linux-kernel - Re: [PATCH net] net: netlink: prevent potential integer overflow in nlmsg

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Message-ID: <62af8b0f-7361-4099-ae20-f5a55e9cffb5@intel.com>
Date: Wed, 22 Jan 2025 14:52:39 +0100
From: Przemek Kitszel <przemyslaw.kitszel@...el.com>
To: Dan Carpenter <dan.carpenter@...aro.org>
CC: "David S. Miller" <davem@...emloft.net>, Thomas Graf <tgraf@...g.ch>,
	"Eric Dumazet" <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo
 Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>,
	<netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<kernel-janitors@...r.kernel.org>
Subject: Re: [PATCH net] net: netlink: prevent potential integer overflow in
 nlmsg_new()

On 1/22/25 14:49, Dan Carpenter wrote:
> The "payload" variable is type size_t, however the nlmsg_total_size()
> function will a few bytes to it and then truncate the result to type
> int.  That means that if "payload" is more than UINT_MAX the alloc_skb()

In the code it's INT_MAX, would be best to have the same used in both
places (or explain it so it's obvious)

> function might allocate a buffer which is smaller than intended.
> 
> Cc: stable@...r.kernel.org
> Fixes: bfa83a9e03cf ("[NETLINK]: Type-safe netlink messages/attributes interface")
> Signed-off-by: Dan Carpenter <dan.carpenter@...aro.org>
> ---
>   include/net/netlink.h | 2 ++
>   1 file changed, 2 insertions(+)
> 
> diff --git a/include/net/netlink.h b/include/net/netlink.h
> index e015ffbed819..ca7a8152e6d4 100644
> --- a/include/net/netlink.h
> +++ b/include/net/netlink.h
> @@ -1015,6 +1015,8 @@ static inline struct nlmsghdr *nlmsg_put_answer(struct sk_buff *skb,
>    */
>   static inline struct sk_buff *nlmsg_new(size_t payload, gfp_t flags)
>   {
> +	if (payload > INT_MAX)
> +		return NULL;
>   	return alloc_skb(nlmsg_total_size(payload), flags);
>   }
>