diff options
| author | Richard Chang <richardycc@google.com> | 2026-05-12 07:49:18 +0000 |
|---|---|---|
| committer | Andrew Morton <akpm@linux-foundation.org> | 2026-05-21 19:06:11 -0700 |
| commit | bf62f69574b19720ae5fbbbcdf24a0c4e3e05e43 (patch) | |
| tree | 598160334ce41b454e0537a6e1a1d10cb5133d23 | |
| parent | 3b041514cb6eae45869b020f743c14d983363222 (diff) | |
zram: fix use-after-free in zram_writeback_endio
A crash was observed in zram_writeback_endio due to a NULL pointer
dereference in wake_up. The root cause is a race condition between the
bio completion handler (zram_writeback_endio) and the writeback task.
In zram_writeback_endio, wake_up() is called on &wb_ctl->done_wait after
releasing wb_ctl->done_lock. This creates a race window where the
writeback task can see num_inflight become 0, return, and free wb_ctl
before zram_writeback_endio calls wake_up().
CPU 0 (zram_writeback_endio) CPU 1 (writeback_store)
============================ ============================
zram_writeback_slots
zram_submit_wb_request
zram_submit_wb_request
wait_event(wb_ctl->done_wait)
spin_lock(&wb_ctl->done_lock);
list_add(&req->entry, &wb_ctl->done_reqs);
spin_unlock(&wb_ctl->done_lock);
wake_up(&wb_ctl->done_wait);
zram_complete_done_reqs
spin_lock(&wb_ctl->done_lock);
list_add(&req->entry, &wb_ctl->done_reqs);
spin_unlock(&wb_ctl->done_lock);
while (num_inflight) > 0)
spin_lock(&wb_ctl->done_lock);
list_del(&req->entry);
spin_unlock(&wb_ctl->done_lock);
// num_inflight becomes 0
atomic_dec(num_inflight);
// Leave zram_writeback_slots
// Free wb_ctl
release_wb_ctl(wb_ctl);
// UAF crash!
wake_up(&wb_ctl->done_wait);
This patch fixes this race by using RCU. By protecting wb_ctl with
rcu_read_lock() in zram_writeback_endio and using kfree_rcu() to free it,
we ensure that wb_ctl remains valid during the execution of
zram_writeback_endio.
Link: https://lore.kernel.org/20260512074918.2606208-1-richardycc@google.com
Fixes: f405066a1f0d ("zram: introduce writeback bio batching")
Signed-off-by: Richard Chang <richardycc@google.com>
Suggested-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Suggested-by: Minchan Kim <minchan@kernel.org>
Acked-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Acked-by: Minchan Kim <minchan@kernel.org>
Cc: Brian Geffon <bgeffon@google.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Martin Liu <liumartin@google.com>
Cc: wang wei <a929244872@163.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
| -rw-r--r-- | drivers/block/zram/zram_drv.c | 6 |
1 files changed, 5 insertions, 1 deletions
diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c index aebc710f0d6a..07111455eecf 100644 --- a/drivers/block/zram/zram_drv.c +++ b/drivers/block/zram/zram_drv.c @@ -33,6 +33,7 @@ #include <linux/cpuhotplug.h> #include <linux/part_stat.h> #include <linux/kernel_read_file.h> +#include <linux/rcupdate.h> #include "zram_drv.h" @@ -504,6 +505,7 @@ struct zram_wb_ctl { wait_queue_head_t done_wait; spinlock_t done_lock; atomic_t num_inflight; + struct rcu_head rcu; }; struct zram_wb_req { @@ -847,7 +849,7 @@ static void release_wb_ctl(struct zram_wb_ctl *wb_ctl) release_wb_req(req); } - kfree(wb_ctl); + kfree_rcu(wb_ctl, rcu); } static struct zram_wb_ctl *init_wb_ctl(struct zram *zram) @@ -964,11 +966,13 @@ static void zram_writeback_endio(struct bio *bio) struct zram_wb_ctl *wb_ctl = bio->bi_private; unsigned long flags; + rcu_read_lock(); spin_lock_irqsave(&wb_ctl->done_lock, flags); list_add(&req->entry, &wb_ctl->done_reqs); spin_unlock_irqrestore(&wb_ctl->done_lock, flags); wake_up(&wb_ctl->done_wait); + rcu_read_unlock(); } static void zram_submit_wb_request(struct zram *zram, |