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Message-ID: <2cacbbf0-0e7b-410f-9ca1-b4542e0d51d4@molgen.mpg.de>
Date: Fri, 18 Jul 2025 09:41:58 +0200
From: Paul Menzel <pmenzel@...gen.mpg.de>
To: Ivan Pravdin <ipravdin.official@...il.com>
Cc: marcel@...tmann.org, johan.hedberg@...il.com, luiz.dentz@...il.com,
linux-bluetooth@...r.kernel.org, linux-kernel@...r.kernel.org,
syzbot+ac3c79181f6aecc5120c@...kaller.appspotmail.com
Subject: Re: [PATCH] Bluetooth: hci_devcd_dump: fix out-of-bounds via
dev_coredumpv
Dear Ivan,
Thank you for your patch.
Am 17.07.25 um 17:10 schrieb Ivan Pravdin:
> 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.
Should you resend, the lines do not need to be intended, that means the
> should be at the very beginning.
> 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.
>
> Reported-by: syzbot+ac3c79181f6aecc5120c@...kaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=ac3c79181f6aecc5120c
> Fixes: b257e02ecc46 ("HCI: coredump: Log devcd dumps into the monitor")
> Tested-by: syzbot+ac3c79181f6aecc5120c@...kaller.appspotmail.com
> Signed-off-by: Ivan Pravdin <ipravdin.official@...il.com>
> ---
>
> Changes since v2:
> * Updated subject line
> * Updated comment to include more details about the issue
> * Moved dev_coredumpv instead of using temporary buffer
>
> Changes since v1:
> * Changed subject prefix to Bluetooth:
>
> [v2] https://lore.kernel.org/linux-bluetooth/20250716003726.124975-2-ipravdin.official@gmail.com/
> [v1] https://lore.kernel.org/linux-bluetooth/20250614041910.219584-1-ipravdin.official@gmail.com/
One minor thing, *v3* is missing in the tag in summary, so it’d be
[PATCH v3]. `git format-patch -v3` should accomplish this.
> net/bluetooth/coredump.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/net/bluetooth/coredump.c b/net/bluetooth/coredump.c
> index 819eacb38762..720cb79adf96 100644
> --- a/net/bluetooth/coredump.c
> +++ b/net/bluetooth/coredump.c
> @@ -249,15 +249,15 @@ static void hci_devcd_dump(struct hci_dev *hdev)
>
> size = hdev->dump.tail - hdev->dump.head;
>
> - /* Emit a devcoredump with the available data */
> - dev_coredumpv(&hdev->dev, hdev->dump.head, size, GFP_KERNEL);
> -
> /* Send a copy to monitor as a diagnostic packet */
> skb = bt_skb_alloc(size, GFP_ATOMIC);
> if (skb) {
> skb_put_data(skb, hdev->dump.head, size);
> hci_recv_diag(hdev, skb);
> }
> +
> + /* Emit a devcoredump with the available data */
> + dev_coredumpv(&hdev->dev, hdev->dump.head, size, GFP_KERNEL);
> }
>
> static void hci_devcd_handle_pkt_complete(struct hci_dev *hdev,
Reviewed-by: Paul Menzel <pmenzel@...gen.mpg.de>
Kind regards,
Paul
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