The ehash table lookups are lockless and rely on SLAB_TYPESAFE_BY_RCU to guarantee socket memory stability during RCU read-side critical sections. Both tcp_prot and tcpv6_prot have their slab caches created with this flag via proto_register(). However, MPTCP's mptcp_subflow_init() copies tcpv6_prot into tcpv6_prot_override during inet_init() (fs_initcall, level 5), before inet6_init() (module_init/device_initcall, level 6) has called proto_register(&tcpv6_prot). At that point, tcpv6_prot.slab is still NULL, so tcpv6_prot_override.slab remains NULL permanently. This causes MPTCP v6 subflow child sockets to be allocated via kmalloc (falling into kmalloc-4k) instead of the TCPv6 slab cache. The kmalloc-4k cache lacks SLAB_TYPESAFE_BY_RCU, so when these sockets are freed without SOCK_RCU_FREE (which is cleared for child sockets by design), the memory can be immediately reused. Concurrent ehash lookups under rcu_read_lock can then access freed memory, triggering a slab-use-after-free in __inet_lookup_established. Fix this by splitting the IPv6-specific initialization out of mptcp_subflow_init() into a new mptcp_subflow_v6_init(), called from mptcp_proto_v6_init() before protocol registration. This ensures tcpv6_prot_override.slab correctly inherits the SLAB_TYPESAFE_BY_RCU slab cache. Fixes: b19bc2945b40 ("mptcp: implement delegated actions") Cc: stable@vger.kernel.org Signed-off-by: Jiayuan Chen --- net/mptcp/protocol.c | 2 ++ net/mptcp/protocol.h | 1 + net/mptcp/subflow.c | 15 +++++++++------ 3 files changed, 12 insertions(+), 6 deletions(-) diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c index 65c3bb8016f4..614c3f583ca0 100644 --- a/net/mptcp/protocol.c +++ b/net/mptcp/protocol.c @@ -4660,6 +4660,8 @@ int __init mptcp_proto_v6_init(void) { int err; + mptcp_subflow_v6_init(); + mptcp_v6_prot = mptcp_prot; strscpy(mptcp_v6_prot.name, "MPTCPv6", sizeof(mptcp_v6_prot.name)); mptcp_v6_prot.slab = NULL; diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h index 0bd1ee860316..ec15e503da8b 100644 --- a/net/mptcp/protocol.h +++ b/net/mptcp/protocol.h @@ -875,6 +875,7 @@ static inline void mptcp_subflow_tcp_fallback(struct sock *sk, void __init mptcp_proto_init(void); #if IS_ENABLED(CONFIG_MPTCP_IPV6) int __init mptcp_proto_v6_init(void); +void __init mptcp_subflow_v6_init(void); #endif struct sock *mptcp_sk_clone_init(const struct sock *sk, diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c index 6716970693e9..4ff5863aa9fd 100644 --- a/net/mptcp/subflow.c +++ b/net/mptcp/subflow.c @@ -2165,7 +2165,15 @@ void __init mptcp_subflow_init(void) tcp_prot_override.psock_update_sk_prot = NULL; #endif + mptcp_diag_subflow_init(&subflow_ulp_ops); + + if (tcp_register_ulp(&subflow_ulp_ops) != 0) + panic("MPTCP: failed to register subflows to ULP\n"); +} + #if IS_ENABLED(CONFIG_MPTCP_IPV6) +void __init mptcp_subflow_v6_init(void) +{ /* In struct mptcp_subflow_request_sock, we assume the TCP request sock * structures for v4 and v6 have the same size. It should not changed in * the future but better to make sure to be warned if it is no longer @@ -2204,10 +2212,5 @@ void __init mptcp_subflow_init(void) /* Disable sockmap processing for subflows */ tcpv6_prot_override.psock_update_sk_prot = NULL; #endif -#endif - - mptcp_diag_subflow_init(&subflow_ulp_ops); - - if (tcp_register_ulp(&subflow_ulp_ops) != 0) - panic("MPTCP: failed to register subflows to ULP\n"); } +#endif -- 2.43.0