tun_build_skb drivers/net/tun.c:1624 [inline] tun_get_user+0xbbd/0x27c0 drivers/net/tun.c:1770 tun_chr_write_iter+0x15e/0x210 drivers/net/tun.c:1999 ================================================================== BUG: KCSAN: data-race in data_push_tail / vsnprintf write to 0xffffffff8939f13f of 32 bytes by task 17499 on cpu 1: vsnprintf+0x2ce/0x860 lib/vsprintf.c:2899 vscnprintf+0x41/0x90 lib/vsprintf.c:3013 printk_sprint+0x30/0x2e0 kernel/printk/printk.c:2222 vprintk_store+0x57b/0x910 kernel/printk/printk.c:2364 vprintk_emit+0x1a4/0x600 kernel/printk/printk.c:2455 vprintk_default+0x26/0x30 kernel/printk/printk.c:2494 vprintk+0x1d/0x30 kernel/printk/printk_safe.c:82 _printk+0x79/0xa0 kernel/printk/printk.c:2504 set_capacity_and_notify+0x1dd/0x230 block/genhd.c:93 loop_set_size+0x2e/0x70 drivers/block/loop.c:220 loop_configure+0x828/0x9c0 drivers/block/loop.c:1079 lo_ioctl+0x1e1/0x13a0 drivers/block/loop.c:1534 blkdev_ioctl+0x387/0x460 block/ioctl.c:804 vfs_ioctl fs/ioctl.c:51 [inline] __do_sys_ioctl fs/ioctl.c:597 [inline] __se_sys_ioctl+0xce/0x140 fs/ioctl.c:583 __x64_sys_ioctl+0x43/0x50 fs/ioctl.c:583 x64_sys_call+0x1563/0x3020 arch/x86/include/generated/asm/syscalls_64.h:17 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0x12c/0x370 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f read to 0xffffffff8939f158 of 8 bytes by task 17503 on cpu 0: data_make_reusable kernel/printk/printk_ringbuffer.c:608 [inline] data_push_tail+0x100/0x470 kernel/printk/printk_ringbuffer.c:693 data_alloc+0x11b/0x390 kernel/printk/printk_ringbuffer.c:1089 prb_reserve+0x8d7/0xae0 kernel/printk/printk_ringbuffer.c:1724 vprintk_store+0x54a/0x910 kernel/printk/printk.c:2354 vprintk_emit+0x1a4/0x600 kernel/printk/printk.c:2455 vprintk_default+0x26/0x30 kernel/printk/printk.c:2494 vprintk+0x1d/0x30 kernel/printk/printk_safe.c:82 _printk+0x79/0xa0 kernel/printk/printk.c:2504 printk_stack_address arch/x86/kernel/dumpstack.c:70 [inline] __show_trace_log_lvl+0x460/0x560 arch/x86/kernel/dumpstack.c:282 __dump_stack+0x1d/0x30 lib/dump_stack.c:94 dump_stack_lvl+0x95/0xd0 lib/dump_stack.c:120 dump_stack+0x15/0x1b lib/dump_stack.c:129 fail_dump lib/fault-inject.c:73 [inline] should_fail_ex+0x263/0x280 lib/fault-inject.c:174 should_fail+0xb/0x20 lib/fault-inject.c:184 should_fail_usercopy+0x1a/0x20 lib/fault-inject-usercopy.c:35 copy_from_user_iter lib/iov_iter.c:50 [inline] iterate_ubuf include/linux/iov_iter.h:30 [inline] iterate_and_advance2 include/linux/iov_iter.h:302 [inline] iterate_and_advance include/linux/iov_iter.h:330 [inline] __copy_from_iter lib/iov_iter.c:261 [inline] _copy_from_iter+0xcf/0xea0 lib/iov_iter.c:272 copy_page_from_iter+0x178/0x2a0 lib/iov_iter.c:434 tun_build_skb drivers/net/tun.c:1624 [inline] tun_get_user+0xbbd/0x27c0 drivers/net/tun.c:1770 tun_chr_write_iter+0x15e/0x210 drivers/net/tun.c:1999 new_sync_write fs/read_write.c:595 [inline] vfs_write+0x5a6/0x9f0 fs/read_write.c:688 ksys_write+0xdc/0x1a0 fs/read_write.c:740 __do_sys_write fs/read_write.c:751 [inline] __se_sys_write fs/read_write.c:748 [inline] __x64_sys_write+0x40/0x50 fs/read_write.c:748 x64_sys_call+0x27e1/0x3020 arch/x86/include/generated/asm/syscalls_64.h:2 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0x12c/0x370 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f value changed: 0x00000000fffff0d1 -> 0x742030206d6f7266 Reported by Kernel Concurrency Sanitizer on: CPU: 0 UID: 0 PID: 17503 Comm: syz.4.3433 Tainted: G W syzkaller #0 PREEMPT(full) Tainted: [W]=WARN Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026 ================================================================== new_sync_write fs/read_write.c:595 [inline] vfs_write+0x5a6/0x9f0 fs/read_write.c:688 ksys_write+0xdc/0x1a0 fs/read_write.c:740 __do_sys_write fs/read_write.c:751 [inline] __se_sys_write fs/read_write.c:748 [inline] __x64_sys_write+0x40/0x50 fs/read_write.c:748 x64_sys_call+0x27e1/0x3020 arch/x86/include/generated/asm/syscalls_64.h:2 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0x12c/0x370 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f RIP: 0033:0x7fc2ac6bcfce Code: 08 0f 85 a5 a8 ff ff 49 89 fb 48 89 f0 48 89 d7 48 89 ce 4c 89 c2 4d 89 ca 4c 8b 44 24 08 4c 8b 4c 24 10 4c 89 5c 24 08 0f 05 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 80 00 00 00 00 48 83 ec 08 RSP: 002b:00007fc2ab156fb8 EFLAGS: 00000246 ORIG_RAX: 0000000000000001 RAX: ffffffffffffffda RBX: 00007fc2ab1576c0 RCX: 00007fc2ac6bcfce RDX: 000000000000004e RSI: 0000200000000480 RDI: 00000000000000c8 RBP: 00007fc2ab157090 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000001 R13: 00007fc2ac976038 R14: 00007fc2ac975fa0 R15: 00007ffed9a37b38