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SubjectRE: [PATCH net v2] vsock: fix potential null pointer dereference in vsock_poll()
Date
> From: Stefano Garzarella <sgarzare@redhat.com>
> Sent: Wednesday, August 12, 2020 2:56 PM
> To: davem@davemloft.net
> Cc: linux-kernel@vger.kernel.org; Dexuan Cui <decui@microsoft.com>;
> netdev@vger.kernel.org; Stefan Hajnoczi <stefanha@redhat.com>; Jakub
> Kicinski <kuba@kernel.org>; Jorgen Hansen <jhansen@vmware.com>;
> Stefano Garzarella <sgarzare@redhat.com>
> Subject: [PATCH net v2] vsock: fix potential null pointer dereference in
> vsock_poll()
>
> syzbot reported this issue where in the vsock_poll() we find the
> socket state at TCP_ESTABLISHED, but 'transport' is null:
> general protection fault, probably for non-canonical address
> 0xdffffc0000000012: 0000 [#1] PREEMPT SMP KASAN
> KASAN: null-ptr-deref in range [0x0000000000000090-0x0000000000000097]
> CPU: 0 PID: 8227 Comm: syz-executor.2 Not tainted 5.8.0-rc7-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine,
> BIOS Google 01/01/2011
> RIP: 0010:vsock_poll+0x75a/0x8e0 net/vmw_vsock/af_vsock.c:1038
> Call Trace:
> sock_poll+0x159/0x460 net/socket.c:1266
> vfs_poll include/linux/poll.h:90 [inline]
> do_pollfd fs/select.c:869 [inline]
> do_poll fs/select.c:917 [inline]
> do_sys_poll+0x607/0xd40 fs/select.c:1011
> __do_sys_poll fs/select.c:1069 [inline]
> __se_sys_poll fs/select.c:1057 [inline]
> __x64_sys_poll+0x18c/0x440 fs/select.c:1057
> do_syscall_64+0x60/0xe0 arch/x86/entry/common.c:384
> entry_SYSCALL_64_after_hwframe+0x44/0xa9
>
> This issue can happen if the TCP_ESTABLISHED state is set after we read
> the vsk->transport in the vsock_poll().
>
> We could put barriers to synchronize, but this can only happen during
> connection setup, so we can simply check that 'transport' is valid.
>
> Fixes: c0cfa2d8a788 ("vsock: add multi-transports support")
> Reported-and-tested-by:
> syzbot+a61bac2fcc1a7c6623fe@syzkaller.appspotmail.com
> Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
> ---
> v2:
> - removed cleanups patch from the series [David]
>
> v1:
> https://nam04.safelinks.protection.outlook.com/?url=https%3A%2F%2Fpatc
> hwork.ozlabs.org%2Fproject%2Fnetdev%2Fcover%2F20200811095504.25051-
> 1-
> sgarzare%40redhat.com%2F&amp;data=02%7C01%7Cjhansen%40vmware.co
> m%7C32b3919883a448f56a8708d83ebf1dce%7Cb39138ca3cee4b4aa4d6cd83d
> 9dd62f0%7C0%7C0%7C637328337851992525&amp;sdata=CSo8PEJJwyDE75Qz
> n3lmasJFSNaNChiRXjoy%2FfoJ8Vs%3D&amp;reserved=0
> ---
> net/vmw_vsock/af_vsock.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
> index 27bbcfad9c17..9e93bc201cc0 100644
> --- a/net/vmw_vsock/af_vsock.c
> +++ b/net/vmw_vsock/af_vsock.c
> @@ -1032,7 +1032,7 @@ static __poll_t vsock_poll(struct file *file, struct
> socket *sock,
> }
>
> /* Connected sockets that can produce data can be written.
> */
> - if (sk->sk_state == TCP_ESTABLISHED) {
> + if (transport && sk->sk_state == TCP_ESTABLISHED) {
> if (!(sk->sk_shutdown & SEND_SHUTDOWN)) {
> bool space_avail_now = false;
> int ret = transport->notify_poll_out(
> --
> 2.26.2

Thanks for fixing this!

Reviewed-by: Jorgen Hansen <jhansen@vmware.com>

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