Re: [PATCH v3 09/26] DAX: virtio-fs: Add vhost-user slave commands for mapping

[Stefan Hajnoczi]

On Wed, Apr 28, 2021 at 12:00:43PM +0100, Dr. David Alan Gilbert (git) wrote:
> diff --git a/hw/virtio/vhost-user-fs.c b/hw/virtio/vhost-user-fs.c
> index dd0a02aa99..169a146e72 100644
> --- a/hw/virtio/vhost-user-fs.c
> +++ b/hw/virtio/vhost-user-fs.c
> @@ -45,6 +45,72 @@ static const int user_feature_bits[] = {
>  #define DAX_WINDOW_PROT PROT_NONE
>  #endif
>  
> +/*
> + * The message apparently had 'received_size' bytes, check this
> + * matches the count in the message.
> + *
> + * Returns true if the size matches.
> + */
> +static bool check_slave_message_entries(const VhostUserFSSlaveMsg *sm,
> +                                        int received_size)
> +{
> +    int tmp;
> +
> +    /*
> +     * VhostUserFSSlaveMsg consists of a body followed by 'n' entries,
> +     * (each VhostUserFSSlaveMsgEntry).  There's a maximum of
> +     * VHOST_USER_FS_SLAVE_MAX_ENTRIES of these.
> +     */
> +    if (received_size <= sizeof(VhostUserFSSlaveMsg)) {

received_size is an int and we risk hitting checking against the coerced
size_t value but then using the signed int received_size later. It's
safer to convert to size_t once and then use that size_t value
everywhere later.

> +typedef struct {
> +    /* Offsets within the file being mapped */
> +    uint64_t fd_offset;
> +    /* Offsets within the cache */
> +    uint64_t c_offset;
> +    /* Lengths of sections */
> +    uint64_t len;
> +    /* Flags, from VHOST_USER_FS_FLAG_* */
> +    uint64_t flags;
> +} VhostUserFSSlaveMsgEntry;
> +
> +typedef struct {
> +    /* Number of entries */
> +    uint16_t count;
> +    /* Spare */
> +    uint16_t align;

VhostUserFSSlaveMsgEntry is aligned to 64 bits, so the 16-bit align
field is not sufficient for full alignment.

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