loop: Check for overflow while configuring loop

Overview

In the Linux kernel, the following vulnerability has been resolved:

loop: Check for overflow while configuring loop

The userspace can configure a loop using an ioctl call, wherein a configuration of type loop_config is passed (see lo_ioctl()'s case on line 1550 of drivers/block/loop.c). This proceeds to call loop_configure() which in turn calls loop_set_status_from_info() (see line 1050 of loop.c), passing &config->info which is of type loop_info64*. This function then sets the appropriate values, like the offset.

loop_device has lo_offset of type loff_t (see line 52 of loop.c), which is typdef-chained to long long, whereas loop_info64 has lo_offset of type __u64 (see line 56 of include/uapi/linux/loop.h).

The function directly copies offset from info to the device as follows (See line 980 of loop.c): lo->lo_offset = info->lo_offset;

This results in an overflow, which triggers a warning in iomap_iter() due to a call to iomap_iter_done() which has: WARN_ON_ONCE(iter->iomap.offset > iter->pos);

Thus, check for negative value during loop_set_status_from_info().

Bug report: https://syzkaller.appspot.com/bug?id=c620fe14aac810396d3c3edc9ad73848bf69a29e

Affected

• Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 18e28817cb516b39de6281f6db9b0618b2cc7b42
• Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < adf0112d9b8acb03485624220b4934f69bf13369
• Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < a217715338fd48f72114725aa7a40e484a781ca7
• Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < b40877b8562c5720d0a7fce20729f56b75a3dede
• Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 6858933131d0dadac071c4d33335a9ea4b8e76cf
• Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 0455bef69028c65065f16bb04635591b2374249b
• Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 9be7fa7ead18a48940df7b59d993bbc8b9055c15
• Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < c490a0b5a4f36da3918181a8acdc6991d967c5f3
• Linux 2.6.12

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.