From 38ab1fa981d543e1b00f4ffbce4ddb480cd2effe Mon Sep 17 00:00:00 2001 From: Daniel Borkmann Date: Thu, 28 Aug 2014 15:28:26 +0200 Subject: [PATCH] net: sctp: fix ABI mismatch through sctp_assoc_to_state helper Since SCTP day 1, that is, 19b55a2af145 ("Initial commit") from lksctp tree, the official header carries a copy of enum sctp_sstat_state that looks like (compared to the current in-kernel enumeration): User definition: Kernel definition: enum sctp_sstat_state { typedef enum { SCTP_EMPTY = 0, SCTP_CLOSED = 1, SCTP_STATE_CLOSED = 0, SCTP_COOKIE_WAIT = 2, SCTP_STATE_COOKIE_WAIT = 1, SCTP_COOKIE_ECHOED = 3, SCTP_STATE_COOKIE_ECHOED = 2, SCTP_ESTABLISHED = 4, SCTP_STATE_ESTABLISHED = 3, SCTP_SHUTDOWN_PENDING = 5, SCTP_STATE_SHUTDOWN_PENDING = 4, SCTP_SHUTDOWN_SENT = 6, SCTP_STATE_SHUTDOWN_SENT = 5, SCTP_SHUTDOWN_RECEIVED = 7, SCTP_STATE_SHUTDOWN_RECEIVED = 6, SCTP_SHUTDOWN_ACK_SENT = 8, SCTP_STATE_SHUTDOWN_ACK_SENT = 7, }; } sctp_state_t; This header was later on also placed into the uapi, so that user space programs can compile without having , but the shipped with instead. While RFC6458 under 8.2.1.Association Status (SCTP_STATUS) says that sstat_state can range from SCTP_CLOSED to SCTP_SHUTDOWN_ACK_SENT, we nevertheless have a what it appears to be dummy SCTP_EMPTY state from the very early days. While it seems to do just nothing, commit 0b8f9e25b0aa ("sctp: remove completely unsed EMPTY state") did the right thing and removed this dead code. That however, causes an off-by-one when the user asks the SCTP stack via SCTP_STATUS API and checks for the current socket state thus yielding possibly undefined behaviour in applications as they expect the kernel to tell the right thing. The enumeration had to be changed however as based on the current socket state, we access a function pointer lookup-table through this. Therefore, I think the best way to deal with this is just to add a helper function sctp_assoc_to_state() to encapsulate the off-by-one quirk. Reported-by: Tristan Su Fixes: 0b8f9e25b0aa ("sctp: remove completely unsed EMPTY state") Signed-off-by: Daniel Borkmann Acked-by: Vlad Yasevich Signed-off-by: David S. Miller --- include/net/sctp/sctp.h | 13 +++++++++++++ net/sctp/socket.c | 2 +- 2 files changed, 14 insertions(+), 1 deletion(-) diff --git a/include/net/sctp/sctp.h b/include/net/sctp/sctp.h index f6e7397e799d..9fbd856e6713 100644 --- a/include/net/sctp/sctp.h +++ b/include/net/sctp/sctp.h @@ -320,6 +320,19 @@ static inline sctp_assoc_t sctp_assoc2id(const struct sctp_association *asoc) return asoc ? asoc->assoc_id : 0; } +static inline enum sctp_sstat_state +sctp_assoc_to_state(const struct sctp_association *asoc) +{ + /* SCTP's uapi always had SCTP_EMPTY(=0) as a dummy state, but we + * got rid of it in kernel space. Therefore SCTP_CLOSED et al + * start at =1 in user space, but actually as =0 in kernel space. + * Now that we can not break user space and SCTP_EMPTY is exposed + * there, we need to fix it up with an ugly offset not to break + * applications. :( + */ + return asoc->state + 1; +} + /* Look up the association by its id. */ struct sctp_association *sctp_id2assoc(struct sock *sk, sctp_assoc_t id); diff --git a/net/sctp/socket.c b/net/sctp/socket.c index eb71d49e7653..634a2abb5f3a 100644 --- a/net/sctp/socket.c +++ b/net/sctp/socket.c @@ -4243,7 +4243,7 @@ static int sctp_getsockopt_sctp_status(struct sock *sk, int len, transport = asoc->peer.primary_path; status.sstat_assoc_id = sctp_assoc2id(asoc); - status.sstat_state = asoc->state; + status.sstat_state = sctp_assoc_to_state(asoc); status.sstat_rwnd = asoc->peer.rwnd; status.sstat_unackdata = asoc->unack_data; -- 2.20.1