Remove RAND_set_urandom_fd.

Also update the documentation for RAND_enable_fork_unsafe_buffering. The
fd parameter is no longer used.

Update-Note: RAND_set_urandom_fd no longer exists. This was only called
by Chromium, which now uses CRYPTO_pre_sandbox_init.

Change-Id: I1659c1cc84a6f1edc01f6105fc07e80856e457fc
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/41424
Reviewed-by: Adam Langley <agl@google.com>
Commit-Queue: David Benjamin <davidben@google.com>

crypto/fipsmodule/rand/urandom.c

diff --git a/crypto/fipsmodule/rand/urandom.c b/crypto/fipsmodule/rand/urandom.c
index bf15eda..bae3fc3 100644
--- a/crypto/fipsmodule/rand/urandom.c
+++ b/crypto/fipsmodule/rand/urandom.c
@@ -95,17 +95,10 @@
 
 #endif  // USE_NR_getrandom
 
-// rand_lock is used to protect the |*_requested| variables.
-DEFINE_STATIC_MUTEX(rand_lock)
-
-// The following constants are magic values of |urandom_fd|.
-static const int kUnset = 0;
+// kHaveGetrandom in |urandom_fd| signals that |getrandom| or |getentropy| is
+// available and should be used instead.
 static const int kHaveGetrandom = -3;
 
-// urandom_fd_requested is set by |RAND_set_urandom_fd|. It's protected by
-// |rand_lock|.
-DEFINE_BSS_GET(int, urandom_fd_requested)
-
 // urandom_fd is a file descriptor to /dev/urandom. It's protected by |once|.
 DEFINE_BSS_GET(int, urandom_fd)
 
@@ -144,14 +137,9 @@
 DEFINE_STATIC_ONCE(rand_once)
 
 // init_once initializes the state of this module to values previously
-// requested. This is the only function that modifies |urandom_fd| and
-// |urandom_buffering|, whose values may be read safely after calling the
-// once.
+// requested. This is the only function that modifies |urandom_fd|, which may be
+// read safely after calling the once.
 static void init_once(void) {
-  CRYPTO_STATIC_MUTEX_lock_read(rand_lock_bss_get());
-  int fd = *urandom_fd_requested_bss_get();
-  CRYPTO_STATIC_MUTEX_unlock_read(rand_lock_bss_get());
-
 #if defined(USE_NR_getrandom)
   int have_getrandom;
   uint8_t dummy;
@@ -194,31 +182,16 @@
   abort();
 #endif
 
-  if (fd == kUnset) {
-    do {
-      fd = open("/dev/urandom", O_RDONLY);
-    } while (fd == -1 && errno == EINTR);
-  }
+  int fd;
+  do {
+    fd = open("/dev/urandom", O_RDONLY);
+  } while (fd == -1 && errno == EINTR);
 
   if (fd < 0) {
     perror("failed to open /dev/urandom");
     abort();
   }
 
-  assert(kUnset == 0);
-  if (fd == kUnset) {
-    // Because we want to keep |urandom_fd| in the BSS, we have to initialise
-    // it to zero. But zero is a valid file descriptor too. Thus if open
-    // returns zero for /dev/urandom, we dup it to get a non-zero number.
-    fd = dup(fd);
-    close(kUnset);
-
-    if (fd <= 0) {
-      perror("failed to dup /dev/urandom fd");
-      abort();
-    }
-  }
-
   int flags = fcntl(fd, F_GETFD);
   if (flags == -1) {
     // Native Client doesn't implement |fcntl|.
@@ -307,40 +280,6 @@
 #endif  // BORINGSSL_FIPS
 }
 
-void RAND_set_urandom_fd(int fd) {
-  fd = dup(fd);
-  if (fd < 0) {
-    perror("failed to dup supplied urandom fd");
-    abort();
-  }
-
-  assert(kUnset == 0);
-  if (fd == kUnset) {
-    // Because we want to keep |urandom_fd| in the BSS, we have to initialise
-    // it to zero. But zero is a valid file descriptor too. Thus if dup
-    // returned zero we dup it again to get a non-zero number.
-    fd = dup(fd);
-    close(kUnset);
-
-    if (fd <= 0) {
-      perror("failed to dup supplied urandom fd");
-      abort();
-    }
-  }
-
-  CRYPTO_STATIC_MUTEX_lock_write(rand_lock_bss_get());
-  *urandom_fd_requested_bss_get() = fd;
-  CRYPTO_STATIC_MUTEX_unlock_write(rand_lock_bss_get());
-
-  CRYPTO_init_sysrand();
-  if (*urandom_fd_bss_get() == kHaveGetrandom) {
-    close(fd);
-  } else if (*urandom_fd_bss_get() != fd) {
-    fprintf(stderr, "RAND_set_urandom_fd called after initialisation.\n");
-    abort();
-  }
-}
-
 // fill_with_entropy writes |len| bytes of entropy into |out|. It returns one
 // on success and zero on error. If |block| is one, this function will block
 // until the entropy pool is initialized. Otherwise, this function may fail,

include/openssl/rand.h

diff --git a/include/openssl/rand.h b/include/openssl/rand.h
index 5d02e12..4847eb7 100644
--- a/include/openssl/rand.h
+++ b/include/openssl/rand.h
@@ -36,26 +36,12 @@
 // Obscure functions.
 
 #if !defined(OPENSSL_WINDOWS)
-// RAND_set_urandom_fd causes the module to use a copy of |fd| for system
-// randomness rather opening /dev/urandom internally. The caller retains
-// ownership of |fd| and is at liberty to close it at any time. This is useful
-// if, due to a sandbox, /dev/urandom isn't available. If used, it must be
-// called before the first call to |RAND_bytes|, and it is mutually exclusive
-// with |RAND_enable_fork_unsafe_buffering|.
-//
-// |RAND_set_urandom_fd| does not buffer any entropy, so it is safe to call
-// |fork| at any time after calling |RAND_set_urandom_fd|.
-OPENSSL_EXPORT void RAND_set_urandom_fd(int fd);
-
 // RAND_enable_fork_unsafe_buffering enables efficient buffered reading of
 // /dev/urandom. It adds an overhead of a few KB of memory per thread. It must
-// be called before the first call to |RAND_bytes| and it is mutually exclusive
-// with calls to |RAND_set_urandom_fd|.
+// be called before the first call to |RAND_bytes|.
 //
-// If |fd| is non-negative then a copy of |fd| will be used rather than opening
-// /dev/urandom internally. Like |RAND_set_urandom_fd|, the caller retains
-// ownership of |fd|. If |fd| is negative then /dev/urandom will be opened and
-// any error from open(2) crashes the address space.
+// |fd| must be -1. We no longer support setting the file descriptor with this
+// function.
 //
 // It has an unusual name because the buffer is unsafe across calls to |fork|.
 // Hence, this function should never be called by libraries.