On Wed, Jul 16, 2025 at 10:11:01AM GMT, Luiz Augusto von Dentz wrote: > Hi Ivan, > > On Tue, Jul 15, 2025 at 8:38 PM Ivan Pravdin > <ipravdin.official@xxxxxxxxx> wrote: > > > > Create and use new vmalloc'ed buffer with dev_coredumpv. From > > dev_coredumpv documentation: > > > > `This function takes ownership of the vmalloc'ed data and will free > > it when it is no longer used.` > > > > As hdev->dump is used after dev_coredumpv, create temporary buffer to > > hold hdev->dump data. > > > > Reported-by: syzbot+ac3c79181f6aecc5120c@xxxxxxxxxxxxxxxxxxxxxxxxx > > Closes: https://lore.kernel.org/all/67eaa688.050a0220.1547ec.014a.GAE@xxxxxxxxxx > > It should probably close the syzkaller issue, which I assume is this one: > > https://syzkaller.appspot.com/bug?extid=ac3c79181f6aecc5120c I will change it in v3. > > > Fixes: b257e02ecc46 ("HCI: coredump: Log devcd dumps into the monitor") > > Signed-off-by: Ivan Pravdin <ipravdin.official@xxxxxxxxx> > > --- > > v1 -> v2: Changed subject prefix to Bluetooth: > > > > net/bluetooth/coredump.c | 7 ++++++- > > 1 file changed, 6 insertions(+), 1 deletion(-) > > > > diff --git a/net/bluetooth/coredump.c b/net/bluetooth/coredump.c > > index 819eacb38762..1232c9a94f95 100644 > > --- a/net/bluetooth/coredump.c > > +++ b/net/bluetooth/coredump.c > > @@ -243,6 +243,7 @@ static void hci_devcd_handle_pkt_pattern(struct hci_dev *hdev, > > static void hci_devcd_dump(struct hci_dev *hdev) > > { > > struct sk_buff *skb; > > + char *coredump; > > u32 size; > > > > bt_dev_dbg(hdev, "state %d", hdev->dump.state); > > @@ -250,7 +251,11 @@ 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); > > + coredump = vmalloc(size); > > + if (coredump) { > > + memcpy(coredump, hdev->dump.head, size); > > + dev_coredumpv(&hdev->dev, coredump, size, GFP_KERNEL); > > + } > > > > > > /* Send a copy to monitor as a diagnostic packet */ > > skb = bt_skb_alloc(size, GFP_ATOMIC); > > -- > > 2.45.2 > > > > What is wrong here the is code that attempt to send a copy to the > monitor uses dump.head _after_ dev_coredumpv has freed it, so just > changing the order shall make it work properly: > > 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 Unfortunately this does not work. This was my initial attempt but it still reproduces the error [2]. The reason for that is that dev_coredumpv takes the ownership of the buffer. From the comment above dev_coredumpm_timeout (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 hci_devcd_dump is called multiple times, first time hdev->dump.head will be kept. However, calling hci_devcd_dump second time before data is read by userspace will free it, leading to uaf error like the one observed in the report. As hci_devcd_dump need not be called only one time before hdev is freed, calling it multiple times will lead to uaf, no matter in what order skb_put_data and dev_coredumpv occur in the function. To solve this problem, a temporary buffer should be used. Such buffer should copy data from hdev->dump.head and be surrendered to dev_coredumpv without any possibility to be altered or freed. For reference, here are some examples of using temporary buffer with dev_coredumpv in Intel AVS driver: [bluetoot-next 6f40d15c70bc] sound/soc/intel/avs/apl.c:183 [bluetoot-next 6f40d15c70bc] sound/soc/intel/avs/skl.c:147 [2] https://lore.kernel.org/all/6845dc6b.050a0220.daf97.0af4.GAE@xxxxxxxxxx/ > > > -- > Luiz Augusto von Dentz Thank you for your feedback. Ivan Pravdin
