In the Linux kernel, the following vulnerability has been resolved: Bluetooth: hci_devcd_dump: fix out-of-bounds via dev_coredumpv Currently both dev_coredumpv and skb_put_data in hci_devcd_dump use hdev->dump.head. However, dev_coredumpv can free the buffer. From dev_coredumpm_timeout 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, dev_coredumpv will discard new buffer, freeing hdev->dump.head. This leads to vmalloc-out-of-bounds error when skb_put_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 dev_coredumpv to be called after skb_put_data that does not free the data.