[PATCH net 0/2] vsock: fix null pointer dereference and cleanup in vsock_poll()

[PATCH net 0/2] vsock: fix null pointer dereference and cleanup in vsock_poll()

[Stefano Garzarella]

The first patch fixes a potential null pointer dereference in vsock_poll()
reported by syzbot.
The second patch is a simple cleanup in the same block code. I put this later,
to make it easier to backport the first patch in the stable branches.

Thanks,
Stefano

Stefano Garzarella (2):
  vsock: fix potential null pointer dereference in vsock_poll()
  vsock: small cleanup in vsock_poll()

 net/vmw_vsock/af_vsock.c | 27 ++++++++++++---------------
 1 file changed, 12 insertions(+), 15 deletions(-)

-- 
2.26.2

[PATCH net 1/2] vsock: fix potential null pointer dereference in vsock_poll()

[Stefano Garzarella]

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>
---
 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

[PATCH net 2/2] vsock: small cleanup in vsock_poll()

[Stefano Garzarella]

This patch combines nested if statements in a single one to reduce
the indentation in vsock_poll().
It also combines an if nested in the else branch.

The behavior isn't changed.

Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
---
 net/vmw_vsock/af_vsock.c | 27 ++++++++++++---------------
 1 file changed, 12 insertions(+), 15 deletions(-)

diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
index 9e93bc201cc0..2c80dc14fa60 100644
--- a/net/vmw_vsock/af_vsock.c
+++ b/net/vmw_vsock/af_vsock.c
@@ -1032,21 +1032,18 @@ static __poll_t vsock_poll(struct file *file, struct socket *sock,
 		}
 
 		/* Connected sockets that can produce data can be written. */
-		if (transport && sk->sk_state == TCP_ESTABLISHED) {
-			if (!(sk->sk_shutdown & SEND_SHUTDOWN)) {
-				bool space_avail_now = false;
-				int ret = transport->notify_poll_out(
-						vsk, 1, &space_avail_now);
-				if (ret < 0) {
-					mask |= EPOLLERR;
-				} else {
-					if (space_avail_now)
-						/* Remove EPOLLWRBAND since INET
-						 * sockets are not setting it.
-						 */
-						mask |= EPOLLOUT | EPOLLWRNORM;
-
-				}
+		if (transport && sk->sk_state == TCP_ESTABLISHED &&
+		    !(sk->sk_shutdown & SEND_SHUTDOWN)) {
+			bool space_avail_now = false;
+			int ret = transport->notify_poll_out(vsk, 1,
+							     &space_avail_now);
+			if (ret < 0) {
+				mask |= EPOLLERR;
+			} else if (space_avail_now) {
+				/* Remove EPOLLWRBAND since INET
+				 * sockets are not setting it.
+				 */
+				mask |= EPOLLOUT | EPOLLWRNORM;
 			}
 		}
 
-- 
2.26.2

Re: [PATCH net 0/2] vsock: fix null pointer dereference and cleanup in vsock_poll()

[David Miller]

From: Stefano Garzarella <sgarzare@redhat.com>
Date: Tue, 11 Aug 2020 11:55:02 +0200

> The first patch fixes a potential null pointer dereference in vsock_poll()
> reported by syzbot.
> The second patch is a simple cleanup in the same block code. I put this later,
> to make it easier to backport the first patch in the stable branches.

Please do not mix cleanups and bug fixes into the same patch series.

net-next is closed, so you should not be submitting non-bugfixes at
this time.

Re: [PATCH net 0/2] vsock: fix null pointer dereference and cleanup in vsock_poll()

[Stefano Garzarella]

On Tue, Aug 11, 2020 at 10:24:18AM -0700, David Miller wrote:
> From: Stefano Garzarella <sgarzare@redhat.com>
> Date: Tue, 11 Aug 2020 11:55:02 +0200
> 
> > The first patch fixes a potential null pointer dereference in vsock_poll()
> > reported by syzbot.
> > The second patch is a simple cleanup in the same block code. I put this later,
> > to make it easier to backport the first patch in the stable branches.
> 
> Please do not mix cleanups and bug fixes into the same patch series.

I did it because I was going through the same part of the code,
but I won't do it again!

> 
> net-next is closed, so you should not be submitting non-bugfixes at
> this time.
> 

I'll resend only the first patch, sorry for the noise.

Thanks,
Stefano