From: Zheng Qixing Date: Thu, 12 Jun 2025 13:24:05 +0000 (+0800) Subject: nbd: fix uaf in nbd_genl_connect() error path X-Git-Tag: block-6.16-20250710~1 X-Git-Url: https://git.kernel.dk/?a=commitdiff_plain;h=aa9552438ebf015fc5f9f890dbfe39f0c53cf37e;p=linux-block.git nbd: fix uaf in nbd_genl_connect() error path There is a use-after-free issue in nbd: block nbd6: Receive control failed (result -104) block nbd6: shutting down sockets ================================================================== BUG: KASAN: slab-use-after-free in recv_work+0x694/0xa80 drivers/block/nbd.c:1022 Write of size 4 at addr ffff8880295de478 by task kworker/u33:0/67 CPU: 2 UID: 0 PID: 67 Comm: kworker/u33:0 Not tainted 6.15.0-rc5-syzkaller-00123-g2c89c1b655c0 #0 PREEMPT(full) Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014 Workqueue: nbd6-recv recv_work Call Trace: __dump_stack lib/dump_stack.c:94 [inline] dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:120 print_address_description mm/kasan/report.c:408 [inline] print_report+0xc3/0x670 mm/kasan/report.c:521 kasan_report+0xe0/0x110 mm/kasan/report.c:634 check_region_inline mm/kasan/generic.c:183 [inline] kasan_check_range+0xef/0x1a0 mm/kasan/generic.c:189 instrument_atomic_read_write include/linux/instrumented.h:96 [inline] atomic_dec include/linux/atomic/atomic-instrumented.h:592 [inline] recv_work+0x694/0xa80 drivers/block/nbd.c:1022 process_one_work+0x9cc/0x1b70 kernel/workqueue.c:3238 process_scheduled_works kernel/workqueue.c:3319 [inline] worker_thread+0x6c8/0xf10 kernel/workqueue.c:3400 kthread+0x3c2/0x780 kernel/kthread.c:464 ret_from_fork+0x45/0x80 arch/x86/kernel/process.c:153 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245 nbd_genl_connect() does not properly stop the device on certain error paths after nbd_start_device() has been called. This causes the error path to put nbd->config while recv_work continue to use the config after putting it, leading to use-after-free in recv_work. This patch moves nbd_start_device() after the backend file creation. Reported-by: syzbot+48240bab47e705c53126@syzkaller.appspotmail.com Closes: https://lore.kernel.org/all/68227a04.050a0220.f2294.00b5.GAE@google.com/T/ Fixes: 6497ef8df568 ("nbd: provide a way for userspace processes to identify device backends") Signed-off-by: Zheng Qixing Reviewed-by: Yu Kuai Link: https://lore.kernel.org/r/20250612132405.364904-1-zhengqixing@huaweicloud.com Signed-off-by: Jens Axboe --- diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c index 7bdc7eb808ea..2592bd19ebc1 100644 --- a/drivers/block/nbd.c +++ b/drivers/block/nbd.c @@ -2198,9 +2198,7 @@ again: goto out; } } - ret = nbd_start_device(nbd); - if (ret) - goto out; + if (info->attrs[NBD_ATTR_BACKEND_IDENTIFIER]) { nbd->backend = nla_strdup(info->attrs[NBD_ATTR_BACKEND_IDENTIFIER], GFP_KERNEL); @@ -2216,6 +2214,8 @@ again: goto out; } set_bit(NBD_RT_HAS_BACKEND_FILE, &config->runtime_flags); + + ret = nbd_start_device(nbd); out: mutex_unlock(&nbd->config_lock); if (!ret) {