CVE-2025-38592

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

Bluetooth: hcidevcddump: fix out-of-bounds via dev_coredumpv

Currently both devcoredumpv and skbputdata in hcidevcddump use hdev->dump.head. However, devcoredumpv can free the buffer. From devcoredumpmtimeout documentation, which is used by dev_coredumpv:

> Creates a new device coredump for the given device. If a previous one hasn't
> been read yet, the new coredump is discarded. The data lifetime is determined
> by the device coredump framework and when it is no longer needed the @free
> function will be called to free the data.

If the data has not been read by the userspace yet, devcoredumpv will discard new buffer, freeing hdev->dump.head. This leads to vmalloc-out-of-bounds error when skbput_data tries to access hdev->dump.head.

A crash report from syzbot illustrates this:

==================================================================
BUG: KASAN: vmalloc-out-of-bounds in skb_put_data
include/linux/skbuff.h:2752 [inline]
BUG: KASAN: vmalloc-out-of-bounds in hci_devcd_dump+0x142/0x240
net/bluetooth/coredump.c:258
Read of size 140 at addr ffffc90004ed5000 by task kworker/u9:2/5844

CPU: 1 UID: 0 PID: 5844 Comm: kworker/u9:2 Not tainted
6.14.0-syzkaller-10892-g4e82c87058f4 #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 02/12/2025
Workqueue: hci0 hci_devcd_timeout
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:408 [inline]
 print_report+0xc3/0x670 mm/kasan/report.c:521
 kasan_report+0xe0/0x110 mm/kasan/report.c:634
 check_region_inline mm/kasan/generic.c:183 [inline]
 kasan_check_range+0xef/0x1a0 mm/kasan/generic.c:189
 __asan_memcpy+0x23/0x60 mm/kasan/shadow.c:105
 skb_put_data include/linux/skbuff.h:2752 [inline]
 hci_devcd_dump+0x142/0x240 net/bluetooth/coredump.c:258
 hci_devcd_timeout+0xb5/0x2e0 net/bluetooth/coredump.c:413
 process_one_work+0x9cc/0x1b70 kernel/workqueue.c:3238
 process_scheduled_works kernel/workqueue.c:3319 [inline]
 worker_thread+0x6c8/0xf10 kernel/workqueue.c:3400
 kthread+0x3c2/0x780 kernel/kthread.c:464
 ret_from_fork+0x45/0x80 arch/x86/kernel/process.c:153
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>

The buggy address ffffc90004ed5000 belongs to a vmalloc virtual mapping
Memory state around the buggy address:
 ffffc90004ed4f00: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
 ffffc90004ed4f80: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
>ffffc90004ed5000: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
                   ^
 ffffc90004ed5080: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
 ffffc90004ed5100: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
==================================================================

To avoid this issue, reorder devcoredumpv to be called after skbput_data that does not free the data.