On Fri, Apr 21, 2023 at 04:43:19PM +0200, Dmitry Vyukov wrote: > On Fri, 21 Apr 2023 at 16:33, syzbot > <syzbot+c2de99a72baaa06d31f3@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote: > > > > Hello, > > > > syzbot found the following issue on: > > > > HEAD commit: 76f598ba7d8e Merge tag 'for-linus' of git://git.kernel.org.. > > git tree: upstream > > console output: https://syzkaller.appspot.com/x/log.txt?x=133bfbedc80000 > > kernel config: https://syzkaller.appspot.com/x/.config?x=9c5d44636e91081b > > dashboard link: https://syzkaller.appspot.com/bug?extid=c2de99a72baaa06d31f3 > > compiler: Debian clang version 15.0.7, GNU ld (GNU Binutils for Debian) 2.35.2 > > > > Unfortunately, I don't have any reproducer for this issue yet. > > > > Downloadable assets: > > disk image: https://storage.googleapis.com/syzbot-assets/a3654f5f77b9/disk-76f598ba.raw.xz > > vmlinux: https://storage.googleapis.com/syzbot-assets/abfb4aaa5772/vmlinux-76f598ba.xz > > kernel image: https://storage.googleapis.com/syzbot-assets/789fb5546551/bzImage-76f598ba.xz > > > > IMPORTANT: if you fix the issue, please add the following tag to the commit: > > Reported-by: syzbot+c2de99a72baaa06d31f3@xxxxxxxxxxxxxxxxxxxxxxxxx > > +bpf maintainers > > If I am reading this correctly, this can cause a leak of kernel memory > and/or crash via bpf_get_current_comm helper. > > strcpy() can temporary leave comm buffer non-0 terminated as it > terminates it only after the copy: > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/lib/string.c?id=76f598ba7d8e2bfb4855b5298caedd5af0c374a8#n184 > > If bpf_get_current_comm() observes such non-0-terminated comm, it will > start reading off bounds. Just to be clear, this isn't ext4 at all; ext4 happens to be calling kthread_create(), but it's actually a generic kthread problem, right? I'm not sure how it is that bpf is able to see the task before comm is initialised; that seems to be the real race here, that comm is not set before the kthread is a schedulable entity? Adding the scheduler people. > > ================================================================== > > BUG: KCSAN: data-race in strscpy / strscpy > > > > write to 0xffff88812ed8b730 of 8 bytes by task 16157 on cpu 1: > > strscpy+0xa9/0x170 lib/string.c:165 > > strscpy_pad+0x27/0x80 lib/string_helpers.c:835 > > __set_task_comm+0x46/0x140 fs/exec.c:1232 > > set_task_comm include/linux/sched.h:1984 [inline] > > __kthread_create_on_node+0x2b2/0x320 kernel/kthread.c:474 > > kthread_create_on_node+0x8a/0xb0 kernel/kthread.c:512 > > ext4_run_lazyinit_thread fs/ext4/super.c:3848 [inline] > > ext4_register_li_request+0x407/0x650 fs/ext4/super.c:3983 > > __ext4_fill_super fs/ext4/super.c:5480 [inline] > > ext4_fill_super+0x3f4a/0x43f0 fs/ext4/super.c:5637 > > get_tree_bdev+0x2b1/0x3a0 fs/super.c:1303 > > ext4_get_tree+0x1c/0x20 fs/ext4/super.c:5668 > > vfs_get_tree+0x51/0x190 fs/super.c:1510 > > do_new_mount+0x200/0x650 fs/namespace.c:3042 > > path_mount+0x498/0xb40 fs/namespace.c:3372 > > do_mount fs/namespace.c:3385 [inline] > > __do_sys_mount fs/namespace.c:3594 [inline] > > __se_sys_mount+0x27f/0x2d0 fs/namespace.c:3571 > > __x64_sys_mount+0x67/0x80 fs/namespace.c:3571 > > do_syscall_x64 arch/x86/entry/common.c:50 [inline] > > do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80 > > entry_SYSCALL_64_after_hwframe+0x63/0xcd > > > > read to 0xffff88812ed8b733 of 1 bytes by task 16161 on cpu 0: > > strscpy+0xde/0x170 lib/string.c:174 > > ____bpf_get_current_comm kernel/bpf/helpers.c:260 [inline] > > bpf_get_current_comm+0x45/0x70 kernel/bpf/helpers.c:252 > > ___bpf_prog_run+0x281/0x3050 kernel/bpf/core.c:1822 > > __bpf_prog_run32+0x74/0xa0 kernel/bpf/core.c:2043 > > bpf_dispatcher_nop_func include/linux/bpf.h:1124 [inline] > > __bpf_prog_run include/linux/filter.h:601 [inline] > > bpf_prog_run include/linux/filter.h:608 [inline] > > __bpf_trace_run kernel/trace/bpf_trace.c:2263 [inline] > > bpf_trace_run4+0x9f/0x140 kernel/trace/bpf_trace.c:2304 > > __traceiter_sched_switch+0x3a/0x50 include/trace/events/sched.h:222 > > trace_sched_switch include/trace/events/sched.h:222 [inline] > > __schedule+0x7e7/0x8e0 kernel/sched/core.c:6622 > > schedule+0x51/0x80 kernel/sched/core.c:6701 > > schedule_preempt_disabled+0x10/0x20 kernel/sched/core.c:6760 > > kthread+0x11c/0x1e0 kernel/kthread.c:369 > > ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:308 > > > > value changed: 0x72 -> 0x34 > > > > Reported by Kernel Concurrency Sanitizer on: > > CPU: 0 PID: 16161 Comm: ext4lazyinit Not tainted 6.3.0-rc5-syzkaller-00022-g76f598ba7d8e #0 > > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/30/2023 > > ================================================================== > > > > > > --- > > This report is generated by a bot. It may contain errors. > > See https://goo.gl/tpsmEJ for more information about syzbot. > > syzbot engineers can be reached at syzkaller@xxxxxxxxxxxxxxxx. > > > > syzbot will keep track of this issue. See: > > https://goo.gl/tpsmEJ#status for how to communicate with syzbot. >
