linux-kernel - Re: [PATCH] net: 9p: fix possible memory leak in p9_check

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Message-ID: <2383398.41Bra3A7bo@silver>
Date:   Thu, 26 Oct 2023 15:18:16 +0200
From:   Christian Schoenebeck <linux_oss@...debyte.com>
To:     Hangyu Hua <hbh25y@...il.com>, asmadeus@...ewreck.org
Cc:     ericvh@...nel.org, lucho@...kov.net, davem@...emloft.net,
        edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com,
        jvrao@...ux.vnet.ibm.com, v9fs@...ts.linux.dev,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net: 9p: fix possible memory leak in p9_check_errors()

On Thursday, October 26, 2023 1:53:55 PM CEST asmadeus@...ewreck.org wrote:
> 
> 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.

Looks like it exists since introduction of p9_check_errors(), therefore:

Fixes: 51a87c552dfd ("9p: rework client code to use new protocol support functions")

> > Signed-off-by: Hangyu Hua <hbh25y@...il.com>
> > ---
> >  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.

With those two remarks addressed:

Reviewed-by: Christian Schoenebeck <linux_oss@...debyte.com>

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