Subject: Re: [PATCH] net: 9p: avoid freeing uninit memory in p9pdu_vreadf

From: Dominique Martinet <[email-masked]>
Date: Tue, 5 Dec 2023 18:07:15 +0900

Fedor Pchelkin wrote on Tue, Dec 05, 2023 at 11:05:22AM +0300:
> If an error occurs while processing an array of strings in p9pdu_vreadf
> then uninitialized members of *wnames array are freed.
> 
> Fix this by iterating over only lower indices of the array.
> 
> Found by Linux Verification Center (linuxtesting.org).

You might want to mark that as Reported-by: somehow instead of a free
form comment

> 
> Fixes: ace51c4dd2f9 ("9p: add new protocol support code")
> Signed-off-by: Fedor Pchelkin <[email-masked]>

That aside, it looks good to me -- good find!
I'll push this to Linus with the other pending fix we have next week

> ---
>  net/9p/protocol.c | 7 ++-----
>  1 file changed, 2 insertions(+), 5 deletions(-)
> 
> diff --git a/net/9p/protocol.c b/net/9p/protocol.c
> index 4e3a2a1ffcb3..d33387e74a66 100644
> --- a/net/9p/protocol.c
> +++ b/net/9p/protocol.c
> @@ -393,6 +393,7 @@ p9pdu_vreadf(struct p9_fcall *pdu, int proto_version, const char *fmt,
>  		case 'T':{
>  				uint16_t *nwname = va_arg(ap, uint16_t *);
>  				char ***wnames = va_arg(ap, char ***);
> +				int i;
>  
>  				errcode = p9pdu_readf(pdu, proto_version,
>  								"w", nwname);
> @@ -406,8 +407,6 @@ p9pdu_vreadf(struct p9_fcall *pdu, int proto_version, const char *fmt,
>  				}
>  
>  				if (!errcode) {
> -					int i;
> -
>  					for (i = 0; i < *nwname; i++) {
>  						errcode =
>  						    p9pdu_readf(pdu,
> @@ -421,9 +420,7 @@ p9pdu_vreadf(struct p9_fcall *pdu, int proto_version, const char *fmt,
>  
>  				if (errcode) {
>  					if (*wnames) {
> -						int i;
> -
> -						for (i = 0; i < *nwname; i++)
> +						while (--i >= 0)
>  							kfree((*wnames)[i]);
>  					}
>  					kfree(*wnames);

-- 
Dominique Martinet | Asmadeus