From: Anmol Karn <anmol.karan123@gmail.com>
To: Jakub Kicinski <kuba@kernel.org>
Cc: ralf@linux-mips.org, davem@davemloft.net, saeed@kernel.org,
gregkh@linuxfoundation.org, netdev@vger.kernel.org,
linux-kernel@vger.kernel.org, linux-hams@vger.kernel.org,
linux-kernel-mentees@lists.linuxfoundation.org,
syzkaller-bugs@googlegroups.com,
syzbot+a1c743815982d9496393@syzkaller.appspotmail.com
Subject: Re: [Linux-kernel-mentees] [PATCH v4 net] rose: Fix Null pointer dereference in rose_send_frame()
Date: Sun, 15 Nov 2020 17:14:48 +0530 [thread overview]
Message-ID: <20201115114448.GA40574@Thinkpad> (raw)
In-Reply-To: <20201114111838.03b933af@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
On Sat, Nov 14, 2020 at 11:18:38AM -0800, Jakub Kicinski wrote:
> On Wed, 11 Nov 2020 22:29:54 +0530 Anmol Karn 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@syzkaller.appspotmail.com
> > Tested-by: syzbot+a1c743815982d9496393@syzkaller.appspotmail.com
> > Link: https://syzkaller.appspot.com/bug?id=9d2a7ca8c7f2e4b682c97578dfa3f236258300b3
> > Signed-off-by: Anmol Karn <anmol.karan123@gmail.com>
>
> > diff --git a/net/rose/rose_loopback.c b/net/rose/rose_loopback.c
> > index 7b094275ea8b..6a71b6947d92 100644
> > --- a/net/rose/rose_loopback.c
> > +++ b/net/rose/rose_loopback.c
> > @@ -96,10 +96,12 @@ 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 {
> > + dev_put(dev);
> > kfree_skb(skb);
> > }
> > } else {
>
> This is still not correct. With this code dev_put() could be called with
> NULL, which would cause a crash.
>
> There is also a dev_put() missing if rose_rx_call_request() returns 0.
>
> I think that this is the correct code:
>
> diff --git a/net/rose/rose_loopback.c b/net/rose/rose_loopback.c
> index 7b094275ea8b..ff252ef73592 100644
> --- a/net/rose/rose_loopback.c
> +++ b/net/rose/rose_loopback.c
> @@ -96,11 +96,22 @@ static void rose_loopback_timer(struct timer_list *unused)
> }
>
> if (frametype == ROSE_CALL_REQUEST) {
> - if ((dev = rose_dev_get(dest)) != NULL) {
> - if (rose_rx_call_request(skb, dev, rose_loopback_neigh, lci_o) == 0)
> - kfree_skb(skb);
> - } else {
> + if (!rose_loopback_neigh->dev) {
> kfree_skb(skb);
> + continue;
> + }
> +
> + dev = rose_dev_get(dest);
> + if (!dev) {
> + kfree_skb(skb);
> + continue;
> + }
> +
> + if (rose_rx_call_request(skb, dev, rose_loopback_neigh,
> + lci_o) == 0) {
> + dev_put(dev);
> + kfree_skb(skb);
> }
> } else {
> kfree_skb(skb);
>
> Please test this and resubmit it if it works.
Sure sir, I will test it and resend, if it works.
Thanks,
Anmol
next prev parent reply other threads:[~2020-11-15 11:45 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-05 15:56 [Linux-kernel-mentees] [PATCH v2 net] rose: Fix Null pointer dereference in rose_send_frame() Anmol Karn
2020-11-06 21:04 ` Saeed Mahameed
2020-11-07 8:20 ` Anmol Karn
2020-11-07 19:18 ` [Linux-kernel-mentees] [PATCH v3 " Anmol Karn
2020-11-10 17:58 ` Jakub Kicinski
2020-11-10 19:45 ` Anmol Karn
2020-11-11 16:59 ` [Linux-kernel-mentees] [PATCH v4 " Anmol Karn
2020-11-14 19:18 ` Jakub Kicinski
2020-11-15 11:44 ` Anmol Karn [this message]
2020-11-19 19:10 ` [Linux-kernel-mentees] [PATCH v5 " Anmol Karn
2020-11-20 18:06 ` Jakub Kicinski
2020-11-07 18:56 ` [Linux-kernel-mentees] [PATCH v2] net: " Anmol Karn
2020-11-07 19:02 ` Anmol karn
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