[PATCH net v2] ice: eswitch: fix use-after-free of metadata_dst in repr release

[Doruk Tan Ozturk]

ice_eswitch_release_repr() frees the port representor metadata_dst via
metadata_dst_free(), which directly kfree()s the object and ignores the
dst_entry refcount. The eswitch slow-path TX routine
ice_eswitch_port_start_xmit() takes a reference on this dst with
dst_hold() and attaches it to the skb via skb_dst_set(). If such an skb
is still in flight (e.g. queued in a qdisc) when the representor is torn
down, the metadata_dst is freed while the skb still points at it. When
the skb is later freed, dst_release() operates on already-freed memory.

Replace metadata_dst_free() with dst_release() so the metadata_dst is
freed only after the last reference is dropped. The dst subsystem frees
metadata_dst objects from dst_destroy() once the refcount reaches zero
(DST_METADATA is set by metadata_dst_alloc()).

Same class of bug and fix as commit c32b26aaa2f9 ("netfilter:
nft_tunnel: fix use-after-free on object destroy").

Fixes: 1a1c40df2e80 ("ice: set and release switchdev environment")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Doruk Tan Ozturk <doruk@xxxxxxx>
Reviewed-by: Simon Horman <horms@xxxxxxxxxx>
---
v2:
 - Correct the Fixes: tag to 1a1c40df2e80 ("ice: set and release
   switchdev environment"); the previously cited fff292b47ac1 only moved
   the affected code rather than introducing the unbalanced free, and the
   bug dates back to when switchdev support was added (Simon Horman).
 - Add Simon Horman's Reviewed-by. No functional change.

 drivers/net/ethernet/intel/ice/ice_eswitch.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/intel/ice/ice_eswitch.c b/drivers/net/ethernet/intel/ice/ice_eswitch.c
index 2e4f0969035f..41b30a7ca4a9 100644
--- a/drivers/net/ethernet/intel/ice/ice_eswitch.c
+++ b/drivers/net/ethernet/intel/ice/ice_eswitch.c
@@ -95,7 +95,7 @@ ice_eswitch_release_repr(struct ice_pf *pf, struct ice_repr *repr)
 		return;

 	ice_vsi_update_security(vsi, ice_vsi_ctx_set_antispoof);
-	metadata_dst_free(repr->dst);
+	dst_release(&repr->dst->dst);
 	repr->dst = NULL;
 	ice_fltr_add_mac_and_broadcast(vsi, repr->parent_mac,
 				       ICE_FWD_TO_VSI);
--
2.43.0