[Linux-kernel-mentees] [PATCH net] ipvs: Fix uninit-value in do_ip_vs_set_ctl()

do_ip_vs_set_ctl() is referencing uninitialized stack value when `len` is
zero. Fix it.

Reported-and-tested-by: syzbot+23b5f9e7caf61d9a3898@syzkaller.appspotmail.com
Link: https://syzkaller.appspot.com/bug?id=46ebfb92a8a812621a001ef04d90dfa459520fe2
Signed-off-by: Peilin Ye <redacted>
---
 net/netfilter/ipvs/ip_vs_ctl.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/netfilter/ipvs/ip_vs_ctl.c b/net/netfilter/ipvs/ip_vs_ctl.c
index 412656c34f20..c050b6a42786 100644
--- a/net/netfilter/ipvs/ip_vs_ctl.c
+++ b/net/netfilter/ipvs/ip_vs_ctl.c

@@ -2418,7 +2418,7 @@ do_ip_vs_set_ctl(struct sock *sk, int cmd, void __user *user, unsigned int len)
 {
 	struct net *net = sock_net(sk);
 	int ret;
-	unsigned char arg[MAX_SET_ARGLEN];
+	unsigned char arg[MAX_SET_ARGLEN] = {};
 	struct ip_vs_service_user *usvc_compat;
 	struct ip_vs_service_user_kern usvc;
 	struct ip_vs_service *svc;

-- 
2.25.1

On Mon, Aug 10, 2020 at 3:10 PM Peilin Ye [off-list ref] wrote:

do_ip_vs_set_ctl() is referencing uninitialized stack value when `len` is
zero. Fix it.

Which exact 'cmd' is it here?

I _guess_ it is one of those uninitialized in set_arglen[], which is 0.
But if that is the case, should it be initialized to
sizeof(struct ip_vs_service_user) instead because ip_vs_copy_usvc_compat()
is called anyway. Or, maybe we should just ban len==0 case.

In either case, it does not look like you fix it correctly.

Thanks.

On Mon, Aug 10, 2020 at 08:57:19PM -0700, Cong Wang wrote:

On Mon, Aug 10, 2020 at 3:10 PM Peilin Ye [off-list ref] wrote:

quoted

do_ip_vs_set_ctl() is referencing uninitialized stack value when `len` is
zero. Fix it.

Which exact 'cmd' is it here?

I _guess_ it is one of those uninitialized in set_arglen[], which is 0.

Yes, it was `IP_VS_SO_SET_NONE`, implicitly initialized to zero.

But if that is the case, should it be initialized to
sizeof(struct ip_vs_service_user) instead because ip_vs_copy_usvc_compat()
is called anyway. Or, maybe we should just ban len==0 case.

I see. I think the latter would be easier, but we cannot ban all of
them, since the function does something with `IP_VS_SO_SET_FLUSH`, which
is a `len == 0` case.

Maybe we do something like this?

@@ -2432,6 +2432,8 @@ do_ip_vs_set_ctl(struct sock *sk, int cmd, void __user *user, unsigned int len)

 	if (cmd < IP_VS_BASE_CTL || cmd > IP_VS_SO_SET_MAX)
 		return -EINVAL;
+	if (len == 0 && cmd != IP_VS_SO_SET_FLUSH)
+		return -EINVAL;
 	if (len != set_arglen[CMDID(cmd)]) {
 		IP_VS_DBG(1, "set_ctl: len %u != %u\n",
 			  len, set_arglen[CMDID(cmd)]);

@@ -2547,9 +2549,6 @@ do_ip_vs_set_ctl(struct sock *sk, int cmd, void __user *user, unsigned int len)
 		break;
 	case IP_VS_SO_SET_DELDEST:
 		ret = ip_vs_del_dest(svc, &udest);
-		break;
-	default:
-		ret = -EINVAL;
 	}

   out_unlock:

Thank you,
Peilin Ye

In either case, it does not look like you fix it correctly.

Thanks.

	Hello,

On Tue, 11 Aug 2020, Peilin Ye wrote:

On Mon, Aug 10, 2020 at 08:57:19PM -0700, Cong Wang wrote:

quoted

On Mon, Aug 10, 2020 at 3:10 PM Peilin Ye [off-list ref] wrote:

quoted

do_ip_vs_set_ctl() is referencing uninitialized stack value when `len` is
zero. Fix it.

Which exact 'cmd' is it here?

I _guess_ it is one of those uninitialized in set_arglen[], which is 0.

Yes, it was `IP_VS_SO_SET_NONE`, implicitly initialized to zero.

quoted

But if that is the case, should it be initialized to
sizeof(struct ip_vs_service_user) instead because ip_vs_copy_usvc_compat()
is called anyway. Or, maybe we should just ban len==0 case.

I see. I think the latter would be easier, but we cannot ban all of
them, since the function does something with `IP_VS_SO_SET_FLUSH`, which
is a `len == 0` case.

Maybe we do something like this?

	Yes, only IP_VS_SO_SET_FLUSH uses len 0. We can go with
this change but you do not need to target net tree, as the
problem is not fatal net-next works too. What happens is
that we may lookup services with random search keys which
is harmless.

	Another option is to add new block after this one:

        } else if (cmd == IP_VS_SO_SET_TIMEOUT) {
                /* Set timeout values for (tcp tcpfin udp) */
                ret = ip_vs_set_timeout(ipvs, (struct ip_vs_timeout_user *)arg);
                goto out_unlock;
        }

	such as:

	} else if (!len) {
		/* No more commands with len=0 below */
		ret = -EINVAL;
		goto out_unlock;
	}

	It give more chance for future commands to use len=0
but the drawback is that the check happens under mutex. So, I'm
fine with both versions, it is up to you to decide :)

Regards

--
Julian Anastasov [off-list ref]

On Tue, Aug 11, 2020 at 09:58:46AM +0300, Julian Anastasov wrote:

	Hello,

On Tue, 11 Aug 2020, Peilin Ye wrote:

quoted

On Mon, Aug 10, 2020 at 08:57:19PM -0700, Cong Wang wrote:

quoted

On Mon, Aug 10, 2020 at 3:10 PM Peilin Ye [off-list ref] wrote:

quoted

do_ip_vs_set_ctl() is referencing uninitialized stack value when `len` is
zero. Fix it.

Which exact 'cmd' is it here?

I _guess_ it is one of those uninitialized in set_arglen[], which is 0.

Yes, it was `IP_VS_SO_SET_NONE`, implicitly initialized to zero.

quoted

But if that is the case, should it be initialized to
sizeof(struct ip_vs_service_user) instead because ip_vs_copy_usvc_compat()
is called anyway. Or, maybe we should just ban len==0 case.

I see. I think the latter would be easier, but we cannot ban all of
them, since the function does something with `IP_VS_SO_SET_FLUSH`, which
is a `len == 0` case.

Maybe we do something like this?

	Yes, only IP_VS_SO_SET_FLUSH uses len 0. We can go with
this change but you do not need to target net tree, as the
problem is not fatal net-next works too. What happens is
that we may lookup services with random search keys which
is harmless.

I see, I'll target net-next instead.

	Another option is to add new block after this one:

        } else if (cmd == IP_VS_SO_SET_TIMEOUT) {
                /* Set timeout values for (tcp tcpfin udp) */
                ret = ip_vs_set_timeout(ipvs, (struct ip_vs_timeout_user *)arg);
                goto out_unlock;
        }

	such as:

	} else if (!len) {
		/* No more commands with len=0 below */
		ret = -EINVAL;
		goto out_unlock;
	}

	It give more chance for future commands to use len=0
but the drawback is that the check happens under mutex. So, I'm
fine with both versions, it is up to you to decide :)

Ah, this seems much cleaner. I'll send v2 soon, thank you!

Peilin Ye

quoted

@@ -2432,6 +2432,8 @@ do_ip_vs_set_ctl(struct sock *sk, int cmd, void __user *user, unsigned int len)

 	if (cmd < IP_VS_BASE_CTL || cmd > IP_VS_SO_SET_MAX)
 		return -EINVAL;
+	if (len == 0 && cmd != IP_VS_SO_SET_FLUSH)
+		return -EINVAL;
 	if (len != set_arglen[CMDID(cmd)]) {
 		IP_VS_DBG(1, "set_ctl: len %u != %u\n",
 			  len, set_arglen[CMDID(cmd)]);

@@ -2547,9 +2549,6 @@ do_ip_vs_set_ctl(struct sock *sk, int cmd, void __user *user, unsigned int len)
 		break;
 	case IP_VS_SO_SET_DELDEST:
 		ret = ip_vs_del_dest(svc, &udest);
-		break;
-	default:
-		ret = -EINVAL;
 	}

   out_unlock:

Regards

--
Julian Anastasov [off-list ref]

do_ip_vs_set_ctl() is referencing uninitialized stack value when `len` is
zero. Fix it.

Reported-by: syzbot+23b5f9e7caf61d9a3898@syzkaller.appspotmail.com
Link: https://syzkaller.appspot.com/bug?id=46ebfb92a8a812621a001ef04d90dfa459520fe2
Suggested-by: Julian Anastasov <ja@ssi.bg>
Signed-off-by: Peilin Ye <redacted>
---
Changes in v2:
    - Target net-next tree. (Suggested by Julian Anastasov [off-list ref])
    - Reject all `len == 0` requests except `IP_VS_SO_SET_FLUSH`, instead
      of initializing `arg`. (Suggested by Cong Wang
      [off-list ref], Julian Anastasov [off-list ref])

 net/netfilter/ipvs/ip_vs_ctl.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/net/netfilter/ipvs/ip_vs_ctl.c b/net/netfilter/ipvs/ip_vs_ctl.c
index 412656c34f20..beeafa42aad7 100644
--- a/net/netfilter/ipvs/ip_vs_ctl.c
+++ b/net/netfilter/ipvs/ip_vs_ctl.c

@@ -2471,6 +2471,10 @@ do_ip_vs_set_ctl(struct sock *sk, int cmd, void __user *user, unsigned int len)
 		/* Set timeout values for (tcp tcpfin udp) */
 		ret = ip_vs_set_timeout(ipvs, (struct ip_vs_timeout_user *)arg);
 		goto out_unlock;
+	} else if (!len) {
+		/* No more commands with len == 0 below */
+		ret = -EINVAL;
+		goto out_unlock;
 	}
 
 	usvc_compat = (struct ip_vs_service_user *)arg;

@@ -2547,9 +2551,6 @@ do_ip_vs_set_ctl(struct sock *sk, int cmd, void __user *user, unsigned int len)
 		break;
 	case IP_VS_SO_SET_DELDEST:
 		ret = ip_vs_del_dest(svc, &udest);
-		break;
-	default:
-		ret = -EINVAL;
 	}
 
   out_unlock:

-- 
2.25.1

	Hello,

On Tue, 11 Aug 2020, Peilin Ye wrote:

do_ip_vs_set_ctl() is referencing uninitialized stack value when `len` is
zero. Fix it.

Reported-by: syzbot+23b5f9e7caf61d9a3898@syzkaller.appspotmail.com
Link: https://syzkaller.appspot.com/bug?id=46ebfb92a8a812621a001ef04d90dfa459520fe2
Suggested-by: Julian Anastasov <ja@ssi.bg>
Signed-off-by: Peilin Ye <redacted>

	Looks good to me, thanks!

Acked-by: Julian Anastasov <ja@ssi.bg>

Regards

--
Julian Anastasov [off-list ref]

On Tue, Aug 11, 2020 at 01:29:04PM +0300, Julian Anastasov wrote:

	Hello,

On Tue, 11 Aug 2020, Peilin Ye wrote:

quoted

do_ip_vs_set_ctl() is referencing uninitialized stack value when `len` is
zero. Fix it.

Reported-by: syzbot+23b5f9e7caf61d9a3898@syzkaller.appspotmail.com
Link: https://syzkaller.appspot.com/bug?id=46ebfb92a8a812621a001ef04d90dfa459520fe2
Suggested-by: Julian Anastasov <ja@ssi.bg>
Signed-off-by: Peilin Ye <redacted>

	Looks good to me, thanks!

Acked-by: Julian Anastasov <ja@ssi.bg>

Pablo, could you consider this for nf-next or should we repost when
net-next re-opens?

Reviewed-by: Simon Horman <horms@verge.net.au>

On Tue, Aug 11, 2020 at 02:59:59PM +0200, Simon Horman wrote:

On Tue, Aug 11, 2020 at 01:29:04PM +0300, Julian Anastasov wrote:

quoted

	Hello,

On Tue, 11 Aug 2020, Peilin Ye wrote:

quoted

do_ip_vs_set_ctl() is referencing uninitialized stack value when `len` is
zero. Fix it.

Reported-by: syzbot+23b5f9e7caf61d9a3898@syzkaller.appspotmail.com
Link: https://syzkaller.appspot.com/bug?id=46ebfb92a8a812621a001ef04d90dfa459520fe2
Suggested-by: Julian Anastasov <ja@ssi.bg>
Signed-off-by: Peilin Ye <redacted>

	Looks good to me, thanks!

Acked-by: Julian Anastasov <ja@ssi.bg>

Pablo, could you consider this for nf-next or should we repost when
net-next re-opens?

No worries, it will sit in netfilter's patchwork until net-next
reopens.

On Tue, Aug 11, 2020 at 03:46:40AM -0400, Peilin Ye wrote:

do_ip_vs_set_ctl() is referencing uninitialized stack value when `len` is
zero. Fix it.

Applied to nf-next, thanks.