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Wed, 24 Jun 2026 00:18:34 -0700 (PDT) Received: from localhost ([111.228.63.84]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2c7436af585sm131154135ad.5.2026.06.24.00.18.28 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 24 Jun 2026 00:18:33 -0700 (PDT) From: Cen Zhang To: Jens Axboe , Keith Busch , Johannes Thumshirn , Chaitanya Kulkarni , Damien Le Moal , Genjian Zhang , Hans Holmberg , Nilay Shroff , Kees Cook , Matthew Wilcox , Christophe JAILLET , Kyungchan Koh , Shaohua Li Cc: linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, baijiaju1990@gmail.com, zzzccc427@gmail.com Subject: [PATCH] null_blk: cancel bw_timer on add-device error unwind Date: Wed, 24 Jun 2026 15:18:25 +0800 Message-Id: <20260624071825.357098-1-zzzccc427@gmail.com> X-Mailer: git-send-email 2.34.1 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit null_blk starts the bandwidth hrtimer before the later add_disk/device_add failure points. If setup fails after the timer is queued, the shared error unwind frees struct nullb without draining bw_timer, so the callback can run on freed owner state. The buggy scenario involves two paths, with each column showing the order within that path: null_add_dev() error unwind: nullb_bwtimer_fn() callback path: 1. Start bw_timer for a throttled 1. The hrtimer expires after the free. device. 2. nullb_bwtimer_fn() recovers the 2. Hit a later add_disk/device_add embedded owner. failure. 3. The callback reads nullb->dev and 3. Free struct nullb. nullb->q. 4. Release the remaining queue and 4. The stale owner storage is used disk resources. after free. Cancel bw_timer in the shared error unwind before put_disk() and the remaining frees. The normal delete path already uses the same hrtimer_cancel() drain. Validation reproduced this kernel report: BUG: KASAN: slab-use-after-free in nullb_bwtimer_fn+0x13f/0x170 [null_blk] Call Trace: dump_stack_lvl+0x66/0xa0 print_report+0xce/0x630 ? nullb_bwtimer_fn+0x13f/0x170 [null_blk] ? srso_alias_return_thunk+0x5/0xfbef5 ? __virt_addr_valid+0x20d/0x410 ? nullb_bwtimer_fn+0x13f/0x170 [null_blk] kasan_report+0xe0/0x110 ? nullb_bwtimer_fn+0x13f/0x170 [null_blk] ? __pfx_nullb_bwtimer_fn+0x10/0x10 [null_blk] nullb_bwtimer_fn+0x13f/0x170 [null_blk] __hrtimer_run_queues+0x172/0x810 hrtimer_interrupt+0x377/0x7f0 __sysvec_apic_timer_interrupt+0xc3/0x390 sysvec_apic_timer_interrupt+0x67/0x80 asm_sysvec_apic_timer_interrupt+0x1a/0x20 Allocated by task 529: kasan_save_stack+0x33/0x60 kasan_save_track+0x14/0x30 __kasan_kmalloc+0xaa/0xb0 null_add_dev+0x4f9/0x1d10 [null_blk] nullb_device_power_store+0x25f/0x320 [null_blk] configfs_write_iter+0x2be/0x4a0 vfs_write+0x604/0x11f0 ksys_write+0xf9/0x1d0 do_syscall_64+0x115/0x6a0 entry_SYSCALL_64_after_hwframe+0x77/0x7f Freed by task 529: kasan_save_stack+0x33/0x60 kasan_save_track+0x14/0x30 kasan_save_free_info+0x3b/0x60 __kasan_slab_free+0x5f/0x80 kfree+0x307/0x580 null_add_dev+0x1272/0x1d10 [null_blk] nullb_device_power_store+0x25f/0x320 [null_blk] configfs_write_iter+0x2be/0x4a0 vfs_write+0x604/0x11f0 ksys_write+0xf9/0x1d0 do_syscall_64+0x115/0x6a0 entry_SYSCALL_64_after_hwframe+0x77/0x7f Fixes: eff2c4f10873 ("nullb: bandwidth control") Assisted-by: Codex:gpt-5.5 Signed-off-by: Cen Zhang --- drivers/block/null_blk/main.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/drivers/block/null_blk/main.c b/drivers/block/null_blk/main.c index f8c0fd57e041..8f1ad76710a0 100644 --- a/drivers/block/null_blk/main.c +++ b/drivers/block/null_blk/main.c @@ -2062,6 +2062,8 @@ static int null_add_dev(struct nullb_device *dev) out_ida_free: ida_free(&nullb_indexes, nullb->index); out_cleanup_disk: + if (test_bit(NULLB_DEV_FL_THROTTLED, &dev->flags)) + hrtimer_cancel(&nullb->bw_timer); put_disk(nullb->disk); out_cleanup_zone: null_free_zoned_dev(dev); -- 2.43.0