Re: [PATCH kvmtool 3/3] kvmtool: 9p: fix overapping snprintf

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On Thu, Jan 17, 2019 at 01:40:14PM +0100, Anisse Astier wrote:
> GCC 8.2 gives this warning:
> 
> virtio/9p.c: In function ‘virtio_p9_create’:
> virtio/9p.c:335:21: error: passing argument 1 to restrict-qualified parameter aliases with argument 4 [-Werror=restrict]
>   ret = snprintf(dfid->path, size, "%s/%s", dfid->path, name);
>                  ~~~~^~~~~~                 ~~~~~~~~~~
> 
> Fix it by allocating a temporary string with dfid->path content instead
> of overwriting it in-place, which is limited in glibc snprintf with the
> __restrict qualifier.
> 
> Signed-off-by: Anisse Astier <aastier@xxxxxxxxxx>
> ---
>  virtio/9p.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/virtio/9p.c b/virtio/9p.c
> index 69fdc4b..6ae1999 100644
> --- a/virtio/9p.c
> +++ b/virtio/9p.c
> @@ -322,6 +322,7 @@ static void virtio_p9_create(struct p9_dev *p9dev,
>  	struct p9_qid qid;
>  	struct p9_fid *dfid;
>  	char full_path[PATH_MAX];
> +	char *tmp_path;
>  	u32 dfid_val, flags, mode, gid;
>  
>  	virtio_p9_pdu_readf(pdu, "dsddd", &dfid_val,
> @@ -332,7 +333,13 @@ static void virtio_p9_create(struct p9_dev *p9dev,
>  		goto err_out;
>  
>  	size = sizeof(dfid->abs_path) - (dfid->path - dfid->abs_path);
> -	ret = snprintf(dfid->path, size, "%s/%s", dfid->path, name);
> +	tmp_path = strdup(dfid->path);
> +	if (!tmp_path) {
> +		errno = ENOMEM;

Won't errno already be set by the failing strdup?

Will



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