From: Jiayuan Chen Date: Mon, 6 Apr 2026 03:15:10 +0000 (+0800) Subject: mptcp: fix slab-use-after-free in __inet_lookup_established X-Git-Tag: v6.1.169~53 X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=fb1f54b7d16f393b8b65d328410f78b4beea8fcc;p=thirdparty%2Fkernel%2Fstable.git mptcp: fix slab-use-after-free in __inet_lookup_established commit 9b55b253907e7431210483519c5ad711a37dafa1 upstream. 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 Reviewed-by: Matthieu Baerts (NGI0) Link: https://patch.msgid.link/20260406031512.189159-1-jiayuan.chen@linux.dev Signed-off-by: Jakub Kicinski Signed-off-by: Greg Kroah-Hartman --- diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c index 5274b19a5dbd7..965819ddc04c9 100644 --- a/net/mptcp/protocol.c +++ b/net/mptcp/protocol.c @@ -4264,6 +4264,8 @@ int __init mptcp_proto_v6_init(void) { int err; + mptcp_subflow_v6_init(); + mptcp_v6_prot = mptcp_prot; strcpy(mptcp_v6_prot.name, "MPTCPv6"); mptcp_v6_prot.slab = NULL; diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h index 329071f6b9e17..fb3e6ac71bd36 100644 --- a/net/mptcp/protocol.h +++ b/net/mptcp/protocol.h @@ -677,6 +677,7 @@ 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 f9ebcfa1acad6..4377d4058ee61 100644 --- a/net/mptcp/subflow.c +++ b/net/mptcp/subflow.c @@ -1993,7 +1993,15 @@ 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 @@ -2032,10 +2040,5 @@ 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