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

CHANGES

@@ -9,6 +9,13 @@
 
  Changes between 1.1.0h and 1.1.1 [xx XXX xxxx]
 
+  *) Modified the random device based seed sources to keep the relevant
+     file descriptors open rather than reopening them on each access.
+     This allows such sources to operate in a chroot() jail without
+     the associated device nodes being available. This behaviour can be
+     controlled using RAND_keep_random_devices_open().
+     [Paul Dale]
+
   *) Numerous side-channel attack mitigations have been applied. This may have
      performance impacts for some algorithms for the benefit of improved
      security. Specific changes are noted in this change log by their respective

crypto/include/internal/rand_int.h

@@ -111,4 +111,21 @@ int rand_pool_add_nonce_data(RAND_POOL *pool);
  */
 int rand_pool_add_additional_data(RAND_POOL *pool);
 
+/*
+ * Initialise the random pool reseeding sources.
+ *
+ * Returns 1 on success and 0 on failure.
+ */
+int rand_pool_init(void);
+
+/*
+ * Finalise the random pool reseeding sources.
+ */
+void rand_pool_cleanup(void);
+
+/*
+ * Control the random pool use of open file descriptors.
+ */
+void rand_pool_keep_random_devices_open(int keep);
+
 #endif

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);
@@ -354,6 +360,15 @@ void rand_cleanup_int(void)
     rand_nonce_lock = NULL;
 }
 
+/*
+ * 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
  *

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
  *

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

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

doc/man3/RAND_add.pod

@@ -2,7 +2,8 @@
 
 =head1 NAME
 
-RAND_add, RAND_poll, RAND_seed, RAND_status, RAND_event, RAND_screen
+RAND_add, RAND_poll, RAND_seed, RAND_status, RAND_event, RAND_screen,
+RAND_keep_random_devices_open
 - add randomness to the PRNG or get its status
 
 =head1 SYNOPSIS
@@ -15,6 +16,8 @@ RAND_add, RAND_poll, RAND_seed, RAND_status, RAND_event, RAND_screen
  void RAND_add(const void *buf, int num, double randomness);
  void RAND_seed(const void *buf, int num);
 
+ void RAND_keep_random_devices_open(int keep);
+
 Deprecated:
 
  #if OPENSSL_API_COMPAT < 0x10100000L
@@ -54,6 +57,15 @@ should consider using L<RAND_load_file(3)> instead.
 
 RAND_seed() is equivalent to RAND_add() with B<randomness> set to B<num>.
 
+RAND_keep_random_devices_open() is used to control file descriptor
+usage 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. When
+the B<keep> argument is zero, this call disables the retention of file
+descriptors. Conversely, a non-zero argument enables the retention of
+file descriptors. This function is usually called during initialization
+and it takes effect immediately.
+
 RAND_event() and RAND_screen() are equivalent to RAND_poll() and exist
 for compatibility reasons only. See HISTORY section below.
 

include/openssl/rand.h

@@ -44,6 +44,7 @@ int RAND_priv_bytes(unsigned char *buf, int num);
 DEPRECATEDIN_1_1_0(int RAND_pseudo_bytes(unsigned char *buf, int num))
 
 void RAND_seed(const void *buf, int num);
+void RAND_keep_random_devices_open(int keep);
 
 # if defined(__ANDROID__) && defined(__NDK_FPABI__)
 __NDK_FPABI__	/* __attribute__((pcs("aapcs"))) on ARM */

util/libcrypto.num

@@ -4568,3 +4568,4 @@ EVP_PKEY_get_raw_private_key            4519	1_1_1	EXIST::FUNCTION:
 EVP_PKEY_asn1_set_get_priv_key          4520	1_1_1	EXIST::FUNCTION:
 EVP_PKEY_asn1_set_get_pub_key           4521	1_1_1	EXIST::FUNCTION:
 EVP_PKEY_set_alias_type                 4522	1_1_1	EXIST::FUNCTION:
+RAND_keep_random_devices_open           4523	1_1_1	EXIST::FUNCTION: