Patch "random: silence compiler warnings and fix race" has been added to the 4.11-stable tree

PATCH [email protected] 1 participant 1 message Jun 26, 2017

Subsystems (2)

Stable branch Random number driver

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2017-06-26 06:43 UTC #0 lore raw

This is a note to let you know that I've just added the patch titled

random: silence compiler warnings and fix race

to the 4.11-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
random-silence-compiler-warnings-and-fix-race.patch
and it can be found in the queue-4.11 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

Quoted 1 line

From 4a072c71f49b0a0e495ea13423bdb850da73c58c Mon Sep 17 00:00:00 2001

From: "Jason A. Donenfeld" <[email protected]>
Date: Thu, 15 Jun 2017 00:45:26 +0200
Subject: random: silence compiler warnings and fix race

From: Jason A. Donenfeld <[email protected]>

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 <[email protected]>

Signed-off-by Theodore Ts'o <[email protected]>

Signed-off-by Greg Kroah-Hartman <[email protected]>

---
 drivers/char/random.c |   12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

drivers/char/random.c +6 -6

@@ -803,13 +803,13 @@ static int crng_fast_load(const char *cp
 		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_stat
 	}
 	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_stat
 		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_ent
 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_ent
 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))

Patches currently in stable-queue which might be from [email protected] are

queue-4.11/random-silence-compiler-warnings-and-fix-race.patch