Subject: Re: [PATCH] net: 9p: fix possible memory leak in p9_check_errors()

From: [email-masked]
Date: Thu, 26 Oct 2023 20:53:55 +0900

Hangyu Hua wrote on Thu, Oct 26, 2023 at 05:23:51PM +0800:
> When p9pdu_readf is called with "s?d" attribute, it allocates a pointer
> that will store a string. But when p9pdu_readf() fails while handling "d"
> then this pointer will not be freed in p9_check_errors.

Right, that sounds correct to me.

Out of curiosity how did you notice this? The leak shouldn't happen with
any valid server.

This cannot break anything so I'll push this to -next tomorrow and
submit to Linus next week

> Fixes: ca41bb3e21d7 ("[net/9p] Handle Zero Copy TREAD/RERROR case in !dotl case.")

This commit moves this code a bit, but the p9pdu_readf call predates
it -- in this case the Fixes tag is probably not useful; this affects
all maintained kernels.

> Signed-off-by: Hangyu Hua <[email-masked]>
> ---
>  net/9p/client.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/net/9p/client.c b/net/9p/client.c
> index 86bbc7147fc1..6c7cd765b714 100644
> --- a/net/9p/client.c
> +++ b/net/9p/client.c
> @@ -540,12 +540,15 @@ static int p9_check_errors(struct p9_client *c, struct p9_req_t *req)
>  		return 0;
>  
>  	if (!p9_is_proto_dotl(c)) {
> -		char *ename;
> +		char *ename = NULL;
>  
>  		err = p9pdu_readf(&req->rc, c->proto_version, "s?d",
>  				  &ename, &ecode);
> -		if (err)
> +		if (err) {
> +			if (ename != NULL)
> +				kfree(ename);

Don't check for NULL before kfree - kfree does it.
If that's the only remark you get I can fix it when applying the commit
on my side.

>  			goto out_err;
> +		}
>  
>  		if (p9_is_proto_dotu(c) && ecode < 512)
>  			err = -ecode;

-- 
Dominique Martinet | Asmadeus