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Date: Wed, 29 Jun 2022 11:48:30 +0800 (GMT+08:00)
From: duoming@....edu.cn
To: "Paolo Abeni" <pabeni@...hat.com>
Cc: linux-hams@...r.kernel.org, ralf@...ux-mips.org,
davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net v3 2/2] net: rose: fix null-ptr-deref caused by
rose_kill_by_neigh
Hello,
On Tue, 28 Jun 2022 13:12:40 +0200 Paolo Abeni wrote:
> > When the link layer connection is broken, the rose->neighbour is
> > set to null. But rose->neighbour could be used by rose_connection()
> > and rose_release() later, because there is no synchronization among
> > them. As a result, the null-ptr-deref bugs will happen.
> >
> > One of the null-ptr-deref bugs is shown below:
> >
> > (thread 1) | (thread 2)
> > | rose_connect
> > rose_kill_by_neigh | lock_sock(sk)
> > spin_lock_bh(&rose_list_lock) | if (!rose->neighbour)
> > rose->neighbour = NULL;//(1) |
> > | rose->neighbour->use++;//(2)
> >
> > The rose->neighbour is set to null in position (1) and dereferenced
> > in position (2).
> >
> > The KASAN report triggered by POC is shown below:
> >
> > KASAN: null-ptr-deref in range [0x0000000000000028-0x000000000000002f]
> > ...
> > RIP: 0010:rose_connect+0x6c2/0xf30
> > RSP: 0018:ffff88800ab47d60 EFLAGS: 00000206
> > RAX: 0000000000000005 RBX: 000000000000002a RCX: 0000000000000000
> > RDX: ffff88800ab38000 RSI: ffff88800ab47e48 RDI: ffff88800ab38309
> > RBP: dffffc0000000000 R08: 0000000000000000 R09: ffffed1001567062
> > R10: dfffe91001567063 R11: 1ffff11001567061 R12: 1ffff11000d17cd0
> > R13: ffff8880068be680 R14: 0000000000000002 R15: 1ffff11000d17cd0
> > ...
> > Call Trace:
> > <TASK>
> > ? __local_bh_enable_ip+0x54/0x80
> > ? selinux_netlbl_socket_connect+0x26/0x30
> > ? rose_bind+0x5b0/0x5b0
> > __sys_connect+0x216/0x280
> > __x64_sys_connect+0x71/0x80
> > do_syscall_64+0x43/0x90
> > entry_SYSCALL_64_after_hwframe+0x46/0xb0
> >
> > This patch adds lock_sock() in rose_kill_by_neigh() in order to
> > synchronize with rose_connect() and rose_release().
> >
> > Meanwhile, this patch adds sock_hold() protected by rose_list_lock
> > that could synchronize with rose_remove_socket() in order to mitigate
> > UAF bug caused by lock_sock() we add.
> >
> > What's more, there is no need using rose_neigh_list_lock to protect
> > rose_kill_by_neigh(). Because we have already used rose_neigh_list_lock
> > to protect the state change of rose_neigh in rose_link_failed(), which
> > is well synchronized.
> >
> > Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> > Signed-off-by: Duoming Zhou <duoming@....edu.cn>
> > ---
> > Changes since v2:
> > - v2: Fix refcount leak of sock.
> >
> > net/rose/af_rose.c | 6 ++++++
> > net/rose/rose_route.c | 2 ++
> > 2 files changed, 8 insertions(+)
> >
> > diff --git a/net/rose/af_rose.c b/net/rose/af_rose.c
> > index bf2d986a6bc..5caa222c490 100644
> > --- a/net/rose/af_rose.c
> > +++ b/net/rose/af_rose.c
> > @@ -169,9 +169,15 @@ void rose_kill_by_neigh(struct rose_neigh *neigh)
> > struct rose_sock *rose = rose_sk(s);
> >
> > if (rose->neighbour == neigh) {
> > + sock_hold(s);
> > rose_disconnect(s, ENETUNREACH, ROSE_OUT_OF_ORDER, 0);
> > rose->neighbour->use--;
> > + spin_unlock_bh(&rose_list_lock);
> > + lock_sock(s);
> > rose->neighbour = NULL;
> > + release_sock(s);
> > + spin_lock_bh(&rose_list_lock);
>
> I'm sorry, I likely was not clear enough in my previous reply. This is
> broken. If a list is [spin_]lock protected, you can't release the lock,
> reacquire it and continue traversing the list from the [now invalid]
> same iterator.
>
> e.g. if s is removed from the list, even if the sock is not de-
> allocated due to the addtional refcount, the traversing will errnously
> stop after this sock, instead of continuing processing the remaining
> socks in the list.
I understand. The following is a new solution:
diff --git a/net/rose/af_rose.c b/net/rose/af_rose.c
index bf2d986a6bc..24dcbde88fb 100644
--- a/net/rose/af_rose.c
+++ b/net/rose/af_rose.c
@@ -165,13 +165,21 @@ void rose_kill_by_neigh(struct rose_neigh *neigh)
struct sock *s;
spin_lock_bh(&rose_list_lock);
+again:
sk_for_each(s, &rose_list) {
struct rose_sock *rose = rose_sk(s);
if (rose->neighbour == neigh) {
+ sock_hold(s);
+ spin_unlock_bh(&rose_list_lock);
+ lock_sock(s);
rose_disconnect(s, ENETUNREACH, ROSE_OUT_OF_ORDER, 0);
rose->neighbour->use--;
rose->neighbour = NULL;
+ release_sock(s);
+ spin_lock_bh(&rose_list_lock);
+ sock_put(s);
+ goto again;
}
}
spin_unlock_bh(&rose_list_lock);
diff --git a/net/rose/rose_route.c b/net/rose/rose_route.c
index fee6409c2bb..b116828b422 100644
--- a/net/rose/rose_route.c
+++ b/net/rose/rose_route.c
@@ -827,7 +827,9 @@ void rose_link_failed(ax25_cb *ax25, int reason)
ax25_cb_put(ax25);
rose_del_route_by_neigh(rose_neigh);
+ spin_unlock_bh(&rose_neigh_list_lock);
rose_kill_by_neigh(rose_neigh);
+ return;
}
spin_unlock_bh(&rose_neigh_list_lock);
}
If s is removed from the list, the traversing will not stop erroneously.
Best regards,
Duoming Zhou
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