hwrng: core - use per-rng quality value instead of global setting

The current_quality variable exposed as a module parameter is
fundamentally broken: If it is set at boot time, it is overwritten once
the first hw rng device is loaded; if it is set at runtime, it is
without effect if the hw rng device had its quality value set to 0 (and
no default_quality was set); and if a new rng is selected, it gets
overwritten. Therefore, mark it as obsolete, and replace it by the
per-rng quality setting.

Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

diff --git a/drivers/char/hw_random/core.c b/drivers/char/hw_random/core.c
index 29febf5..8df102b 100644 (file)
--- a/drivers/char/hw_random/core.c
+++ b/drivers/char/hw_random/core.c
@@ -44,14 +44,14 @@ static unsigned short default_quality; /* = 0; default to "off" */
 
 module_param(current_quality, ushort, 0644);
 MODULE_PARM_DESC(current_quality,
-                "current hwrng entropy estimation per 1024 bits of input");
+                "current hwrng entropy estimation per 1024 bits of input -- obsolete");
 module_param(default_quality, ushort, 0644);
 MODULE_PARM_DESC(default_quality,
                 "default entropy content of hwrng per 1024 bits of input");
 
 static void drop_current_rng(void);
 static int hwrng_init(struct hwrng *rng);
-static void hwrng_manage_rngd(void);
+static void hwrng_manage_rngd(struct hwrng *rng);
 
 static inline int rng_get_data(struct hwrng *rng, u8 *buffer, size_t size,
                               int wait);
@@ -160,11 +160,13 @@ static int hwrng_init(struct hwrng *rng)
        reinit_completion(&rng->cleanup_done);
 
 skip_init:
-       current_quality = rng->quality ? : default_quality;
-       if (current_quality > 1024)
-               current_quality = 1024;
+       if (!rng->quality)
+               rng->quality = default_quality;
+       if (rng->quality > 1024)
+               rng->quality = 1024;
+       current_quality = rng->quality; /* obsolete */
 
-       hwrng_manage_rngd();
+       hwrng_manage_rngd(rng);
 
        return 0;
 }
@@ -429,19 +431,24 @@ static int hwrng_fillfn(void *unused)
        long rc;
 
        while (!kthread_should_stop()) {
+               unsigned short quality;
                struct hwrng *rng;
 
-               if (!current_quality)
-                       break;
-
                rng = get_current_rng();
                if (IS_ERR(rng) || !rng)
                        break;
                mutex_lock(&reading_mutex);
                rc = rng_get_data(rng, rng_fillbuf,
                                  rng_buffer_size(), 1);
+               if (current_quality != rng->quality)
+                       rng->quality = current_quality; /* obsolete */
+               quality = rng->quality;
                mutex_unlock(&reading_mutex);
                put_rng(rng);
+
+               if (!quality)
+                       break;
+
                if (rc <= 0) {
                        pr_warn("hwrng: no data available\n");
                        msleep_interruptible(10000);
@@ -451,7 +458,7 @@ static int hwrng_fillfn(void *unused)
                /* If we cannot credit at least one bit of entropy,
                 * keep track of the remainder for the next iteration
                 */
-               entropy = rc * current_quality * 8 + entropy_credit;
+               entropy = rc * quality * 8 + entropy_credit;
                if ((entropy >> 10) == 0)
                        entropy_credit = entropy;
 
@@ -463,14 +470,14 @@ static int hwrng_fillfn(void *unused)
        return 0;
 }
 
-static void hwrng_manage_rngd(void)
+static void hwrng_manage_rngd(struct hwrng *rng)
 {
        if (WARN_ON(!mutex_is_locked(&rng_mutex)))
                return;
 
-       if (current_quality == 0 && hwrng_fill)
+       if (rng->quality == 0 && hwrng_fill)
                kthread_stop(hwrng_fill);
-       if (current_quality > 0 && !hwrng_fill) {
+       if (rng->quality > 0 && !hwrng_fill) {
                hwrng_fill = kthread_run(hwrng_fillfn, NULL, "hwrng");
                if (IS_ERR(hwrng_fill)) {
                        pr_err("hwrng_fill thread creation failed\n");