Re: [PATCH net] vxlan: mdb: Fix source list corruption on a failed replace

[Ido Schimmel]

On Tue, Jul 21, 2026 at 12:04:24AM +0800, James Raphael Tiovalen wrote:
> When replacing the source list of an MDB remote entry, all existing
> sources are first marked for deletion and vxlan_mdb_remote_srcs_add()
> is then called to add the new source list. Sources present in the new
> list have their deletion mark cleared, and any sources left marked
> afterwards are removed.
> 
> If vxlan_mdb_remote_srcs_add() fails partway through, its error path
> deletes all entries on the remote's source list. That rollback is only
> correct for its other caller, vxlan_mdb_remote_add(), where the remote
> was just allocated and the list contains solely entries added during
> the call. On the replace path the list also holds pre-existing sources,
> so a failed replace tears them down together with their (S, G)
> forwarding entries instead of leaving the entry unchanged.
> 
> This is reachable from an existing (*, G) remote. An EXCLUDE filter
> that loses sources starts forwarding traffic that should be blocked,
> while an INCLUDE filter that loses sources drops traffic that should be
> forwarded.
> 
> Mark entries created during the current pass with a new
> VXLAN_SGRP_F_NEW flag. On failure, delete only those entries and clear
> the deletion mark on the pre-existing ones, so a failed replace leaves
> the source list untouched. Retain the flag until the whole operation
> succeeds and then clear it. Also stop vxlan_mdb_remote_src_add() from
> deleting a pre-existing entry it only looked up when adding that
> entry's forwarding entry fails.
> 
> Fixes: a3a48de5eade ("vxlan: mdb: Add MDB control path support")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: James Raphael Tiovalen <jamestiotio@xxxxxxxxx>

Reviewed-by: Ido Schimmel <idosch@xxxxxxxxxx>