Re: [PATCH v2 1/1] multipathd: verify udev WWIDs with the device before moving paths

[Benjamin Marzinski <bmarzins@redhat.com>]

On Thu, Oct 29, 2026 at 04:52:41PM -0700, Brian Bunker wrote:
> multipathd takes a path's WWID from udev. When a change uevent reports
> a different WWID, uev_update_path() removes the path from its map and
> re-adds it through uev_add_path(), which places it in whatever map owns
> the new WWID. Nothing checks the new value against the device itself;
> recheck_wwid only covers paths coming back up in the checker and
> "multipathd add path". If udev reports the wrong WWID, or the uevent is
> stale by the time it is processed, the path goes into the map of a
> different LUN and I/O for one LUN is silently sent to another.
> 
> Use SG_IO to read VPD page 0x83 from the device in two places, for
> paths where can_recheck_wwid() is true:
> 
> - In uev_update_path(), if the device still reports the cached WWID,
>   ignore the udev value and leave the path where it is.
> 
> - In ev_add_path(), when a path is being re-added because its udev
>   data was missing or changed, refuse to add it if the device doesn't
>   confirm its WWID. The path is orphaned, its WWID is cleared and it
>   is marked INIT_MISSING_UDEV, so the checker retriggers udev (bounded
>   by retrigger_tries) and the path is re-added from fresh data.
> 
> To tell re-adds from ordinary adds, turn the need_do_map argument of
> uev_add_path() and ev_add_path() into enum path_add_mode, with a new
> PATH_ADD_REINIT value that behaves like PATH_ADD_MAP and also requests
> the WWID check. Ordinary adds are unchanged and never read the WWID
> from the device.
> 
> If the SG_IO read fails, behavior is unchanged.
> 
> Split the SG_IO read out of check_path_wwid_change() into
> get_sgio_wwid() so all the checks share it.
> 
> Signed-off-by: Brian Bunker <brian@purestorage.com>
Reviewed-by: Benjamin Marzinski <bmarzins@redhat.com>