Hi,
On Sun, Mar 27, 2022 at 8:10 PM Xiaomeng Tong <[email protected]> wrote:
>
> If the previous list_for_each_entry_continue_rcu() don't exit early
> (no goto hit inside the loop), the iterator 'cvif' after the loop
> will be a bogus pointer to an invalid structure object containing
> the HEAD (&ar->vif_list). As a result, the use of 'cvif' after that
> will lead to a invalid memory access (i.e., 'cvif->id': the invalid
> pointer dereference when return back to/after the callsite in the
> carl9170_update_beacon()).
>
> The original intention should have been to return the valid 'cvif'
> when found in list, NULL otherwise. So just make 'cvif' NULL when
> no entry found, to fix this bug.
>
> Cc: [email protected]
> Fixes: 1f1d9654e183c ("carl9170: refactor carl9170_update_beacon")
> Signed-off-by: Xiaomeng Tong <[email protected]>
> ---
> drivers/net/wireless/ath/carl9170/tx.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/drivers/net/wireless/ath/carl9170/tx.c b/drivers/net/wireless/ath/carl9170/tx.c
> index 1b76f4434c06..2b8084121001 100644
> --- a/drivers/net/wireless/ath/carl9170/tx.c
> +++ b/drivers/net/wireless/ath/carl9170/tx.c
> @@ -1558,6 +1558,9 @@ static struct carl9170_vif_info *carl9170_pick_beaconing_vif(struct ar9170 *ar)
> goto out;
> }
> } while (ar->beacon_enabled && i--);
> +
> + /* no entry found in list */
> + cvif = NULL;
> }
>
> out:
hmm, It's really not easy test this. There are multiple locks, device
states and flags to consider.
the state of the protecting ar->vifs > 0 (I guess this could be > 1.
There's no point in being choosy
about "picky choices", if there's only one), the main virtual
interface as well as cvif->enable_beacon
and ar->beacon_enable don't change on a whim.
But it it is true that this function gets called by the firmware as a
callback to the TBTT,
so it would warrant any protection that is possible. Whenever a bug
can happen or be
forced in this case: I don't know, I can't do experiments until much
later (easter :( ).
But it's better and easy to err on the side of caution.
Note: That "cvif = NULL;" will certainly break the beaconing for good
(for the remaining
lifetime of the main interface). The driver would need to be stopped
and restarted before
beaconing would work again. A safer choice would be to return NULL;
That said, if the
bug can happen, the driver/firmware would be in a bad state at that
point anyway.
So a call to carl9170_restart(ar, ...there's no code for a
driver/firmware mismatch yet) will
be necessary in the hope that this was just a temporary glitch.
Cheers,
Christian
On Sun, 27 Mar 2022 23:40:46 +0200, Christian Lamparter wrote:
> On Sun, Mar 27, 2022 at 8:10 PM Xiaomeng Tong <[email protected]> wrote:
> >
> > If the previous list_for_each_entry_continue_rcu() don't exit early
> > (no goto hit inside the loop), the iterator 'cvif' after the loop
> > will be a bogus pointer to an invalid structure object containing
> > the HEAD (&ar->vif_list). As a result, the use of 'cvif' after that
> > will lead to a invalid memory access (i.e., 'cvif->id': the invalid
> > pointer dereference when return back to/after the callsite in the
> > carl9170_update_beacon()).
> >
> > The original intention should have been to return the valid 'cvif'
> > when found in list, NULL otherwise. So just make 'cvif' NULL when
> > no entry found, to fix this bug.
> >
> > Cc: [email protected]
> > Fixes: 1f1d9654e183c ("carl9170: refactor carl9170_update_beacon")
> > Signed-off-by: Xiaomeng Tong <[email protected]>
> > ---
> > drivers/net/wireless/ath/carl9170/tx.c | 3 +++
> > 1 file changed, 3 insertions(+)
> >
> > diff --git a/drivers/net/wireless/ath/carl9170/tx.c b/drivers/net/wireless/ath/carl9170/tx.c
> > index 1b76f4434c06..2b8084121001 100644
> > --- a/drivers/net/wireless/ath/carl9170/tx.c
> > +++ b/drivers/net/wireless/ath/carl9170/tx.c
> > @@ -1558,6 +1558,9 @@ static struct carl9170_vif_info *carl9170_pick_beaconing_vif(struct ar9170 *ar)
> > goto out;
> > }
> > } while (ar->beacon_enabled && i--);
> > +
> > + /* no entry found in list */
> > + cvif = NULL;
> > }
> >
> > out:
>
> hmm, It's really not easy test this. There are multiple locks, device
> states and flags to consider.
> the state of the protecting ar->vifs > 0 (I guess this could be > 1.
> There's no point in being choosy
> about "picky choices", if there's only one), the main virtual
> interface as well as cvif->enable_beacon
> and ar->beacon_enable don't change on a whim.
>
> But it it is true that this function gets called by the firmware as a
> callback to the TBTT,
> so it would warrant any protection that is possible. Whenever a bug
> can happen or be
> forced in this case: I don't know, I can't do experiments until much
> later (easter :( ).
> But it's better and easy to err on the side of caution.
>
> Note: That "cvif = NULL;" will certainly break the beaconing for good
> (for the remaining
> lifetime of the main interface). The driver would need to be stopped
> and restarted before
> beaconing would work again. A safer choice would be to return NULL;
> That said, if the
> bug can happen, the driver/firmware would be in a bad state at that
> point anyway.
> So a call to carl9170_restart(ar, ...there's no code for a
> driver/firmware mismatch yet) will
> be necessary in the hope that this was just a temporary glitch.
Thank you, i have resubmitted a v2 patch as you suggested: just return NULL
to fix it. Please check it.
--
Xiaomeng Tong