Re: [PATCH v2 07/13] ata: libata-core: Remove support for decreasing the number of ports

Hannes Reinecke
2024-06-27T06:35:56Z

On 6/26/24 20:00, Niklas Cassel wrote:
> Commit f31871951b38 ("libata: separate out ata_host_alloc() and
> ata_host_register()") added ata_host_alloc(), where the API allowed
> a LLD to overallocate the number of ports supplied to ata_host_alloc(),
> as long as the LLD decreased host->n_ports before calling
> ata_host_register().
>
> However, this functionally has never ever been used by a single LLD.
>
> Because of the current API design, the assignment of ap->print_id is
> deferred until registration time, which is bad, because that means that
> the ata_port_*() print functions cannot be used by a LLD until after
> registration time, which means that a LLD is forced to use a print
> function that is non-port specific, even for a port specific error.
>
> Remove the support for decreasing the number of ports, such that it will
> be possible to assign ap->print_id earlier.
>
> Signed-off-by: Niklas Cassel <cassel@kernel.org>
> ---
> drivers/ata/libata-core.c | 24 ++++++++++--------------
> include/linux/libata.h | 2 +-
> 2 files changed, 11 insertions(+), 15 deletions(-)
>
> diff --git a/drivers/ata/libata-core.c b/drivers/ata/libata-core.c
> index 591020ea8989..a213a9c0d0a5 100644
> --- a/drivers/ata/libata-core.c
> +++ b/drivers/ata/libata-core.c
> @@ -5550,24 +5550,19 @@ EXPORT_SYMBOL_GPL(ata_host_put);
> /**
> * ata_host_alloc - allocate and init basic ATA host resources
> * @dev: generic device this host is associated with
> - * @max_ports: maximum number of ATA ports associated with this host
> + * @n_ports: the number of ATA ports associated with this host
> *
> * Allocate and initialize basic ATA host resources. LLD calls
> * this function to allocate a host, initializes it fully and
> * attaches it using ata_host_register().
> *
> - * @max_ports ports are allocated and host->n_ports is
> - * initialized to @max_ports. The caller is allowed to decrease
> - * host->n_ports before calling ata_host_register(). The unused
> - * ports will be automatically freed on registration.
> - *
> * RETURNS:
> * Allocate ATA host on success, NULL on failure.
> *
> * LOCKING:
> * Inherited from calling layer (may sleep).
> */
> -struct ata_host *ata_host_alloc(struct device *dev, int max_ports)
> +struct ata_host *ata_host_alloc(struct device *dev, int n_ports)
> {
> struct ata_host *host;
> size_t sz;
> @@ -5575,7 +5570,7 @@ struct ata_host *ata_host_alloc(struct device *dev, int max_ports)
> void *dr;
>
> /* alloc a container for our list of ATA ports (buses) */
> - sz = sizeof(struct ata_host) + (max_ports + 1) * sizeof(void *);
> + sz = sizeof(struct ata_host) + (n_ports + 1) * sizeof(void *);
> host = kzalloc(sz, GFP_KERNEL);
> if (!host)
> return NULL;
> @@ -5595,11 +5590,11 @@ struct ata_host *ata_host_alloc(struct device *dev, int max_ports)
> spin_lock_init(&host->lock);
> mutex_init(&host->eh_mutex);
> host->dev = dev;
> - host->n_ports = max_ports;
> + host->n_ports = n_ports;
> kref_init(&host->kref);
>
> /* allocate ports bound to this host */
> - for (i = 0; i < max_ports; i++) {
> + for (i = 0; i < n_ports; i++) {
> struct ata_port *ap;
>
> ap = ata_port_alloc(host);
> @@ -5908,12 +5903,13 @@ int ata_host_register(struct ata_host *host, const struct scsi_host_template *sh
> return -EINVAL;
> }
>
> - /* Blow away unused ports. This happens when LLD can't
> - * determine the exact number of ports to allocate at
> - * allocation time.
> + /*
> + * For a driver using ata_host_register(), the ports are allocated by
> + * ata_host_alloc(), which also allocates the host->ports array.
> + * The number of array elements must match host->n_ports.
> */
> for (i = host->n_ports; host->ports[i]; i++)
> - kfree(host->ports[i]);
> + WARN_ON(host->ports[i]);
>
What a patently ugly check.
So you are relying on the caller to have zeroed the memory upfront.
But what happens if the caller allocated n_ports, zeroed the memory up
to that point, and then filled in all 'ports' slots?
ports[n_ports - 1] is set to a pointer, but ports[n_ports] is _not_
allocated, and there is no guarantee it'll be zero.
Causing a memory overrun and all sorts of things.

This needs to go, as it's now pointless anyway.

Cheers,

Hannes
--
Dr. Hannes Reinecke Kernel Storage Architect
hare@suse.de +49 911 74053 688
SUSE Software Solutions GmbH, Frankenstr. 146, 90461 Nürnberg
HRB 36809 (AG Nürnberg), GF: I. Totev, A. McDonald, W. Knoblich