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[146.241.106.148]) by smtp.gmail.com with ESMTPSA id w8-20020a1cf608000000b0039c5a765388sm22308049wmc.28.2022.07.05.01.43.45 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 05 Jul 2022 01:43:45 -0700 (PDT) Message-ID: <4a95703c5c1a09e3ed1a64ddf83e65e222326214.camel@redhat.com> Subject: Re: [PATCH net v5] net: rose: fix null-ptr-deref caused by rose_kill_by_neigh From: Paolo Abeni To: Duoming Zhou , linux-hams@vger.kernel.org Cc: ralf@linux-mips.org, davem@davemloft.net, edumazet@google.com, kuba@kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org Date: Tue, 05 Jul 2022 10:43:44 +0200 In-Reply-To: <20220702075718.25121-1-duoming@zju.edu.cn> References: <20220702075718.25121-1-duoming@zju.edu.cn> Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.42.4 (3.42.4-2.fc35) MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, 2022-07-02 at 15:57 +0800, Duoming Zhou 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: > > ? __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 > --- > Changes in v5: > - v5: Use socket lock to protect comparison in rose_kill_by_neigh. > > net/rose/af_rose.c | 12 ++++++++++++ > net/rose/rose_route.c | 2 ++ > 2 files changed, 14 insertions(+) > > diff --git a/net/rose/af_rose.c b/net/rose/af_rose.c > index bf2d986a6bc..6d5088b030a 100644 > --- a/net/rose/af_rose.c > +++ b/net/rose/af_rose.c > @@ -165,14 +165,26 @@ 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); > > + sock_hold(s); > + spin_unlock_bh(&rose_list_lock); > + lock_sock(s); > if (rose->neighbour == neigh) { > rose_disconnect(s, ENETUNREACH, ROSE_OUT_OF_ORDER, 0); > rose->neighbour->use--; Note that the code can held different socket lock while updating 'neighbour->use'. That really means that such updates can really race each other, with bad results. I think the only safe way out is using an atomic_t for 'neighbour->use' (likely a refcount_t would be a better option). All the above deserves a separate patch IMHO. > rose->neighbour = NULL; > + release_sock(s); > + sock_put(s); > + spin_lock_bh(&rose_list_lock); > + goto again; This chunk is dup of the following lines, it could be dropped... > } > + release_sock(s); > + sock_put(s); > + spin_lock_bh(&rose_list_lock); > + goto again; ... if this would be correct, which apparently is not. What happens when 'rose->neighbour' is different from 'neigh' for first socket in rose_list? Cheers, Paolo