rand/randfile.c: permit non-regular files in RAND_load_file.

Apparently applications rely on RAND_load_file's ability to work with
non-regular files, customarily with /dev/urandom, so that the ban was
not exactly appropriate.
Reviewed-by: NRich Salz <rsalz@openssl.org>
Reviewed-by: NBernd Edlinger <bernd.edlinger@hotmail.de>
Reviewed-by: NPaul Dale <paul.dale@oracle.com>
Reviewed-by: NTim Hudson <tjh@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/5737)

crypto/rand/randfile.c

@@ -32,6 +32,8 @@
 #  define chmod   _chmod
 #  define open    _open
 #  define fdopen  _fdopen
+#  define fstat   _fstat
+#  define fileno  _fileno
 # endif
 #endif
 
@@ -82,27 +84,45 @@ int RAND_load_file(const char *file, long bytes)
     if (bytes == 0)
         return 0;
 
-#ifndef OPENSSL_NO_POSIX_IO
-    if (stat(file, &sb) < 0 || !S_ISREG(sb.st_mode)) {
-        RANDerr(RAND_F_RAND_LOAD_FILE, RAND_R_NOT_A_REGULAR_FILE);
+    if ((in = openssl_fopen(file, "rb")) == NULL) {
+        RANDerr(RAND_F_RAND_LOAD_FILE, RAND_R_CANNOT_OPEN_FILE);
         ERR_add_error_data(2, "Filename=", file);
         return -1;
     }
-#endif
-    if ((in = openssl_fopen(file, "rb")) == NULL) {
-        RANDerr(RAND_F_RAND_LOAD_FILE, RAND_R_CANNOT_OPEN_FILE);
+
+#ifndef OPENSSL_NO_POSIX_IO
+    if (fstat(fileno(in), &sb) < 0) {
+        RANDerr(RAND_F_RAND_LOAD_FILE, RAND_R_INTERNAL_ERROR);
         ERR_add_error_data(2, "Filename=", file);
         return -1;
     }
 
+    if (!S_ISREG(sb.st_mode) && bytes < 0)
+        bytes = 256;
+#endif
+    /*
+     * Don't buffer, because even if |file| is regular file, we have
+     * no control over the buffer, so why would we want a copy of its
+     * contents lying around?
+     */
+    setbuf(in, NULL);
+
     for ( ; ; ) {
         if (bytes > 0)
             n = (bytes < RAND_FILE_SIZE) ? (int)bytes : RAND_FILE_SIZE;
         else
             n = RAND_FILE_SIZE;
         i = fread(buf, 1, n, in);
-        if (i <= 0)
+#ifdef EINTR
+        if (ferror(in) && errno == EINTR){
+            clearerr(in);
+            if (i == 0)
+                continue;
+        }
+#endif
+        if (i == 0)
             break;
+
         RAND_add(buf, i, (double)i);
         ret += i;
 

doc/man3/RAND_load_file.pod

@@ -24,6 +24,9 @@ Do not load the same file multiple times unless its contents have
 been updated by RAND_write_file() between reads.
 Also, note that B<filename> should be adequately protected so that an
 attacker cannot replace or examine the contents.
+If B<filename> is not a regular file, then user is considered to be
+responsible for any side effects, e.g. non-anticipated blocking or
+capture of controlling terminal.
 
 RAND_write_file() writes a number of random bytes (currently 128) to
 file B<filename> which can be used to initialize the PRNG by calling
@@ -70,13 +73,6 @@ error.
 
 L<RAND_bytes(3)>, L<RAND_add(3)>
 
-=head1 HISTORY
-
-A comment in the source since at least OpenSSL 1.0.2 said that
-RAND_load_file() and RAND_write_file() were only intended for regular files,
-and not really device special files such as C</dev/random>.  This was
-poorly enforced before OpenSSL 1.1.1.
-
 =head1 COPYRIGHT
 
 Copyright 2000-2017 The OpenSSL Project Authors. All Rights Reserved.