Re: Linux Kernel: out of bounds array access in dm-ioctl.c

[John Haxby <john.haxby () oracle com>]

> On 28 Mar 2021, at 04:47, - Nop <nopitydays () gmail com> wrote:
>
> Hi,
>
> We found an out of bounds array accessing bug in drivers/md/dm-ioctl.c, and
> reproduced it in the latest kernel (v5.11.10).
>
> The root cause of this BUG is :
>
> The field "data_size" in function ctl_ioctl is fully controlled by users
> and this argument controls the size of kvmalloc in function copy_params.
>
> When the data_size is in a range of [0x131,0x138], the allocated memory
> which is pointed by the variable "param" used in ioctl
> "DM_LIST_DEVICES_CMD" is too small, causing an oob bug at line "nl->dev =
> 0; /* Flags no data */" (
> https://github.com/torvalds/linux/blob/0d02ec6b3136c73c09e7859f0d0e4e2c4c07b49b/drivers/md/dm-ioctl.c#L538
> )

DM_LIST_DEVICES_CMD, and in fact, any function called from ctl_ioctl is limited to users with CAP_SYS_ADMIN.  Without 
that root-equivalent privilege I don't see any way to exploit this bug.   Did you find a way to exploit it as an 
unprivileged user?

jch

> Attachments are the poc, kernel config and Kernel report.
>
> The patch:
> https://github.com/torvalds/linux/commit/4edbe1d7bcffcd6269f3b5eb63f710393ff2ec7a
>     * Grab our output buffer.
>     */
>     nl = orig_nl = get_result_buffer(param, param_size, &len);
> -    if (len < needed) {
> +    if (len < needed || len < sizeof(nl->dev)) {
>         param->flags |= DM_BUFFER_FULL_FLAG;
>         goto out;
>     }
>
> Regards,
> Bodong Zhao of NISL lab, Tsinghua University

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