[PATCH] Fix invalid-free in bcsp_close()

[Tomas Bortoli]

Syzbot reported an invalid-free that I introduced fixing a memleak.

bcsp_recv() also frees bcsp->rx_skb but never nullifies its value.
Nullify bcsp->rx_skb every time it is freed.

Signed-off-by: Tomas Bortoli <tomasb...@gmail.com>
Reported-by: syzbot+a0d209...@syzkaller.appspotmail.com
---
drivers/bluetooth/hci_bcsp.c | 3 +++
1 file changed, 3 insertions(+)

diff --git a/drivers/bluetooth/hci_bcsp.c b/drivers/bluetooth/hci_bcsp.c
index fe2e307009f4..cf4a56095817 100644
--- a/drivers/bluetooth/hci_bcsp.c
+++ b/drivers/bluetooth/hci_bcsp.c
@@ -591,6 +591,7 @@ static int bcsp_recv(struct hci_uart *hu, const void *data, int count)
if (*ptr == 0xc0) {
BT_ERR("Short BCSP packet");
kfree_skb(bcsp->rx_skb);
+ bcsp->rx_skb = NULL;
bcsp->rx_state = BCSP_W4_PKT_START;
bcsp->rx_count = 0;
} else
@@ -606,6 +607,7 @@ static int bcsp_recv(struct hci_uart *hu, const void *data, int count)
bcsp->rx_skb->data[2])) != bcsp->rx_skb->data[3]) {
BT_ERR("Error in BCSP hdr checksum");
kfree_skb(bcsp->rx_skb);
+ bcsp->rx_skb = NULL;
bcsp->rx_state = BCSP_W4_PKT_DELIMITER;
bcsp->rx_count = 0;
continue;
@@ -630,6 +632,7 @@ static int bcsp_recv(struct hci_uart *hu, const void *data, int count)
bscp_get_crc(bcsp));

kfree_skb(bcsp->rx_skb);
+ bcsp->rx_skb = NULL;
bcsp->rx_state = BCSP_W4_PKT_DELIMITER;
bcsp->rx_count = 0;
continue;
--
2.20.1

[Marcel Holtmann]

Hi Tomas,

> Syzbot reported an invalid-free that I introduced fixing a memleak.
>
> bcsp_recv() also frees bcsp->rx_skb but never nullifies its value.
> Nullify bcsp->rx_skb every time it is freed.
>
> Signed-off-by: Tomas Bortoli <tomasb...@gmail.com>
> Reported-by: syzbot+a0d209...@syzkaller.appspotmail.com
> ---
> drivers/bluetooth/hci_bcsp.c | 3 +++
> 1 file changed, 3 insertions(+)

patch has been applied to bluetooth-next tree.

Regards

Marcel

[Alexander Potapenko]

Hi Tomas, Marcel, Greg,

I believe this bug requires stable tags, as it can potentially provide
an arbitrary write (via __skb_unlink) and is triggerable locally with
user privileges.
> Regards
>
> Marcel
>
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--
Alexander Potapenko
Software Engineer

Google Germany GmbH
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[Marcel Holtmann]

Hi Alexander,

>>> Syzbot reported an invalid-free that I introduced fixing a memleak.
>>>
>>> bcsp_recv() also frees bcsp->rx_skb but never nullifies its value.
>>> Nullify bcsp->rx_skb every time it is freed.
>>>
>>> Signed-off-by: Tomas Bortoli <tomasb...@gmail.com>
>>> Reported-by: syzbot+a0d209...@syzkaller.appspotmail.com
>>> ---
>>> drivers/bluetooth/hci_bcsp.c | 3 +++
>>> 1 file changed, 3 insertions(+)
>>
>> patch has been applied to bluetooth-next tree.
> I believe this bug requires stable tags, as it can potentially provide
> an arbitrary write (via __skb_unlink) and is triggerable locally with
> user privileges.

I do not have a reproducer for it, but if you do, feel free to propose it for -stable inclusion.

Regards

Marcel

[Greg Kroah-Hartman]

Now queued up, thanks.

greg k-h