Re: [Linux-kernel-mentees] [PATCH v2] net: rose: Fix Null pointer dereference in rose_send_frame()

[Anmol karn]

Hello,

Sorry for this wrong subject(It should be v3 instead of v2),
please ignore this patch.

I will send a new one with the corrected subject.

Thanks,
Anmol

On Sun, Nov 8, 2020 at 12:27 AM Anmol Karn <anmol.karan123@xxxxxxxxx> wrote:
>
> rose_send_frame() dereferences `neigh->dev` when called from
> rose_transmit_clear_request(), and the first occurrence of the
> `neigh` is in rose_loopback_timer() as `rose_loopback_neigh`,
> and it is initialized in rose_add_loopback_neigh() as NULL.
> i.e when `rose_loopback_neigh` used in rose_loopback_timer()
> its `->dev` was still NULL and rose_loopback_timer() was calling
> rose_rx_call_request() without checking for NULL.
>
> - net/rose/rose_link.c
> This bug seems to get triggered in this line:
>
> rose_call = (ax25_address *)neigh->dev->dev_addr;
>
> Fix it by adding NULL checking for `rose_loopback_neigh->dev`
> in rose_loopback_timer().
>
> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> Reported-by: syzbot+a1c743815982d9496393@xxxxxxxxxxxxxxxxxxxxxxxxx
> Tested-by: syzbot+a1c743815982d9496393@xxxxxxxxxxxxxxxxxxxxxxxxx
> Link: https://syzkaller.appspot.com/bug?id=9d2a7ca8c7f2e4b682c97578dfa3f236258300b3
> Signed-off-by: Anmol Karn <anmol.karan123@xxxxxxxxx>
> ---
> Changes in v3:
>         - Corrected checkpatch warnings and errors (Suggested-by: Saeed Mahameed <saeed@xxxxxxxxxx>)
>         - Added "Fixes:" tag (Suggested-by: Saeed Mahameed <saeed@xxxxxxxxxx>)
> Changes in v2:
>         - Added NULL check in rose_loopback_timer() (Suggested-by: Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx>)
>
>  net/rose/rose_loopback.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/net/rose/rose_loopback.c b/net/rose/rose_loopback.c
> index 7b094275ea8b..2c51756ed7bf 100644
> --- a/net/rose/rose_loopback.c
> +++ b/net/rose/rose_loopback.c
> @@ -96,7 +96,8 @@ static void rose_loopback_timer(struct timer_list *unused)
>                 }
>
>                 if (frametype == ROSE_CALL_REQUEST) {
> -                       if ((dev = rose_dev_get(dest)) != NULL) {
> +                       dev = rose_dev_get(dest);
> +                       if (rose_loopback_neigh->dev && dev) {
>                                 if (rose_rx_call_request(skb, dev, rose_loopback_neigh, lci_o) == 0)
>                                         kfree_skb(skb);
>                         } else {
> -
> 2.29.2
>