[PATCH v3 net] netlink: Use copy_to_user() for optval in netlink_getsockopt().

[PATCH v3 net] netlink: Use copy_to_user() for optval in netlink_getsockopt().

[Kuniyuki Iwashima]

Brad Spencer provided a detailed report [0] that when calling getsockopt()
for AF_NETLINK, some SOL_NETLINK options set only 1 byte even though such
options require at least sizeof(int) as length.

The options return a flag value that fits into 1 byte, but such behaviour
confuses users who do not initialise the variable before calling
getsockopt() and do not strictly check the returned value as char.

Currently, netlink_getsockopt() uses put_user() to copy data to optlen and
optval, but put_user() casts the data based on the pointer, char *optval.
As a result, only 1 byte is set to optval.

To avoid this behaviour, we need to use copy_to_user() or cast optval for
put_user().

Note that this changes the behaviour on big-endian systems, but we document
that the size of optval is int in the man page.

  $ man 7 netlink
  ...
  Socket options
       To set or get a netlink socket option, call getsockopt(2) to read
       or setsockopt(2) to write the option with the option level argument
       set to SOL_NETLINK.  Unless otherwise noted, optval is a pointer to
       an int.

Fixes: 9a4595bc7e67 ("[NETLINK]: Add set/getsockopt options to support more than 32 groups")
Fixes: be0c22a46cfb ("netlink: add NETLINK_BROADCAST_ERROR socket option")
Fixes: 38938bfe3489 ("netlink: add NETLINK_NO_ENOBUFS socket flag")
Fixes: 0a6a3a23ea6e ("netlink: add NETLINK_CAP_ACK socket option")
Fixes: 2d4bc93368f5 ("netlink: extended ACK reporting")
Fixes: 89d35528d17d ("netlink: Add new socket option to enable strict checking on dumps")
Reported-by: Brad Spencer <bspencer@blackberry.com>
Link: https://lore.kernel.org/netdev/ZD7VkNWFfp22kTDt@datsun.rim.net/
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
---
v3:
  * Keep errno for unknown opts if len < sizeof(int)
  * Update changelog

v2: https://lore.kernel.org/netdev/20230420233351.77166-1-kuniyu@amazon.com/
  * Keep the len check and setting
  * Update changelog

v1: https://lore.kernel.org/netdev/20230419004246.25770-1-kuniyu@amazon.com/
---
 net/netlink/af_netlink.c | 75 ++++++++++++----------------------------
 1 file changed, 23 insertions(+), 52 deletions(-)

diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index f365dfdd672d..9b6eb28e6e94 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -1742,7 +1742,8 @@ static int netlink_getsockopt(struct socket *sock, int level, int optname,
 {
 	struct sock *sk = sock->sk;
 	struct netlink_sock *nlk = nlk_sk(sk);
-	int len, val, err;
+	unsigned int flag;
+	int len, val;
 
 	if (level != SOL_NETLINK)
 		return -ENOPROTOOPT;
@@ -1754,39 +1755,17 @@ static int netlink_getsockopt(struct socket *sock, int level, int optname,
 
 	switch (optname) {
 	case NETLINK_PKTINFO:
-		if (len < sizeof(int))
-			return -EINVAL;
-		len = sizeof(int);
-		val = nlk->flags & NETLINK_F_RECV_PKTINFO ? 1 : 0;
-		if (put_user(len, optlen) ||
-		    put_user(val, optval))
-			return -EFAULT;
-		err = 0;
+		flag = NETLINK_F_RECV_PKTINFO;
 		break;
 	case NETLINK_BROADCAST_ERROR:
-		if (len < sizeof(int))
-			return -EINVAL;
-		len = sizeof(int);
-		val = nlk->flags & NETLINK_F_BROADCAST_SEND_ERROR ? 1 : 0;
-		if (put_user(len, optlen) ||
-		    put_user(val, optval))
-			return -EFAULT;
-		err = 0;
+		flag = NETLINK_F_BROADCAST_SEND_ERROR;
 		break;
 	case NETLINK_NO_ENOBUFS:
-		if (len < sizeof(int))
-			return -EINVAL;
-		len = sizeof(int);
-		val = nlk->flags & NETLINK_F_RECV_NO_ENOBUFS ? 1 : 0;
-		if (put_user(len, optlen) ||
-		    put_user(val, optval))
-			return -EFAULT;
-		err = 0;
+		flag = NETLINK_F_RECV_NO_ENOBUFS;
 		break;
 	case NETLINK_LIST_MEMBERSHIPS: {
-		int pos, idx, shift;
+		int pos, idx, shift, err = 0;
 
-		err = 0;
 		netlink_lock_table();
 		for (pos = 0; pos * 8 < nlk->ngroups; pos += sizeof(u32)) {
 			if (len - pos < sizeof(u32))
@@ -1803,40 +1782,32 @@ static int netlink_getsockopt(struct socket *sock, int level, int optname,
 		if (put_user(ALIGN(nlk->ngroups / 8, sizeof(u32)), optlen))
 			err = -EFAULT;
 		netlink_unlock_table();
-		break;
+		return err;
 	}
 	case NETLINK_CAP_ACK:
-		if (len < sizeof(int))
-			return -EINVAL;
-		len = sizeof(int);
-		val = nlk->flags & NETLINK_F_CAP_ACK ? 1 : 0;
-		if (put_user(len, optlen) ||
-		    put_user(val, optval))
-			return -EFAULT;
-		err = 0;
+		flag = NETLINK_F_CAP_ACK;
 		break;
 	case NETLINK_EXT_ACK:
-		if (len < sizeof(int))
-			return -EINVAL;
-		len = sizeof(int);
-		val = nlk->flags & NETLINK_F_EXT_ACK ? 1 : 0;
-		if (put_user(len, optlen) || put_user(val, optval))
-			return -EFAULT;
-		err = 0;
+		flag = NETLINK_F_EXT_ACK;
 		break;
 	case NETLINK_GET_STRICT_CHK:
-		if (len < sizeof(int))
-			return -EINVAL;
-		len = sizeof(int);
-		val = nlk->flags & NETLINK_F_STRICT_CHK ? 1 : 0;
-		if (put_user(len, optlen) || put_user(val, optval))
-			return -EFAULT;
-		err = 0;
+		flag = NETLINK_F_STRICT_CHK;
 		break;
 	default:
-		err = -ENOPROTOOPT;
+		return -ENOPROTOOPT;
 	}
-	return err;
+
+	if (len < sizeof(int))
+		return -EINVAL;
+
+	len = sizeof(int);
+	val = nlk->flags & flag ? 1 : 0;
+
+	if (put_user(len, optlen) ||
+	    copy_to_user(optval, &val, len))
+		return -EFAULT;
+
+	return 0;
 }
 
 static void netlink_cmsg_recv_pktinfo(struct msghdr *msg, struct sk_buff *skb)
-- 
2.30.2

Re: [PATCH v3 net] netlink: Use copy_to_user() for optval in netlink_getsockopt().

[David Ahern]

On 4/21/23 12:52 PM, Kuniyuki Iwashima wrote:
> diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
> index f365dfdd672d..9b6eb28e6e94 100644
> --- a/net/netlink/af_netlink.c
> +++ b/net/netlink/af_netlink.c
> @@ -1742,7 +1742,8 @@ static int netlink_getsockopt(struct socket *sock, int level, int optname,
>  {
>  	struct sock *sk = sock->sk;
>  	struct netlink_sock *nlk = nlk_sk(sk);
> -	int len, val, err;
> +	unsigned int flag;
> +	int len, val;

len is not initialized here ...

>  
>  	if (level != SOL_NETLINK)
>  		return -ENOPROTOOPT;
> @@ -1754,39 +1755,17 @@ static int netlink_getsockopt(struct socket *sock, int level, int optname,
>  
>  	switch (optname) {
>  	case NETLINK_PKTINFO:
> -		if (len < sizeof(int))
> -			return -EINVAL;
> -		len = sizeof(int);

you remove all of these ...

> -		val = nlk->flags & NETLINK_F_RECV_PKTINFO ? 1 : 0;
> -		if (put_user(len, optlen) ||
> -		    put_user(val, optval))
> -			return -EFAULT;
> -		err = 0;
> +		flag = NETLINK_F_RECV_PKTINFO;
>  		break;
>  	case NETLINK_BROADCAST_ERROR:
> -		if (len < sizeof(int))
> -			return -EINVAL;
> -		len = sizeof(int);
> -		val = nlk->flags & NETLINK_F_BROADCAST_SEND_ERROR ? 1 : 0;
> -		if (put_user(len, optlen) ||
> -		    put_user(val, optval))
> -			return -EFAULT;
> -		err = 0;
> +		flag = NETLINK_F_BROADCAST_SEND_ERROR;
>  		break;
>  	case NETLINK_NO_ENOBUFS:
> -		if (len < sizeof(int))
> -			return -EINVAL;
> -		len = sizeof(int);
> -		val = nlk->flags & NETLINK_F_RECV_NO_ENOBUFS ? 1 : 0;
> -		if (put_user(len, optlen) ||
> -		    put_user(val, optval))
> -			return -EFAULT;
> -		err = 0;
> +		flag = NETLINK_F_RECV_NO_ENOBUFS;
>  		break;
>  	case NETLINK_LIST_MEMBERSHIPS: {
> -		int pos, idx, shift;
> +		int pos, idx, shift, err = 0;
>  
> -		err = 0;
>  		netlink_lock_table();
>  		for (pos = 0; pos * 8 < nlk->ngroups; pos += sizeof(u32)) {
>  			if (len - pos < sizeof(u32))
> @@ -1803,40 +1782,32 @@ static int netlink_getsockopt(struct socket *sock, int level, int optname,
>  		if (put_user(ALIGN(nlk->ngroups / 8, sizeof(u32)), optlen))
>  			err = -EFAULT;
>  		netlink_unlock_table();
> -		break;
> +		return err;
>  	}
>  	case NETLINK_CAP_ACK:
> -		if (len < sizeof(int))
> -			return -EINVAL;
> -		len = sizeof(int);
> -		val = nlk->flags & NETLINK_F_CAP_ACK ? 1 : 0;
> -		if (put_user(len, optlen) ||
> -		    put_user(val, optval))
> -			return -EFAULT;
> -		err = 0;
> +		flag = NETLINK_F_CAP_ACK;
>  		break;
>  	case NETLINK_EXT_ACK:
> -		if (len < sizeof(int))
> -			return -EINVAL;
> -		len = sizeof(int);
> -		val = nlk->flags & NETLINK_F_EXT_ACK ? 1 : 0;
> -		if (put_user(len, optlen) || put_user(val, optval))
> -			return -EFAULT;
> -		err = 0;
> +		flag = NETLINK_F_EXT_ACK;
>  		break;
>  	case NETLINK_GET_STRICT_CHK:
> -		if (len < sizeof(int))
> -			return -EINVAL;
> -		len = sizeof(int);
> -		val = nlk->flags & NETLINK_F_STRICT_CHK ? 1 : 0;
> -		if (put_user(len, optlen) || put_user(val, optval))
> -			return -EFAULT;
> -		err = 0;
> +		flag = NETLINK_F_STRICT_CHK;
>  		break;
>  	default:
> -		err = -ENOPROTOOPT;
> +		return -ENOPROTOOPT;
>  	}
> -	return err;
> +
> +	if (len < sizeof(int))

and then check len here.

> +		return -EINVAL;

seems like this chunk (len < sizeof(int)) is not needed.

> +
> +	len = sizeof(int);
> +	val = nlk->flags & flag ? 1 : 0;
> +
> +	if (put_user(len, optlen) ||
> +	    copy_to_user(optval, &val, len))
> +		return -EFAULT;
> +
> +	return 0;
>  }
>  
>  static void netlink_cmsg_recv_pktinfo(struct msghdr *msg, struct sk_buff *skb)

Re: [PATCH v3 net] netlink: Use copy_to_user() for optval in netlink_getsockopt().

[Johannes Berg]

On Sat, 2023-04-22 at 15:57 +0000, David Ahern wrote:
> On 4/21/23 12:52 PM, Kuniyuki Iwashima wrote:
> > diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
> > index f365dfdd672d..9b6eb28e6e94 100644
> > --- a/net/netlink/af_netlink.c
> > +++ b/net/netlink/af_netlink.c
> > @@ -1742,7 +1742,8 @@ static int netlink_getsockopt(struct socket *sock, int level, int optname,
> >  {
> >       struct sock *sk = sock->sk;
> >       struct netlink_sock *nlk = nlk_sk(sk);
> > -     int len, val, err;
> > +     unsigned int flag;
> > +     int len, val;
> 
> len is not initialized here ...
> 
> > 
> >       if (level != SOL_NETLINK)
> >               return -ENOPROTOOPT;
> > @@ -1754,39 +1755,17 @@ static int netlink_getsockopt(struct socket *sock, int level, int optname,
> > 
> >       switch (optname) {

It's initialized in the context here:

        if (get_user(len, optlen))
                return -EFAULT;
        if (len < 0)
                return -EINVAL;

> >       default:
> > -             err = -ENOPROTOOPT;
> > +             return -ENOPROTOOPT;
> >       }
> > -     return err;
> > +
> > +     if (len < sizeof(int))
> 
> and then check len here.

so that's OK. Note how the checks that were there before also were
before the len assignments :)

> > +             return -EINVAL;
> 
> seems like this chunk (len < sizeof(int)) is not needed.

It is, if we get here we need at least the int size for the flags.

johannes

Re: [PATCH v3 net] netlink: Use copy_to_user() for optval in netlink_getsockopt().

[Johannes Berg]

On Fri, 2023-04-21 at 18:52 +0000, Kuniyuki Iwashima wrote:
> Brad Spencer provided a detailed report [0] that when calling getsockopt()
> for AF_NETLINK, some SOL_NETLINK options set only 1 byte even though such
> options require at least sizeof(int) as length.
> 
> The options return a flag value that fits into 1 byte, but such behaviour
> confuses users who do not initialise the variable before calling
> getsockopt() and do not strictly check the returned value as char.
> 
> Currently, netlink_getsockopt() uses put_user() to copy data to optlen and
> optval, but put_user() casts the data based on the pointer, char *optval.
> As a result, only 1 byte is set to optval.
> 
> To avoid this behaviour, we need to use copy_to_user() or cast optval for
> put_user().
> 
> Note that this changes the behaviour on big-endian systems, but we document
> that the size of optval is int in the man page.
> 
>   $ man 7 netlink
>   ...
>   Socket options
>        To set or get a netlink socket option, call getsockopt(2) to read
>        or setsockopt(2) to write the option with the option level argument
>        set to SOL_NETLINK.  Unless otherwise noted, optval is a pointer to
>        an int.
> 
> Fixes: 9a4595bc7e67 ("[NETLINK]: Add set/getsockopt options to support more than 32 groups")
> Fixes: be0c22a46cfb ("netlink: add NETLINK_BROADCAST_ERROR socket option")
> Fixes: 38938bfe3489 ("netlink: add NETLINK_NO_ENOBUFS socket flag")
> Fixes: 0a6a3a23ea6e ("netlink: add NETLINK_CAP_ACK socket option")
> Fixes: 2d4bc93368f5 ("netlink: extended ACK reporting")
> Fixes: 89d35528d17d ("netlink: Add new socket option to enable strict checking on dumps")
> Reported-by: Brad Spencer <bspencer@blackberry.com>
> Link: https://lore.kernel.org/netdev/ZD7VkNWFfp22kTDt@datsun.rim.net/
> Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>


Reviewed-by: Johannes Berg <johannes@sipsolutions.net>

Thanks!

johannes

Re: [PATCH v3 net] netlink: Use copy_to_user() for optval in netlink_getsockopt().

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net.git (main)
by Jakub Kicinski <kuba@kernel.org>:

On Fri, 21 Apr 2023 11:52:55 -0700 you wrote:
> Brad Spencer provided a detailed report [0] that when calling getsockopt()
> for AF_NETLINK, some SOL_NETLINK options set only 1 byte even though such
> options require at least sizeof(int) as length.
> 
> The options return a flag value that fits into 1 byte, but such behaviour
> confuses users who do not initialise the variable before calling
> getsockopt() and do not strictly check the returned value as char.
> 
> [...]

Here is the summary with links:
  - [v3,net] netlink: Use copy_to_user() for optval in netlink_getsockopt().
    https://git.kernel.org/netdev/net/c/d913d32cc270

You are awesome, thank you!
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