Tasklets have an inherent problem with memory corruption. The function tasklet_action_common calls tasklet_trylock, then it calls the tasklet callback and then it calls tasklet_unlock. If the tasklet callback frees the structure that contains the tasklet or if it calls some code that may free it, tasklet_unlock will write into free memory. The commits 8e14f610159d and d9a02e016aaf try to fix it for dm-crypt, but it is not a sufficient fix and the data corruption can still happen [1]. There is no fix for dm-verity and dm-verity will write into free memory with every tasklet-processed bio. There will be atomic workqueues implemented in the kernel 6.9 [2]. They will have better interface and they will not suffer from the memory corruption problem. But we need something that stops the memory corruption now and that can be backported to the stable kernels. So, I'm proposing this commit that disables tasklets in both dm-crypt and dm-verity. This commit doesn't remove the tasklet support, because the tasklet code will be reused when atomic workqueues will be implemented. [1] https://lore.kernel.org/all/d390d7ee-f142-44d3-822a-87949e14608b@xxxxxxx/T/ [2] https://lore.kernel.org/lkml/20240130091300.2968534-1-tj@xxxxxxxxxx/ Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx> Cc: stable@xxxxxxxxxxxxxxx Fixes: 39d42fa96ba1b ("dm crypt: add flags to optionally bypass kcryptd workqueues") Fixes: 5721d4e5a9cdb ("dm verity: Add optional "try_verify_in_tasklet" feature") --- drivers/md/dm-crypt.c | 38 ++------------------------------------ drivers/md/dm-verity-target.c | 26 ++------------------------ 2 files changed, 4 insertions(+), 60 deletions(-) Index: linux-2.6/drivers/md/dm-crypt.c =================================================================== --- linux-2.6.orig/drivers/md/dm-crypt.c 2024-01-31 18:58:46.000000000 +0100 +++ linux-2.6/drivers/md/dm-crypt.c 2024-01-31 19:00:05.000000000 +0100 @@ -73,10 +73,8 @@ struct dm_crypt_io { struct bio *base_bio; u8 *integrity_metadata; bool integrity_metadata_from_pool:1; - bool in_tasklet:1; struct work_struct work; - struct tasklet_struct tasklet; struct convert_context ctx; @@ -1762,7 +1760,6 @@ static void crypt_io_init(struct dm_cryp io->ctx.r.req = NULL; io->integrity_metadata = NULL; io->integrity_metadata_from_pool = false; - io->in_tasklet = false; atomic_set(&io->io_pending, 0); } @@ -1771,13 +1768,6 @@ static void crypt_inc_pending(struct dm_ atomic_inc(&io->io_pending); } -static void kcryptd_io_bio_endio(struct work_struct *work) -{ - struct dm_crypt_io *io = container_of(work, struct dm_crypt_io, work); - - bio_endio(io->base_bio); -} - /* * One of the bios was finished. Check for completion of * the whole request and correctly clean up the buffer. @@ -1801,20 +1791,6 @@ static void crypt_dec_pending(struct dm_ base_bio->bi_status = error; - /* - * If we are running this function from our tasklet, - * we can't call bio_endio() here, because it will call - * clone_endio() from dm.c, which in turn will - * free the current struct dm_crypt_io structure with - * our tasklet. In this case we need to delay bio_endio() - * execution to after the tasklet is done and dequeued. - */ - if (io->in_tasklet) { - INIT_WORK(&io->work, kcryptd_io_bio_endio); - queue_work(cc->io_queue, &io->work); - return; - } - bio_endio(base_bio); } @@ -2246,11 +2222,6 @@ static void kcryptd_crypt(struct work_st kcryptd_crypt_write_convert(io); } -static void kcryptd_crypt_tasklet(unsigned long work) -{ - kcryptd_crypt((struct work_struct *)work); -} - static void kcryptd_queue_crypt(struct dm_crypt_io *io) { struct crypt_config *cc = io->cc; @@ -2262,15 +2233,10 @@ static void kcryptd_queue_crypt(struct d * irqs_disabled(): the kernel may run some IO completion from the idle thread, but * it is being executed with irqs disabled. */ - if (in_hardirq() || irqs_disabled()) { - io->in_tasklet = true; - tasklet_init(&io->tasklet, kcryptd_crypt_tasklet, (unsigned long)&io->work); - tasklet_schedule(&io->tasklet); + if (!(in_hardirq() || irqs_disabled())) { + kcryptd_crypt(&io->work); return; } - - kcryptd_crypt(&io->work); - return; } INIT_WORK(&io->work, kcryptd_crypt); Index: linux-2.6/drivers/md/dm-verity-target.c =================================================================== --- linux-2.6.orig/drivers/md/dm-verity-target.c 2024-01-31 18:58:46.000000000 +0100 +++ linux-2.6/drivers/md/dm-verity-target.c 2024-01-31 19:03:14.000000000 +0100 @@ -645,23 +645,6 @@ static void verity_work(struct work_stru verity_finish_io(io, errno_to_blk_status(verity_verify_io(io))); } -static void verity_tasklet(unsigned long data) -{ - struct dm_verity_io *io = (struct dm_verity_io *)data; - int err; - - io->in_tasklet = true; - err = verity_verify_io(io); - if (err == -EAGAIN || err == -ENOMEM) { - /* fallback to retrying with work-queue */ - INIT_WORK(&io->work, verity_work); - queue_work(io->v->verify_wq, &io->work); - return; - } - - verity_finish_io(io, errno_to_blk_status(err)); -} - static void verity_end_io(struct bio *bio) { struct dm_verity_io *io = bio->bi_private; @@ -674,13 +657,8 @@ static void verity_end_io(struct bio *bi return; } - if (static_branch_unlikely(&use_tasklet_enabled) && io->v->use_tasklet) { - tasklet_init(&io->tasklet, verity_tasklet, (unsigned long)io); - tasklet_schedule(&io->tasklet); - } else { - INIT_WORK(&io->work, verity_work); - queue_work(io->v->verify_wq, &io->work); - } + INIT_WORK(&io->work, verity_work); + queue_work(io->v->verify_wq, &io->work); } /*
