Subject: [merged] random-fix-accounting-race-condition-with-lockless-irq-entropy_count-update.patch removed from -mm tree
To: jkosina@xxxxxxx,greg@xxxxxxxxx,stable@xxxxxxxxxxxxxxx,tytso@xxxxxxx,mm-commits@xxxxxxxxxxxxxxx
From: akpm@xxxxxxxxxxxxxxxxxxxx
Date: Tue, 28 May 2013 12:37:19 -0700
The patch titled
Subject: random: fix accounting race condition with lockless irq entropy_count update
has been removed from the -mm tree. Its filename was
random-fix-accounting-race-condition-with-lockless-irq-entropy_count-update.patch
This patch was dropped because it was merged into mainline or a subsystem tree
------------------------------------------------------
From: Jiri Kosina <jkosina@xxxxxxx>
Subject: random: fix accounting race condition with lockless irq entropy_count update
Commit 902c098a3663 ("random: use lockless techniques in the interrupt
path") turned IRQ path from being spinlock protected into lockless
cmpxchg-retry update.
That commit removed r->lock serialization between crediting entropy bits
from IRQ context and accounting when extracting entropy on userspace read
path, but didn't turn the r->entropy_count reads/updates in account() to
use cmpxchg as well.
It has been observed, that under certain circumstances this leads to
read() on /dev/urandom to return 0 (EOF), as r->entropy_count gets
corrupted and becomes negative, which in turn results in propagating 0 all
the way from account() to the actual read() call.
Convert the accounting code to be the proper lockless counterpart of what
has been partially done by 902c098a3663.
Signed-off-by: Jiri Kosina <jkosina@xxxxxxx>
Cc: Theodore Ts'o <tytso@xxxxxxx>
Cc: Greg KH <greg@xxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
drivers/char/random.c | 22 +++++++++++++++-------
1 file changed, 15 insertions(+), 7 deletions(-)
diff -puN drivers/char/random.c~random-fix-accounting-race-condition-with-lockless-irq-entropy_count-update drivers/char/random.c
--- a/drivers/char/random.c~random-fix-accounting-race-condition-with-lockless-irq-entropy_count-update
+++ a/drivers/char/random.c
@@ -865,16 +865,24 @@ static size_t account(struct entropy_sto
if (r->entropy_count / 8 < min + reserved) {
nbytes = 0;
} else {
+ int entropy_count, orig;
+retry:
+ entropy_count = orig = ACCESS_ONCE(r->entropy_count);
/* If limited, never pull more than available */
- if (r->limit && nbytes + reserved >= r->entropy_count / 8)
- nbytes = r->entropy_count/8 - reserved;
+ if (r->limit && nbytes + reserved >= entropy_count / 8)
+ nbytes = entropy_count/8 - reserved;
- if (r->entropy_count / 8 >= nbytes + reserved)
- r->entropy_count -= nbytes*8;
- else
- r->entropy_count = reserved;
+ if (entropy_count / 8 >= nbytes + reserved) {
+ entropy_count -= nbytes*8;
+ if (cmpxchg(&r->entropy_count, orig, entropy_count) != orig)
+ goto retry;
+ } else {
+ entropy_count = reserved;
+ if (cmpxchg(&r->entropy_count, orig, entropy_count) != orig)
+ goto retry;
+ }
- if (r->entropy_count < random_write_wakeup_thresh)
+ if (entropy_count < random_write_wakeup_thresh)
wakeup_write = 1;
}
_
Patches currently in -mm which might be from jkosina@xxxxxxx are
linux-next.patch
lib-bitmapc-speed-up-bitmap_find_free_region.patch
lib-bitmapc-speed-up-bitmap_find_free_region-fix.patch
rtc-rtc-hid-sensor-time-allow-full-years-16bit-in-hid-reports.patch
rtc-rtc-hid-sensor-time-allow-16-and-32-bit-values-for-all-attributes.patch
rtc-rtc-hid-sensor-time-add-option-hctosys-to-set-time-at-boot.patch
rtc-rtc-hid-sensor-time-add-support-for-milliseconds.patch
mwave-fix-info-leak-in-mwave_ioctl.patch
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