From: Xin Long lucien.xin@gmail.com
[ Upstream commit 819be8108fded0b9e710bbbf81193e52f7bab2f7 ]
This patch is to fix a NULL-ptr deref in selinux_socket_connect_helper:
[...] kasan: GPF could be caused by NULL-ptr deref or user memory access [...] RIP: 0010:selinux_socket_connect_helper+0x94/0x460 [...] Call Trace: [...] selinux_sctp_bind_connect+0x16a/0x1d0 [...] security_sctp_bind_connect+0x58/0x90 [...] sctp_process_asconf+0xa52/0xfd0 [sctp] [...] sctp_sf_do_asconf+0x785/0x980 [sctp] [...] sctp_do_sm+0x175/0x5a0 [sctp] [...] sctp_assoc_bh_rcv+0x285/0x5b0 [sctp] [...] sctp_backlog_rcv+0x482/0x910 [sctp] [...] __release_sock+0x11e/0x310 [...] release_sock+0x4f/0x180 [...] sctp_accept+0x3f9/0x5a0 [sctp] [...] inet_accept+0xe7/0x720
It was caused by that the 'newsk' sk_socket was not set before going to security sctp hook when processing asconf chunk with SCTP_PARAM_ADD_IP or SCTP_PARAM_SET_PRIMARY:
inet_accept()-> sctp_accept(): lock_sock(): lock listening 'sk' do_softirq(): sctp_rcv(): <-- [1] asconf chunk arrives and enqueued in 'sk' backlog sctp_sock_migrate(): set asoc's sk to 'newsk' release_sock(): sctp_backlog_rcv(): lock 'newsk' sctp_process_asconf() <-- [2] unlock 'newsk' sock_graft(): set sk_socket <-- [3]
As it shows, at [1] the asconf chunk would be put into the listening 'sk' backlog, as accept() was holding its sock lock. Then at [2] asconf would get processed with 'newsk' as asoc's sk had been set to 'newsk'. However, 'newsk' sk_socket is not set until [3], while selinux_sctp_bind_connect() would deref it, then kernel crashed.
Here to fix it by adding the chunk to sk_backlog until newsk sk_socket is set when .accept() is done.
Note that sk->sk_socket can be NULL when the sock is closed, so SOCK_DEAD flag is also needed to check in sctp_newsk_ready().
Thanks to Ondrej for reviewing the code.
Fixes: d452930fd3b9 ("selinux: Add SCTP support") Reported-by: Ying Xu yinxu@redhat.com Suggested-by: Marcelo Ricardo Leitner marcelo.leitner@gmail.com Signed-off-by: Xin Long lucien.xin@gmail.com Acked-by: Marcelo Ricardo Leitner marcelo.leitner@gmail.com Acked-by: Neil Horman nhorman@tuxdriver.com Signed-off-by: Jakub Kicinski jakub.kicinski@netronome.com Signed-off-by: Sasha Levin sashal@kernel.org --- include/net/sctp/sctp.h | 5 +++++ net/sctp/input.c | 12 +++++++++--- 2 files changed, 14 insertions(+), 3 deletions(-)
diff --git a/include/net/sctp/sctp.h b/include/net/sctp/sctp.h index 2abbc15824af..2c6570e6fcfe 100644 --- a/include/net/sctp/sctp.h +++ b/include/net/sctp/sctp.h @@ -625,4 +625,9 @@ static inline __u32 sctp_min_frag_point(struct sctp_sock *sp, __u16 datasize) return sctp_mtu_payload(sp, SCTP_DEFAULT_MINSEGMENT, datasize); }
+static inline bool sctp_newsk_ready(const struct sock *sk) +{ + return sock_flag(sk, SOCK_DEAD) || sk->sk_socket; +} + #endif /* __net_sctp_h__ */ diff --git a/net/sctp/input.c b/net/sctp/input.c index bfe29158afcc..f64d882c8698 100644 --- a/net/sctp/input.c +++ b/net/sctp/input.c @@ -255,7 +255,7 @@ int sctp_rcv(struct sk_buff *skb) bh_lock_sock(sk); }
- if (sock_owned_by_user(sk)) { + if (sock_owned_by_user(sk) || !sctp_newsk_ready(sk)) { if (sctp_add_backlog(sk, skb)) { bh_unlock_sock(sk); sctp_chunk_free(chunk); @@ -333,7 +333,7 @@ int sctp_backlog_rcv(struct sock *sk, struct sk_buff *skb) local_bh_disable(); bh_lock_sock(sk);
- if (sock_owned_by_user(sk)) { + if (sock_owned_by_user(sk) || !sctp_newsk_ready(sk)) { if (sk_add_backlog(sk, skb, sk->sk_rcvbuf)) sctp_chunk_free(chunk); else @@ -348,7 +348,13 @@ int sctp_backlog_rcv(struct sock *sk, struct sk_buff *skb) if (backloged) return 0; } else { - sctp_inq_push(inqueue, chunk); + if (!sctp_newsk_ready(sk)) { + if (!sk_add_backlog(sk, skb, sk->sk_rcvbuf)) + return 0; + sctp_chunk_free(chunk); + } else { + sctp_inq_push(inqueue, chunk); + } }
done: