random: fix seeding with zero entropy

Add data from zero-entropy random_writes directly to output pools to
avoid accounting difficulties on machines without entropy sources.

Tested on lguest with all entropy sources disabled.

Signed-off-by: Matt Mackall <mpm@selenic.com>
Acked-by: "Theodore Ts'o" <tytso@mit.edu>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 31 insertions, 24 deletions

diff --git a/drivers/char/random.c b/drivers/char/random.c
index 9705b439448a..0474cac4a84e 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -1020,37 +1020,44 @@ random_poll(struct file *file, poll_table * wait)
         return mask;
 }
 
-static ssize_t
-random_write(struct file * file, const char __user * buffer,
-             size_t count, loff_t *ppos)
+static int
+write_pool(struct entropy_store *r, const char __user *buffer, size_t count)
 {
-        int ret = 0;
         size_t bytes;
         __u32 buf[16];
         const char __user *p = buffer;
-        size_t c = count;
 
-        while (c > 0) {
-                bytes = min(c, sizeof(buf));
+        while (count > 0) {
+                bytes = min(count, sizeof(buf));
+                if (copy_from_user(&buf, p, bytes))
+                        return -EFAULT;
 
-                bytes -= copy_from_user(&buf, p, bytes);
-                if (!bytes) {
-                        ret = -EFAULT;
-                        break;
-                }
-                c -= bytes;
+                count -= bytes;
                 p += bytes;
 
-                add_entropy_words(&input_pool, buf, (bytes + 3) / 4);
-        }
-        if (p == buffer) {
-                return (ssize_t)ret;
-        } else {
-                struct inode *inode = file->f_path.dentry->d_inode;
-                inode->i_mtime = current_fs_time(inode->i_sb);
-                mark_inode_dirty(inode);
-                return (ssize_t)(p - buffer);
+                add_entropy_words(r, buf, (bytes + 3) / 4);
         }
+
+        return 0;
+}
+
+static ssize_t
+random_write(struct file * file, const char __user * buffer,
+             size_t count, loff_t *ppos)
+{
+        size_t ret;
+        struct inode *inode = file->f_path.dentry->d_inode;
+
+        ret = write_pool(&blocking_pool, buffer, count);
+        if (ret)
+                return ret;
+        ret = write_pool(&nonblocking_pool, buffer, count);
+        if (ret)
+                return ret;
+
+        inode->i_mtime = current_fs_time(inode->i_sb);
+        mark_inode_dirty(inode);
+        return (ssize_t)count;
 }
 
 static int
@@ -1089,8 +1096,8 @@ random_ioctl(struct inode * inode, struct file * file,
                         return -EINVAL;
                 if (get_user(size, p++))
                         return -EFAULT;
-                retval = random_write(file, (const char __user *) p,
-                                      size, &file->f_pos);
+                retval = write_pool(&input_pool, (const char __user *)p,
+                                    size);
                 if (retval < 0)
                         return retval;
                 credit_entropy_store(&input_pool, ent_count);