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authorWeijie Yang <weijie.yang@samsung.com>2014-10-29 14:50:57 -0700
committerAlex Shi <alex.shi@linaro.org>2015-05-11 21:31:01 +0800
commitea56241654a2c7ef9a1122a7ad5c751527ed9b17 (patch)
treebc3b0742b4132b355eedc0b4d76980f83e40c230 /drivers
parentb900447eb093095e133ffacb6a7de29660e09eae (diff)
downloadlinux-linaro-stable-ea56241654a2c7ef9a1122a7ad5c751527ed9b17.tar.gz
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> (cherry picked from commit 5a99e95b8d1cd47f6feddcdca6c71d22060df8a2) Signed-off-by: Alex Shi <alex.shi@linaro.org>
Diffstat (limited to 'drivers')
-rw-r--r--drivers/block/zram/zram_drv.c10
1 files changed, 6 insertions, 4 deletions
diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 3503019a9672..bf9fea268db4 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;