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List:       oss-security
Subject:    [oss-security] Re: Linux Kernel: out of bounds array access in dm-ioctl.c
From:       - Nop <nopitydays () gmail ! com>
Date:       2021-04-19 7:19:58
Message-ID: CA+-U7QBGWLJkSvg+7g8K-Aj02Svp9e6HhSRbXYPVBp8gZUBQVA () mail ! gmail ! com
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Hi,

sorry for the late reply.

> 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?

Yes, this IOCTL does need CAP_SYS_ADMIN capability which is very close
to the real root user.

The only possible exploitable scenario that I can imagine is, a user
with CAP_SYS_ADMIN cap in a container attacks the shared kernel to
break through the seccomp limitation.

However, it is quite rare.


Thanks,

Bodong


On Sun, Mar 28, 2021 at 11:47 AM - 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
>  )
> 
> 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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