net/mlx5e: macsec: fix use-after-free of metadata_dst on RX SC delete

Overview

In the Linux kernel, the following vulnerability has been resolved:

net/mlx5e: macsec: fix use-after-free of metadata_dst on RX SC delete

When an offloaded MACsec RX SC is deleted, macsec_del_rxsc_ctx() freed the per-SC metadata_dst with metadata_dst_free(), which kfree()s the object unconditionally and ignores the dst reference count. The RX datapath in mlx5e_macsec_offload_handle_rx_skb() looks up the SC under rcu_read_lock() via xa_load(), takes a reference with dst_hold() and attaches the dst to the skb with skb_dst_set(). A reader that already obtained the rx_sc pointer can race with the delete path and operate on freed memory.

Fix the owner side by dropping the reference with dst_release() instead of freeing unconditionally, and convert the RX datapath to dst_hold_safe() so a reader racing the SC delete cannot attach a dst whose last reference was just dropped; only attach it when a reference was actually taken.

mlx5e_macsec_add_rxsc() also published sc_xarray_element via xa_alloc() before rx_sc->md_dst was allocated and initialised, so a datapath reader that looked the SC up by fs_id could observe rx_sc with md_dst still NULL or, on weakly-ordered architectures, a non-NULL md_dst pointer whose contents were not yet visible. NULL-check the xa_load() result and md_dst on the datapath, and reorder add_rxsc() so the xa_alloc() publish happens only after md_dst is fully initialised; the xarray RCU publish then pairs with the rcu_read_lock()/xa_load() in the datapath.

Note: macsec_del_rxsc_ctx() also kfree()s rx_sc->sc_xarray_element without an RCU grace period while the same datapath reads it under rcu_read_lock(); that is a separate pre-existing issue left to a follow-up patch.

Found by 0sec automated security-research tooling (https://0sec.ai).

Affected

• Linux >= b7c9400cbc48c3713190b3bce4e0c87e924e4104 < b1a4d0c568bbb52c7c04f4fce3c097dae89ed6cb
• Linux >= b7c9400cbc48c3713190b3bce4e0c87e924e4104 < 218cc15a4c907659ad4b0e68c535c61594311205
• Linux >= b7c9400cbc48c3713190b3bce4e0c87e924e4104 < 4a5073b7b30243658f58b2d2d35a823da7fd34d9
• Linux >= b7c9400cbc48c3713190b3bce4e0c87e924e4104 < ed3cc4218070d6b98bf5fb456dccae424fd38c4f
• Linux >= b7c9400cbc48c3713190b3bce4e0c87e924e4104 < 088873af13590ebde10de2ade847f57a05ec61c6
• Linux >= b7c9400cbc48c3713190b3bce4e0c87e924e4104 < de74d8fd10291763d97b218f09adcc7513c975e4
• Linux 6.1

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.