On 08/28/2014 09:28 AM, Daniel Borkmann wrote:
> Since SCTP day 1, that is, 19b55a2af145 ("Initial commit") from lksctp
> tree, the official <netinet/sctp.h> 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, <removed>
> 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 <netinet/sctp.h>, but the shipped
> with <linux/sctp.h> 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 <sooqing@xxxxxxxxx>
> Fixes: 0b8f9e25b0aa ("sctp: remove completely unsed EMPTY state")
> Signed-off-by: Daniel Borkmann <dborkman@xxxxxxxxxx>
Looks good. Thanks.
Acked-by: Vlad Yasevich <vyasevich@xxxxxxxxx>
-vlad
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