Re: [Linux-kernel-mentees] [PATCH v4 net] rose: Fix Null pointer dereference in rose_send_frame()
From: Jakub Kicinski <kuba@kernel.org>
Date: 2020-11-14 19:19:03
Also in:
linux-hams, linux-kernel-mentees, lkml
Subsystem:
networking [general], the rest · Maintainers:
"David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Linus Torvalds
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 <redacted>quoted hunk ↗ jump to hunk
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.