linux-kernel - Re: [PATCH] netfilter: ebtables: compat: fix a memory leak bug

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Date:   Mon, 22 Jul 2019 08:32:33 -0400
From:   "Liam R. Howlett" <Liam.Howlett@...cle.com>
To:     Wenwen Wang <wang6495@....edu>
Cc:     Wenwen Wang <wenwen@...uga.edu>,
        Pablo Neira Ayuso <pablo@...filter.org>,
        Jozsef Kadlecsik <kadlec@...filter.org>,
        Florian Westphal <fw@...len.de>,
        Roopa Prabhu <roopa@...ulusnetworks.com>,
        Nikolay Aleksandrov <nikolay@...ulusnetworks.com>,
        "David S. Miller" <davem@...emloft.net>,
        "open list:NETFILTER" <netfilter-devel@...r.kernel.org>,
        "open list:NETFILTER" <coreteam@...filter.org>,
        "moderated list:ETHERNET BRIDGE" <bridge@...ts.linux-foundation.org>,
        "open list:ETHERNET BRIDGE" <netdev@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] netfilter: ebtables: compat: fix a memory leak bug

Nice catch.  The code that exists is confusing due to newinfo->entries
being overwritten and then freed in the existing code path as you state
in your commit log.

* Wenwen Wang <wang6495@....edu> [190720 08:23]:
> From: Wenwen Wang <wenwen@...uga.edu>
> 
> In compat_do_replace(), a temporary buffer is allocated through vmalloc()
> to hold entries copied from the user space. The buffer address is firstly
> saved to 'newinfo->entries', and later on assigned to 'entries_tmp'. Then
> the entries in this temporary buffer is copied to the internal kernel
> structure through compat_copy_entries(). If this copy process fails,
> compat_do_replace() should be terminated. However, the allocated temporary
> buffer is not freed on this path, leading to a memory leak.
> 
> To fix the bug, free the buffer before returning from compat_do_replace().
> 
> Signed-off-by: Wenwen Wang <wenwen@...uga.edu>
> ---
>  net/bridge/netfilter/ebtables.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/net/bridge/netfilter/ebtables.c b/net/bridge/netfilter/ebtables.c
> index 963dfdc..fd84b48e 100644
> --- a/net/bridge/netfilter/ebtables.c
> +++ b/net/bridge/netfilter/ebtables.c
> @@ -2261,8 +2261,10 @@ static int compat_do_replace(struct net *net, void __user *user,
>  	state.buf_kern_len = size64;
>  
>  	ret = compat_copy_entries(entries_tmp, tmp.entries_size, &state);
> -	if (WARN_ON(ret < 0))
> +	if (WARN_ON(ret < 0)) {
> +		vfree(entries_tmp);
>  		goto out_unlock;
> +	}


Would it be worth adding a new goto label above out_unlock and free this
entries_tmp?  It could then be used in previous failure path as well.

Thanks,
Liam