b/crypto/rand/rand_vms.c
@@ -507,4 +507,17 @@ int rand_pool_add_additional_data(RAND_POOL *pool)
     return rand_pool_add(pool, (unsigned char *)&data, sizeof(data), 0);
 }
 
+int rand_pool_init(void)
+{
+    return 1;
+}
+
+void rand_pool_cleanup(void)
+{
+}
+
+void rand_pool_keep_random_devices_open(int keep)
+{
+}
+
 #endif
diff --git a/crypto/rand/rand_win.c b/crypto/rand/rand_win.c
index f2059eb412..34c2a8b924 100644
--- a/crypto/rand/rand_win.c
+++ b/crypto/rand/rand_win.c
@@ -169,4 +169,17 @@ void RAND_screen(void)
 }
 # endif
 
+int rand_pool_init(void)
+{
+    return 1;
+}
+
+void rand_pool_cleanup(void)
+{
+}
+
+void rand_pool_keep_random_devices_open(int keep)
+{
+}
+
 #endif