From 5a99e95b8d1cd47f6feddcdca6c71d22060df8a2 Mon Sep 17 00:00:00 2001
From: Weijie Yang <weijie.yang@samsung.com>
Date: Wed, 29 Oct 2014 14:50:57 -0700
Subject: zram: avoid NULL pointer access in concurrent situation
There is a rare NULL pointer bug in mem_used_total_show() and
mem_used_max_store() in concurrent situation, like this:
zram is not initialized, process A is a mem_used_total reader which runs
periodically, while process B try to init zram.
process A process B
access meta, get a NULL value
init zram, done
init_done() is true
access meta->mem_pool, get a NULL pointer BUG
This patch fixes this issue.
Signed-off-by: Weijie Yang <weijie.yang@samsung.com>
Acked-by: Minchan Kim <minchan@kernel.org>
Acked-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
drivers/block/zram/zram_drv.c | 10 ++++++----
1 file changed, 6 insertions(+), 4 deletions(-)
(limited to 'drivers/block/zram')
diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 0e63e8a..2ad0b5b 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -99,11 +99,12 @@ static ssize_t mem_used_total_show(struct device *dev,
{
u64 val = 0;
struct zram *zram = dev_to_zram(dev);
- struct zram_meta *meta = zram->meta;
down_read(&zram->init_lock);
- if (init_done(zram))
+ if (init_done(zram)) {
+ struct zram_meta *meta = zram->meta;
val = zs_get_total_pages(meta->mem_pool);
+ }
up_read(&zram->init_lock);
return scnprintf(buf, PAGE_SIZE, "%llu\n", val << PAGE_SHIFT);
@@ -173,16 +174,17 @@ static ssize_t mem_used_max_store(struct device *dev,
int err;
unsigned long val;
struct zram *zram = dev_to_zram(dev);
- struct zram_meta *meta = zram->meta;
err = kstrtoul(buf, 10, &val);
if (err || val != 0)
return -EINVAL;
down_read(&zram->init_lock);
- if (init_done(zram))
+ if (init_done(zram)) {
+ struct zram_meta *meta = zram->meta;
atomic_long_set(&zram->stats.max_used_pages,
zs_get_total_pages(meta->mem_pool));
+ }
up_read(&zram->init_lock);
return len;
--
cgit v1.1