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SubjectRe: [PATCH -next] nbd: Fix use-after-free in pid_show
On Wed, Oct 20, 2021 at 03:39:59PM +0800, Ye Bin wrote:
> I got issue as follows:
> [ 263.886511] BUG: KASAN: use-after-free in pid_show+0x11f/0x13f
> [ 263.888359] Read of size 4 at addr ffff8880bf0648c0 by task cat/746
> [ 263.890479] CPU: 0 PID: 746 Comm: cat Not tainted 4.19.90-dirty #140
> [ 263.893162] Call Trace:
> [ 263.893509] dump_stack+0x108/0x15f
> [ 263.893999] print_address_description+0xa5/0x372
> [ 263.894641] kasan_report.cold+0x236/0x2a8
> [ 263.895696] __asan_report_load4_noabort+0x25/0x30
> [ 263.896365] pid_show+0x11f/0x13f
> [ 263.897422] dev_attr_show+0x48/0x90
> [ 263.898361] sysfs_kf_seq_show+0x24d/0x4b0
> [ 263.899479] kernfs_seq_show+0x14e/0x1b0
> [ 263.900029] seq_read+0x43f/0x1150
> [ 263.900499] kernfs_fop_read+0xc7/0x5a0
> [ 263.903764] vfs_read+0x113/0x350
> [ 263.904231] ksys_read+0x103/0x270
> [ 263.905230] __x64_sys_read+0x77/0xc0
> [ 263.906284] do_syscall_64+0x106/0x360
> [ 263.906797] entry_SYSCALL_64_after_hwframe+0x44/0xa9
>
> Reproduce this issue as follows:
> 1. nbd-server 8000 /tmp/disk
> 2. nbd-client localhost 8000 /dev/nbd1
> 3. cat /sys/block/nbd1/pid
> Then trigger use-after-free in pid_show.
>
> Reason is after do step '2', nbd-client progress is already exit. So
> it's task_struct already freed.
> To solve this issue, revert part of 6521d39a64b3's modify and remove
> useless 'recv_task' member of nbd_device.
>
> Fixes: 6521d39a64b3 ("nbd: Remove variable 'pid'")
> Signed-off-by: Ye Bin <yebin10@huawei.com>

Reviewed-by: Josef Bacik <josef@toxicpanda.com>

Thanks,

Josef

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