Date:   Fri, 21 Apr 2023 16:52:13 +0200
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     syzbot <syzbot+726dc8c62c3536431ceb@...kaller.appspotmail.com>
Cc:     davem@...emloft.net, herbert@...dor.apana.org.au,
        linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org,
        olivia@...enic.com, syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [crypto?] KCSAN: data-race in random_recv_done /
 virtio_read (3)

On Fri, 21 Apr 2023 at 16:36, syzbot
<syzbot+726dc8c62c3536431ceb@...kaller.appspotmail.com> wrote:
>
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit:    2faac9a98f01 Merge tag 'keys-fixes-20230321' of git://git...
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=1113f21cc80000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=3eb0bb0ae89a5345
> dashboard link: https://syzkaller.appspot.com/bug?extid=726dc8c62c3536431ceb
> 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/571c9c5a3db2/disk-2faac9a9.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/a051e3d7c495/vmlinux-2faac9a9.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/ff5ec0d6e37d/bzImage-2faac9a9.xz
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+726dc8c62c3536431ceb@...kaller.appspotmail.com

Here this:

size = min_t(unsigned int, size, vi->data_avail);
memcpy(buf, vi->data + vi->data_idx, size);
vi->data_idx += size;
vi->data_avail -= size;

runs concurrently with:

if (!virtqueue_get_buf(vi->vq, &vi->data_avail))
    return;
vi->data_idx = 0;

I did not fully grasp how/where vi->data is populated, but it looks
like it can lead to use of uninit/stale random data, or even to out of
bounds access, say if vi->data_avail is already updated, but
vi->data_idx is not yet reset to 0. Then concurrent reading will read
not where it's supposed to read.



> ==================================================================
> BUG: KCSAN: data-race in random_recv_done / virtio_read
>
> read to 0xffff8881019054ec of 4 bytes by task 14079 on cpu 0:
>  copy_data drivers/char/hw_random/virtio-rng.c:70 [inline]
>  virtio_read+0xc3/0x3f0 drivers/char/hw_random/virtio-rng.c:92
>  rng_get_data drivers/char/hw_random/core.c:197 [inline]
>  rng_dev_read+0x1a7/0x5e0 drivers/char/hw_random/core.c:234
>  vfs_read+0x192/0x560 fs/read_write.c:468
>  ksys_read+0xeb/0x1a0 fs/read_write.c:613
>  __do_sys_read fs/read_write.c:623 [inline]
>  __se_sys_read fs/read_write.c:621 [inline]
>  __x64_sys_read+0x42/0x50 fs/read_write.c:621
>  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
>
> write to 0xffff8881019054ec of 4 bytes by interrupt on cpu 1:
>  random_recv_done+0x62/0x90 drivers/char/hw_random/virtio-rng.c:45
>  vring_interrupt+0x150/0x170 drivers/virtio/virtio_ring.c:2491
>  __handle_irq_event_percpu+0x91/0x490 kernel/irq/handle.c:158
>  handle_irq_event_percpu kernel/irq/handle.c:193 [inline]
>  handle_irq_event+0x64/0xf0 kernel/irq/handle.c:210
>  handle_edge_irq+0x17f/0x5a0 kernel/irq/chip.c:819
>  generic_handle_irq_desc include/linux/irqdesc.h:158 [inline]
>  handle_irq arch/x86/kernel/irq.c:231 [inline]
>  __common_interrupt+0x64/0x100 arch/x86/kernel/irq.c:250
>  common_interrupt+0x49/0xc0 arch/x86/kernel/irq.c:240
>  asm_common_interrupt+0x26/0x40 arch/x86/include/asm/idtentry.h:636
>
> value changed: 0x00000000 -> 0x00000040
>
> Reported by Kernel Concurrency Sanitizer on:
> CPU: 1 PID: 14077 Comm: syz-executor.2 Not tainted 6.3.0-rc3-syzkaller-00016-g2faac9a98f01 #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/02/2023
> ==================================================================
> ==================================================================
> BUG: KCSAN: data-race in detach_buf_split / virtqueue_add
>
> read to 0xffff888101a76950 of 4 bytes by task 14131 on cpu 0:
>  virtqueue_add_split drivers/virtio/virtio_ring.c:553 [inline]
>  virtqueue_add+0x4b9/0x2130 drivers/virtio/virtio_ring.c:2117
>  virtqueue_add_inbuf+0x53/0x80 drivers/virtio/virtio_ring.c:2196
>  request_entropy drivers/char/hw_random/virtio-rng.c:61 [inline]
>  copy_data drivers/char/hw_random/virtio-rng.c:74 [inline]
>  virtio_read+0x1c5/0x3f0 drivers/char/hw_random/virtio-rng.c:92
>  rng_get_data drivers/char/hw_random/core.c:197 [inline]
>  rng_dev_read+0x1a7/0x5e0 drivers/char/hw_random/core.c:234
>  vfs_read+0x192/0x560 fs/read_write.c:468
>  ksys_read+0xeb/0x1a0 fs/read_write.c:613
>  __do_sys_read fs/read_write.c:623 [inline]
>  __se_sys_read fs/read_write.c:621 [inline]
>  __x64_sys_read+0x42/0x50 fs/read_write.c:621
>  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-write to 0xffff888101a76950 of 4 bytes by interrupt on cpu 1:
>  detach_buf_split+0x2fc/0x570 drivers/virtio/virtio_ring.c:757
>  virtqueue_get_buf_ctx_split drivers/virtio/virtio_ring.c:835 [inline]
>  virtqueue_get_buf_ctx+0x3c8/0x5c0 drivers/virtio/virtio_ring.c:2311
>  virtqueue_get_buf+0x1f/0x30 drivers/virtio/virtio_ring.c:2317
>  random_recv_done+0x4c/0x90 drivers/char/hw_random/virtio-rng.c:42
>  vring_interrupt+0x150/0x170 drivers/virtio/virtio_ring.c:2491
>  __handle_irq_event_percpu+0x91/0x490 kernel/irq/handle.c:158
>  handle_irq_event_percpu kernel/irq/handle.c:193 [inline]
>  handle_irq_event+0x64/0xf0 kernel/irq/handle.c:210
>  handle_edge_irq+0x17f/0x5a0 kernel/irq/chip.c:819
>  generic_handle_irq_desc include/linux/irqdesc.h:158 [inline]
>  handle_irq arch/x86/kernel/irq.c:231 [inline]
>  __common_interrupt+0x64/0x100 arch/x86/kernel/irq.c:250
>  common_interrupt+0x9e/0xc0 arch/x86/kernel/irq.c:240
>  asm_common_interrupt+0x26/0x40 arch/x86/include/asm/idtentry.h:636
>  xas_find+0x10a/0x3f0
>  find_get_entry mm/filemap.c:2008 [inline]
>  filemap_get_folios+0xa4/0x3f0 mm/filemap.c:2174
>  mpage_map_and_submit_buffers fs/ext4/inode.c:2358 [inline]
>  mpage_map_and_submit_extent fs/ext4/inode.c:2513 [inline]
>  ext4_do_writepages+0x1017/0x2140 fs/ext4/inode.c:2876
>  ext4_writepages+0x127/0x250 fs/ext4/inode.c:2964
>  do_writepages+0x1c5/0x340 mm/page-writeback.c:2551
>  filemap_fdatawrite_wbc+0xdb/0xf0 mm/filemap.c:390
>  __filemap_fdatawrite_range mm/filemap.c:423 [inline]
>  __filemap_fdatawrite mm/filemap.c:429 [inline]
>  filemap_flush+0x95/0xc0 mm/filemap.c:456
>  ext4_alloc_da_blocks+0x50/0x130 fs/ext4/inode.c:3218
>  ext4_release_file+0x5f/0x1c0 fs/ext4/file.c:158
>  __fput+0x245/0x570 fs/file_table.c:321
>  ____fput+0x15/0x20 fs/file_table.c:349
>  task_work_run+0x123/0x160 kernel/task_work.c:179
>  exit_task_work include/linux/task_work.h:38 [inline]
>  do_exit+0x600/0x1710 kernel/exit.c:869
>  do_group_exit+0x101/0x150 kernel/exit.c:1019
>  get_signal+0xea9/0xfe0 kernel/signal.c:2859
>  arch_do_signal_or_restart+0x89/0x2b0 arch/x86/kernel/signal.c:306
>  exit_to_user_mode_loop+0x6d/0xe0 kernel/entry/common.c:168
>  exit_to_user_mode_prepare+0x6a/0xa0 kernel/entry/common.c:203
>  irqentry_exit_to_user_mode+0x9/0x20 kernel/entry/common.c:309
>  irqentry_exit+0x12/0x40 kernel/entry/common.c:412
>  exc_general_protection+0x339/0x4c0 arch/x86/kernel/traps.c:728
>  asm_exc_general_protection+0x26/0x30 arch/x86/include/asm/idtentry.h:564
>
> value changed: 0x00000001 -> 0x00000000
>
> Reported by Kernel Concurrency Sanitizer on:
> CPU: 1 PID: 14098 Comm: syz-executor.1 Not tainted 6.3.0-rc3-syzkaller-00016-g2faac9a98f01 #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/02/2023
> ==================================================================
>
>
> ---
> 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@...glegroups.com.
>
> syzbot will keep track of this issue. See:
> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

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