From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Date: Tue, 10 Apr 2018 12:56:35 +0000 (+0200)
Subject: 4.9-stable patches
X-Git-Tag: v4.16.2~20
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=88cd34304d58566a2d8957b5b84cadb03ca9ace4;p=thirdparty%2Fkernel%2Fstable-queue.git

4.9-stable patches

added patches:
	random-use-lockless-method-of-accessing-and-updating-f-reg_idx.patch
---

diff --git a/queue-4.9/random-use-lockless-method-of-accessing-and-updating-f-reg_idx.patch b/queue-4.9/random-use-lockless-method-of-accessing-and-updating-f-reg_idx.patch
new file mode 100644
index 00000000000..aa6476220e7
--- /dev/null
+++ b/queue-4.9/random-use-lockless-method-of-accessing-and-updating-f-reg_idx.patch
@@ -0,0 +1,45 @@
+From 92e75428ffc90e2a0321062379f883f3671cfebe Mon Sep 17 00:00:00 2001
+From: Theodore Ts'o <tytso@mit.edu>
+Date: Wed, 7 Jun 2017 19:01:32 -0400
+Subject: random: use lockless method of accessing and updating f->reg_idx
+
+From: Theodore Ts'o <tytso@mit.edu>
+
+commit 92e75428ffc90e2a0321062379f883f3671cfebe upstream.
+
+Linus pointed out that there is a much more efficient way of avoiding
+the problem that we were trying to address in commit 9dfa7bba35ac0:
+"fix race in drivers/char/random.c:get_reg()".
+
+Signed-off-by: Theodore Ts'o <tytso@mit.edu>
+Cc: Michael Schmitz <schmitzmic@gmail.com>
+Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+
+---
+ drivers/char/random.c |   12 ++++++------
+ 1 file changed, 6 insertions(+), 6 deletions(-)
+
+--- a/drivers/char/random.c
++++ b/drivers/char/random.c
+@@ -1115,15 +1115,15 @@ static void add_interrupt_bench(cycles_t
+ static __u32 get_reg(struct fast_pool *f, struct pt_regs *regs)
+ {
+ 	__u32 *ptr = (__u32 *) regs;
+-	unsigned long flags;
++	unsigned int idx;
+ 
+ 	if (regs == NULL)
+ 		return 0;
+-	local_irq_save(flags);
+-	if (f->reg_idx >= sizeof(struct pt_regs) / sizeof(__u32))
+-		f->reg_idx = 0;
+-	ptr += f->reg_idx++;
+-	local_irq_restore(flags);
++	idx = READ_ONCE(f->reg_idx);
++	if (idx >= sizeof(struct pt_regs) / sizeof(__u32))
++		idx = 0;
++	ptr += idx++;
++	WRITE_ONCE(f->reg_idx, idx);
+ 	return *ptr;
+ }
+ 
diff --git a/queue-4.9/series b/queue-4.9/series
index 23229b5ee9e..ed2f2151bec 100644
--- a/queue-4.9/series
+++ b/queue-4.9/series
@@ -274,3 +274,4 @@ ipsec-check-return-value-of-skb_to_sgvec-always.patch
 rxrpc-check-return-value-of-skb_to_sgvec-always.patch
 virtio_net-check-return-value-of-skb_to_sgvec-always.patch
 virtio_net-check-return-value-of-skb_to_sgvec-in-one-more-location.patch
+random-use-lockless-method-of-accessing-and-updating-f-reg_idx.patch