From b0519de8b3f1caf10632aca55def999ec2d2f1bc Mon Sep 17 00:00:00 2001 From: Florian Westphal Date: Thu, 6 Feb 2020 00:39:37 +0100 Subject: [PATCH] mptcp: fix use-after-free for ipv6 Turns out that when we accept a new subflow, the newly created inet_sk(tcp_sk)->pinet6 points at the ipv6_pinfo structure of the listener socket. This wasn't caught by the selftest because it closes the accepted fd before the listening one. adding a close(listenfd) after accept returns is enough: BUG: KASAN: use-after-free in inet6_getname+0x6ba/0x790 Read of size 1 at addr ffff88810e310866 by task mptcp_connect/2518 Call Trace: inet6_getname+0x6ba/0x790 __sys_getpeername+0x10b/0x250 __x64_sys_getpeername+0x6f/0xb0 also alter test program to exercise this. Reported-by: Christoph Paasch Signed-off-by: Florian Westphal Signed-off-by: David S. Miller --- net/mptcp/protocol.c | 36 +++++++++++++++++++++-- tools/testing/selftests/net/mptcp/mptcp_connect.c | 9 ++++++ 2 files changed, 42 insertions(+), 3 deletions(-) diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c index 353f2d1..73780b4 100644 --- a/net/mptcp/protocol.c +++ b/net/mptcp/protocol.c @@ -24,6 +24,13 @@ #define MPTCP_SAME_STATE TCP_MAX_STATES +#if IS_ENABLED(CONFIG_MPTCP_IPV6) +struct mptcp6_sock { + struct mptcp_sock msk; + struct ipv6_pinfo np; +}; +#endif + /* If msk has an initial subflow socket, and the MP_CAPABLE handshake has not * completed yet or has failed, return the subflow socket. * Otherwise return NULL. @@ -627,6 +634,30 @@ static void mptcp_copy_inaddrs(struct sock *msk, const struct sock *ssk) inet_sk(msk)->inet_rcv_saddr = inet_sk(ssk)->inet_rcv_saddr; } +#if IS_ENABLED(CONFIG_MPTCP_IPV6) +static struct ipv6_pinfo *mptcp_inet6_sk(const struct sock *sk) +{ + unsigned int offset = sizeof(struct mptcp6_sock) - sizeof(struct ipv6_pinfo); + + return (struct ipv6_pinfo *)(((u8 *)sk) + offset); +} +#endif + +struct sock *mptcp_sk_clone_lock(const struct sock *sk) +{ + struct sock *nsk = sk_clone_lock(sk, GFP_ATOMIC); + + if (!nsk) + return NULL; + +#if IS_ENABLED(CONFIG_MPTCP_IPV6) + if (nsk->sk_family == AF_INET6) + inet_sk(nsk)->pinet6 = mptcp_inet6_sk(nsk); +#endif + + return nsk; +} + static struct sock *mptcp_accept(struct sock *sk, int flags, int *err, bool kern) { @@ -657,7 +688,7 @@ static struct sock *mptcp_accept(struct sock *sk, int flags, int *err, lock_sock(sk); local_bh_disable(); - new_mptcp_sock = sk_clone_lock(sk, GFP_ATOMIC); + new_mptcp_sock = mptcp_sk_clone_lock(sk); if (!new_mptcp_sock) { *err = -ENOBUFS; local_bh_enable(); @@ -1206,8 +1237,7 @@ int mptcp_proto_v6_init(void) strcpy(mptcp_v6_prot.name, "MPTCPv6"); mptcp_v6_prot.slab = NULL; mptcp_v6_prot.destroy = mptcp_v6_destroy; - mptcp_v6_prot.obj_size = sizeof(struct mptcp_sock) + - sizeof(struct ipv6_pinfo); + mptcp_v6_prot.obj_size = sizeof(struct mptcp6_sock); err = proto_register(&mptcp_v6_prot, 1); if (err) diff --git a/tools/testing/selftests/net/mptcp/mptcp_connect.c b/tools/testing/selftests/net/mptcp/mptcp_connect.c index a3dccd8..99579c0 100644 --- a/tools/testing/selftests/net/mptcp/mptcp_connect.c +++ b/tools/testing/selftests/net/mptcp/mptcp_connect.c @@ -634,6 +634,14 @@ static void check_getpeername_connect(int fd) cfg_host, a, cfg_port, b); } +static void maybe_close(int fd) +{ + unsigned int r = rand(); + + if (r & 1) + close(fd); +} + int main_loop_s(int listensock) { struct sockaddr_storage ss; @@ -657,6 +665,7 @@ int main_loop_s(int listensock) salen = sizeof(ss); remotesock = accept(listensock, (struct sockaddr *)&ss, &salen); if (remotesock >= 0) { + maybe_close(listensock); check_sockaddr(pf, &ss, salen); check_getpeername(remotesock, &ss, salen); -- 2.7.4