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

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Date: Sun, 28 Mar 2021 11:47:22 +0800
From: - Nop <nopitydays@...il.com>
To: oss-security@...ts.openwall.com
Subject: Linux Kernel: out of bounds array access in dm-ioctl.c

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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