linux-kernel - [PATCH 3.10 076/139] sctp: fix the check for _sctp_walk_params and _sctp_walk

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Message-Id: <1509571600-4858-27-git-send-email-w@1wt.eu>
Date:   Wed,  1 Nov 2017 22:26:17 +0100
From:   Willy Tarreau <w@....eu>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        linux@...ck-us.net
Cc:     Xin Long <lucien.xin@...il.com>,
        "David S . Miller" <davem@...emloft.net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Willy Tarreau <w@....eu>
Subject: [PATCH 3.10 076/139] sctp: fix the check for _sctp_walk_params and _sctp_walk_errors

From: Xin Long <lucien.xin@...il.com>

commit 6b84202c946cd3da3a8daa92c682510e9ed80321 upstream.

Commit b1f5bfc27a19 ("sctp: don't dereference ptr before leaving
_sctp_walk_{params, errors}()") tried to fix the issue that it
may overstep the chunk end for _sctp_walk_{params, errors} with
'chunk_end > offset(length) + sizeof(length)'.

But it introduced a side effect: When processing INIT, it verifies
the chunks with 'param.v == chunk_end' after iterating all params
by sctp_walk_params(). With the check 'chunk_end > offset(length)
+ sizeof(length)', it would return when the last param is not yet
accessed. Because the last param usually is fwdtsn supported param
whose size is 4 and 'chunk_end == offset(length) + sizeof(length)'

This is a badly issue even causing sctp couldn't process 4-shakes.
Client would always get abort when connecting to server, due to
the failure of INIT chunk verification on server.

The patch is to use 'chunk_end <= offset(length) + sizeof(length)'
instead of 'chunk_end < offset(length) + sizeof(length)' for both
_sctp_walk_params and _sctp_walk_errors.

Fixes: b1f5bfc27a19 ("sctp: don't dereference ptr before leaving _sctp_walk_{params, errors}()")
Signed-off-by: Xin Long <lucien.xin@...il.com>
Acked-by: Neil Horman <nhorman@...driver.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Signed-off-by: Willy Tarreau <w@....eu>
---
 include/net/sctp/sctp.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/include/net/sctp/sctp.h b/include/net/sctp/sctp.h
index b72cba7..ee81c68 100644
--- a/include/net/sctp/sctp.h
+++ b/include/net/sctp/sctp.h
@@ -555,7 +555,7 @@ _sctp_walk_params((pos), (chunk), ntohs((chunk)->chunk_hdr.length), member)
 
 #define _sctp_walk_params(pos, chunk, end, member)\
 for (pos.v = chunk->member;\
-     (pos.v + offsetof(struct sctp_paramhdr, length) + sizeof(pos.p->length) <\
+     (pos.v + offsetof(struct sctp_paramhdr, length) + sizeof(pos.p->length) <=\
       (void *)chunk + end) &&\
      pos.v <= (void *)chunk + end - ntohs(pos.p->length) &&\
      ntohs(pos.p->length) >= sizeof(sctp_paramhdr_t);\
@@ -567,7 +567,7 @@ _sctp_walk_errors((err), (chunk_hdr), ntohs((chunk_hdr)->length))
 #define _sctp_walk_errors(err, chunk_hdr, end)\
 for (err = (sctp_errhdr_t *)((void *)chunk_hdr + \
 	    sizeof(sctp_chunkhdr_t));\
-     ((void *)err + offsetof(sctp_errhdr_t, length) + sizeof(err->length) <\
+     ((void *)err + offsetof(sctp_errhdr_t, length) + sizeof(err->length) <=\
       (void *)chunk_hdr + end) &&\
      (void *)err <= (void *)chunk_hdr + end - ntohs(err->length) &&\
      ntohs(err->length) >= sizeof(sctp_errhdr_t); \
-- 
2.8.0.rc2.1.gbe9624a