From 5a99e95b8d1cd47f6feddcdca6c71d22060df8a2 Mon Sep 17 00:00:00 2001 From: Weijie Yang 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 Acked-by: Minchan Kim Acked-by: Sergey Senozhatsky Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- drivers/block/zram/zram_drv.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-) (limited to 'drivers/block') diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c index 0e63e8aa8279..2ad0b5bce44b 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 v1.2.1