random: silence compiler warnings and fix race

BugLink: http://bugs.launchpad.net/bugs/1701269
commit 4a072c71f49b0a0e495ea13423bdb850da73c58c upstream.

Odd versions of gcc for the sh4 architecture will actually warn about
flags being used while uninitialized, so we set them to zero. Non crazy
gccs will optimize that out again, so it doesn't make a difference.

Next, over aggressive gccs could inline the expression that defines
use_lock, which could then introduce a race resulting in a lock
imbalance. By using READ_ONCE, we prevent that fate. Finally, we make
that assignment const, so that gcc can still optimize a nice amount.

Finally, we fix a potential deadlock between primary_crng.lock and
batched_entropy_reset_lock, where they could be called in opposite
order. Moving the call to invalidate_batched_entropy to outside the lock
rectifies this issue.

Fixes: b169c13de473a85b3c859bb36216a4cb5f00a54a
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Seth Forshee <seth.forshee@canonical.com>

diff --git a/drivers/char/random.c b/drivers/char/random.c
index 2291e6224ed35f3006a08ed19384991b5822e98c..8944a844ca951545ee1bd7566aad36083060cb50 100644 (file)
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -803,13 +803,13 @@ static int crng_fast_load(const char *cp, size_t len)
                p[crng_init_cnt % CHACHA20_KEY_SIZE] ^= *cp;
                cp++; crng_init_cnt++; len--;
        }
+       spin_unlock_irqrestore(&primary_crng.lock, flags);
        if (crng_init_cnt >= CRNG_INIT_CNT_THRESH) {
                invalidate_batched_entropy();
                crng_init = 1;
                wake_up_interruptible(&crng_init_wait);
                pr_notice("random: fast init done\n");
        }
-       spin_unlock_irqrestore(&primary_crng.lock, flags);
        return 1;
 }
 
@@ -841,6 +841,7 @@ static void crng_reseed(struct crng_state *crng, struct entropy_store *r)
        }
        memzero_explicit(&buf, sizeof(buf));
        crng->init_time = jiffies;
+       spin_unlock_irqrestore(&primary_crng.lock, flags);
        if (crng == &primary_crng && crng_init < 2) {
                invalidate_batched_entropy();
                crng_init = 2;
@@ -848,7 +849,6 @@ static void crng_reseed(struct crng_state *crng, struct entropy_store *r)
                wake_up_interruptible(&crng_init_wait);
                pr_notice("random: crng init done\n");
        }
-       spin_unlock_irqrestore(&primary_crng.lock, flags);
 }
 
 static inline void crng_wait_ready(void)
@@ -2037,8 +2037,8 @@ static DEFINE_PER_CPU(struct batched_entropy, batched_entropy_u64);
 u64 get_random_u64(void)
 {
        u64 ret;
-       bool use_lock = crng_init < 2;
-       unsigned long flags;
+       bool use_lock = READ_ONCE(crng_init) < 2;
+       unsigned long flags = 0;
        struct batched_entropy *batch;
 
 #if BITS_PER_LONG == 64
@@ -2069,8 +2069,8 @@ static DEFINE_PER_CPU(struct batched_entropy, batched_entropy_u32);
 u32 get_random_u32(void)
 {
        u32 ret;
-       bool use_lock = crng_init < 2;
-       unsigned long flags;
+       bool use_lock = READ_ONCE(crng_init) < 2;
+       unsigned long flags = 0;
        struct batched_entropy *batch;
 
        if (arch_get_random_int(&ret))