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

Liam R. Howlett
2019-07-22T12:35:36Z

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@umn.edu> [190720 08:23]:
> From: Wenwen Wang <wenwen@cs.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@cs.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