Messages in this thread | | | Date | Thu, 23 Jun 2022 20:16:36 +0800 (GMT+08:00) | From | duoming@zju ... | Subject | Re: [PATCH net 2/2] net: rose: fix null-ptr-deref caused by rose_kill_by_neigh |
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Hello,
On Thu, 23 Jun 2022 11:30:04 +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@zju.edu.cn> > > --- > > net/rose/af_rose.c | 5 +++++ > > net/rose/rose_route.c | 2 ++ > > 2 files changed, 7 insertions(+) > > > > diff --git a/net/rose/af_rose.c b/net/rose/af_rose.c > > index bf2d986a6bc..dece637e274 100644 > > --- a/net/rose/af_rose.c > > +++ b/net/rose/af_rose.c > > @@ -169,9 +169,14 @@ 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); > > You can't release the lock protecting the list traversal, then re- > acquire it and keep traversing using the same iterator. The list could > be modified in-between.
I think release the lock and then reacquire it is ok. Because we have held the refcount of sock and called rose_disconnect() to change the state of sock with the protection of rose_list_lock which could synchronize with rose_destroy_socket().
If the sock is removed from the list by rose_destroy_socket(), there is no rose->neighbour equals to neigh and the rose_kill_by_neigh() will return.
If there is a rose->neighbour equals to neigh, we held the refcount of sock and called the rose_disconnect() to change the state of it with the protection of rose_list_lock. Even if the sock could be removed from the rose_list by rose_destroy_socket() during the time of unlocking, but the sock will not be deallocated because we have held the refcount of sock. When we reacquire the rose_list_lock, we only do sock_put() in order to deallocate the sock.
@@ -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); + sock_put(s); } } spin_unlock_bh(&rose_list_lock);
> Instead you could build a local list containing the relevant sockets > (under the rose_list_lock protection), additionally acquiring a > reference to each of them > > Then traverse such list outside the rose_list_lock, acquire the socket > lock on each of them, do the neigh clearing and release the reference.
If we build a local list contain the relevant sockets and only acquire a reference to each of them with the protection of rose_list_lock, the socket could be removed by rose_destroy_socket() after we release the rose_list_lock. Then if we traverse such list outside the rose_list_lock we could not find the socket, as a result, the neigh clearing and the refcount releasing operations will not be executed.
Best regards, Duoming Zhou
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