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SubjectRe: [Linux-kernel-mentees] [PATCH] net: bluetooth: Fix null pointer dereference in hci_event_packet()
On Thu, Sep 10, 2020 at 01:49:18PM +0300, Dan Carpenter wrote:
> On Thu, Sep 10, 2020 at 10:04:24AM +0530, Anmol Karn wrote:
> > Prevent hci_phy_link_complete_evt() from dereferencing 'hcon->amp_mgr'
> > as NULL. Fix it by adding pointer check for it.
> >
> > Reported-and-tested-by: syzbot+0bef568258653cff272f@syzkaller.appspotmail.com
> > Link: https://syzkaller.appspot.com/bug?extid=0bef568258653cff272f
> > Signed-off-by: Anmol Karn <anmol.karan123@gmail.com>
> > ---
> > net/bluetooth/hci_event.c | 5 +++++
> > 1 file changed, 5 insertions(+)
> >
> > diff --git a/net/bluetooth/hci_event.c b/net/bluetooth/hci_event.c
> > index 4b7fc430793c..871e16804433 100644
> > --- a/net/bluetooth/hci_event.c
> > +++ b/net/bluetooth/hci_event.c
> > @@ -4936,6 +4936,11 @@ static void hci_phy_link_complete_evt(struct hci_dev *hdev,
> > return;
> > }
> >
> > + if (IS_ERR_OR_NULL(hcon->amp_mgr)) {
>
> It can't be an error pointer. Shouldn't we call hci_conn_del() on this
> path? Try to find the Fixes tag to explain how this bug was introduced.
>
> (Don't rush to send a v2. The patch requires quite a bit more digging
> and detective work before it is ready).
>
> > + hci_dev_unlock(hdev);
> > + return;
> > + }
> > +
> > if (ev->status) {
> > hci_conn_del(hcon);
> > hci_dev_unlock(hdev);
>
> regards,
> dan carpenter
>

Sir,

I need little advice in continuing with this Patch,

I have looked into the Bisected logs and the problem occurs from this commit:

941992d29447 ("ethernet: amd: use IS_ENABLED() instead of checking for built-in or module")


Here is a diff of patch which i modified from last patch,

diff --git a/net/bluetooth/hci_event.c b/net/bluetooth/hci_event.c
index 4b7fc430793c..6ce435064e0b 100644
--- a/net/bluetooth/hci_event.c
+++ b/net/bluetooth/hci_event.c
@@ -4936,6 +4936,12 @@ static void hci_phy_link_complete_evt(struct hci_dev *hdev,
return;
}

+ if (!hcon->amp_mgr) {
+ hci_conn_del(hcon);
+ hci_dev_unlock(hdev);
+ return;
+ }
+
if (ev->status) {
hci_conn_del(hcon);
hci_dev_unlock(hdev);

The value of 'hcon->amp_mgr' getting NULL due to hci_conn_hash_lookup_handle call
, and there is not any checks there for the members of hcon, which enables
hci_phy_link_complete_evt() to dereference 'hcon->amp_mgr' as NULL.

please suggest improvements to this patch.

Regards,
Anmol

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