The patch titled
Subject: zram: avoid NULL pointer access in concurrent situation
has been added to the -mm tree. Its filename is
zram-avoid-null-pointer-access-in-concurrent-situation.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/zram-avoid-null-pointer-access-in-concurrent-situation.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/zram-avoid-null-pointer-access-in-concurrent-situation.patch
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From: Weijie Yang <weijie.yang@xxxxxxxxxxx>
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@xxxxxxxxxxx>
Acked-by: Minchan Kim <minchan@xxxxxxxxxx>
Acked-by: Sergey Senozhatsky <sergey.senozhatsky@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
drivers/block/zram/zram_drv.c | 10 ++++++----
1 file changed, 6 insertions(+), 4 deletions(-)
diff -puN drivers/block/zram/zram_drv.c~zram-avoid-null-pointer-access-in-concurrent-situation drivers/block/zram/zram_drv.c
--- a/drivers/block/zram/zram_drv.c~zram-avoid-null-pointer-access-in-concurrent-situation
+++ a/drivers/block/zram/zram_drv.c
@@ -99,11 +99,12 @@ static ssize_t mem_used_total_show(struc
{
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
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;
_
Patches currently in -mm which might be from weijie.yang@xxxxxxxxxxx are
zram-avoid-null-pointer-access-in-concurrent-situation.patch
x86-cma-reserve-dma-contiguous-area-after-initmem_init.patch
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